diff --git a/clearml_agent/__main__.py b/clearml_agent/__main__.py
index 93b30c9..0bcc318 100644
--- a/clearml_agent/__main__.py
+++ b/clearml_agent/__main__.py
@@ -12,7 +12,7 @@ from clearml_agent.definitions import FileBuffering, CONFIG_FILE
 from clearml_agent.helper.base import reverse_home_folder_expansion, chain_map, named_temporary_file
 from clearml_agent.helper.process import ExitStatus
 from . import interface, session, definitions, commands
-from .errors import ConfigFileNotFound, Sigterm, APIError
+from .errors import ConfigFileNotFound, Sigterm, APIError, CustomBuildScriptFailed
 from .helper.trace import PackageTrace
 from .interface import get_parser
 
@@ -44,6 +44,8 @@ def run_command(parser, args, command_name):
         debug = command._session.debug_mode
         func = getattr(command, command_name)
         return func(**args_dict)
+    except CustomBuildScriptFailed as e:
+        command_class.exit(e.message, e.errno)
     except ConfigFileNotFound:
         message = 'Cannot find configuration file in "{}".\n' \
                   'To create a configuration file, run:\n' \
diff --git a/clearml_agent/backend_api/config/default/agent.conf b/clearml_agent/backend_api/config/default/agent.conf
index ba6087e..d7a2aa5 100644
--- a/clearml_agent/backend_api/config/default/agent.conf
+++ b/clearml_agent/backend_api/config/default/agent.conf
@@ -35,6 +35,11 @@
     # default false, only the working directory will be added to the PYHTONPATH
     # force_git_root_python_path: false
 
+    # in docker mode, if container's entrypoint automatically activated a virtual environment
+    # use the activated virtual environment and install everything there
+    # set to False to disable, and always create a new venv inheriting from the system_site_packages
+    # docker_use_activated_venv: true
+
     # select python package manager:
     # currently supported: pip, conda and poetry
     # if "pip" or "conda" are used, the agent installs the required packages
@@ -269,4 +274,34 @@
     #       target_format: json
     #     }
     #   }
+
+    # Specifies a custom environment setup script to be executed instead of installing a virtual environment.
+    # If provided, this script is executed following Git cloning. Script command may include environment variable and
+    # will be expanded before execution (e.g. "$CLEARML_GIT_ROOT/script.sh").
+    # The script can also be specified using the CLEARML_AGENT_CUSTOM_BUILD_SCRIPT environment variable.
+    #
+    # When running the script, the following environment variables will be set:
+    # - CLEARML_CUSTOM_BUILD_TASK_CONFIG_JSON: specifies a path to a temporary files containing the complete task
+    #  contents in JSON format
+    # - CLEARML_TASK_SCRIPT_ENTRY: task entrypoint script as defined in the task's script section
+    # - CLEARML_TASK_WORKING_DIR: task working directory as defined in the task's script section
+    # - CLEARML_VENV_PATH: path to the agent's default virtual environment path (as defined in the configuration)
+    # - CLEARML_GIT_ROOT: path to the cloned Git repository
+    # - CLEARML_CUSTOM_BUILD_OUTPUT: a path to a non-existing file that may be created by the script. If created,
+    #  this file must be in the following JSON format:
+    #      ```json
+    #      {
+    #        "binary": "/absolute/path/to/python-executable",
+    #        "entry_point": "/absolute/path/to/task-entrypoint-script",
+    #        "working_dir": "/absolute/path/to/task-working/dir"
+    #      }
+    #      ```
+    #  If provided, the agent will use these instead of the predefined task script section to execute the task and will
+    #  skip virtual environment creation.
+    #
+    # In case the custom script returns with a non-zero exit code, the agent will fail with the same exit code.
+    # In case the custom script is specified but does not exist, or if the custom script does not write valid content
+    # into the file specified in CLEARML_CUSTOM_BUILD_OUTPUT, the agent will emit a warning and continue with the
+    # standard flow.
+    custom_build_script: ""
 }
diff --git a/clearml_agent/backend_api/session/defs.py b/clearml_agent/backend_api/session/defs.py
index 2964bcd..cf266b4 100644
--- a/clearml_agent/backend_api/session/defs.py
+++ b/clearml_agent/backend_api/session/defs.py
@@ -15,6 +15,7 @@ ENV_NO_DEFAULT_SERVER = EnvEntry("CLEARML_NO_DEFAULT_SERVER", "TRAINS_NO_DEFAULT
 ENV_DISABLE_VAULT_SUPPORT = EnvEntry('CLEARML_AGENT_DISABLE_VAULT_SUPPORT', type=bool)
 ENV_ENABLE_ENV_CONFIG_SECTION = EnvEntry('CLEARML_AGENT_ENABLE_ENV_CONFIG_SECTION', type=bool)
 ENV_ENABLE_FILES_CONFIG_SECTION = EnvEntry('CLEARML_AGENT_ENABLE_FILES_CONFIG_SECTION', type=bool)
+ENV_VENV_CONFIGURED = EnvEntry('VIRTUAL_ENV', type=str)
 ENV_INITIAL_CONNECT_RETRY_OVERRIDE = EnvEntry(
     'CLEARML_AGENT_INITIAL_CONNECT_RETRY_OVERRIDE', default=True, converter=safe_text_to_bool
 )
diff --git a/clearml_agent/backend_api/session/session.py b/clearml_agent/backend_api/session/session.py
index e03c683..ace788e 100644
--- a/clearml_agent/backend_api/session/session.py
+++ b/clearml_agent/backend_api/session/session.py
@@ -206,7 +206,7 @@ class Session(TokenManager):
                 http_retries_config = dict(**http_retries_config)
                 http_retries_config['connect'] = connect_retries
 
-        return http_retries_config, get_http_session_with_retry(**http_retries_config)
+        return http_retries_config, get_http_session_with_retry(config=self.config or None, **http_retries_config)
 
     def load_vaults(self):
         if not self.check_min_api_version("2.15") or self.feature_set == "basic":
diff --git a/clearml_agent/commands/worker.py b/clearml_agent/commands/worker.py
index 5855dad..42e53c2 100644
--- a/clearml_agent/commands/worker.py
+++ b/clearml_agent/commands/worker.py
@@ -39,7 +39,9 @@ from clearml_agent.backend_api.services import queues as queues_api
 from clearml_agent.backend_api.services import tasks as tasks_api
 from clearml_agent.backend_api.services import workers as workers_api
 from clearml_agent.backend_api.session import CallResult
-from clearml_agent.backend_api.session.defs import ENV_ENABLE_ENV_CONFIG_SECTION, ENV_ENABLE_FILES_CONFIG_SECTION
+from clearml_agent.backend_api.session.defs import (
+    ENV_ENABLE_ENV_CONFIG_SECTION, ENV_ENABLE_FILES_CONFIG_SECTION,
+    ENV_VENV_CONFIGURED, )
 from clearml_agent.backend_config.defs import UptimeConf
 from clearml_agent.backend_config.utils import apply_environment, apply_files
 from clearml_agent.commands.base import resolve_names, ServiceCommandSection
@@ -65,10 +67,17 @@ from clearml_agent.definitions import (
     ENV_SSH_AUTH_SOCK,
     ENV_AGENT_SKIP_PIP_VENV_INSTALL,
     ENV_EXTRA_DOCKER_ARGS,
+    ENV_CUSTOM_BUILD_SCRIPT, ENV_AGENT_SKIP_PYTHON_ENV_INSTALL, WORKING_STANDALONE_DIR,
 
 )
 from clearml_agent.definitions import WORKING_REPOSITORY_DIR, PIP_EXTRA_INDICES
-from clearml_agent.errors import APIError, CommandFailedError, Sigterm
+from clearml_agent.errors import (
+    APIError,
+    CommandFailedError,
+    Sigterm,
+    SkippedCustomBuildScript,
+    CustomBuildScriptFailed,
+)
 from clearml_agent.helper.base import (
     return_list,
     print_parameters,
@@ -218,7 +227,7 @@ class LiteralScriptManager(object):
             location = None
         location = location or (repo_info and repo_info.root)
         if not location:
-            location = Path(self.venv_folder, "code")
+            location = Path(self.venv_folder, WORKING_STANDALONE_DIR)
             location.mkdir(exist_ok=True, parents=True)
         log.debug("selected execution directory: %s", location)
         return Text(location), self.write(task, location, execution.entry_point)
@@ -698,6 +707,9 @@ class Worker(ServiceCommandSection):
             )
             if self._impersonate_as_task_owner:
                 docker_params["auth_token"] = task_session.token
+            elif self._session.access_key is None or self._session.secret_key is None:
+                # We're using a token right now
+                docker_params["auth_token"] = self._session.token
             if self._worker_tags:
                 docker_params["worker_tags"] = self._worker_tags
             if self._services_mode:
@@ -720,7 +732,7 @@ class Worker(ServiceCommandSection):
                     else:
                         print("Warning: generated docker container name is invalid: {}".format(name))
 
-            full_docker_cmd = self.docker_image_func(**docker_params)
+            full_docker_cmd = self.docker_image_func(env_task_id=task_id, **docker_params)
 
             # if we are using the default docker, update back the Task:
             if default_docker:
@@ -1258,6 +1270,7 @@ class Worker(ServiceCommandSection):
         self._session.print_configuration()
 
     def daemon(self, queues, log_level, foreground=False, docker=False, detached=False, order_fairness=False, **kwargs):
+        self._apply_extra_configuration()
 
         # check that we have docker command if we need it
         if docker not in (False, None) and not check_if_command_exists("docker"):
@@ -1292,8 +1305,12 @@ class Worker(ServiceCommandSection):
 
         # We are not running a daemon we are killing one.
         # find the pid send termination signal and leave
-        if kwargs.get('stop', False):
-            return 1 if not self._kill_daemon(dynamic_gpus=dynamic_gpus) else 0
+        if kwargs.get('stop', False) is not False:
+            return_code = 0
+            for worker_id in kwargs.get('stop') or [None]:
+                if not self._kill_daemon(dynamic_gpus=dynamic_gpus, worker_id=worker_id):
+                    return_code = 1
+            return return_code
 
         # if we do not need to create queues, make sure they are valid
         # match previous behaviour when we validated queue names before everything else
@@ -1772,11 +1789,19 @@ class Worker(ServiceCommandSection):
                              "ERROR! Failed applying git diff, see diff above.".format(diff))
 
     def _apply_extra_configuration(self):
+        # store a few things we updated in runtime (TODO: we should list theme somewhere)
+        agent_config = self._session.config["agent"].copy()
+        agent_config_keys = ["cuda_version", "cudnn_version", "default_python", "worker_id", "debug"]
         try:
             self._session.load_vaults()
         except Exception as ex:
             print("Error: failed applying extra configuration: {}".format(ex))
 
+        # merge back
+        for restore_key in agent_config_keys:
+            if restore_key in agent_config:
+                self._session.config["agent"][restore_key] = agent_config[restore_key]
+
         config = self._session.config
         default = config.get("agent.apply_environment", False)
         if ENV_ENABLE_ENV_CONFIG_SECTION.get(default=default):
@@ -1829,13 +1854,7 @@ class Worker(ServiceCommandSection):
                 requirements = None
 
         if not python_version:
-            try:
-                python_version = current_task.script.binary
-                python_version = python_version.split('/')[-1].replace('python', '')
-                # if we can cast it, we are good
-                python_version = '{:.1f}'.format(float(python_version))
-            except:
-                python_version = None
+            python_version = self._get_task_python_version(current_task)
 
         venv_folder, requirements_manager, is_cached = self.install_virtualenv(
             venv_dir=target, requested_python_version=python_version, execution_info=execution,
@@ -1985,6 +2004,16 @@ class Worker(ServiceCommandSection):
 
         return
 
+    def _get_task_python_version(self, task):
+        # noinspection PyBroadException
+        try:
+            python_ver = task.script.binary
+            python_ver = python_ver.split('/')[-1].replace('python', '')
+            # if we can cast it, we are good
+            return '{:.1f}'.format(float(python_ver))
+        except Exception:
+            pass
+
     @resolve_names
     def execute(
         self,
@@ -2097,85 +2126,140 @@ class Worker(ServiceCommandSection):
 
         execution = self.get_execution_info(current_task)
 
-        if self._session.config.get("agent.package_manager.force_repo_requirements_txt", False):
-            requirements = None
-            print("[package_manager.force_repo_requirements_txt=true] "
-                  "Skipping requirements, using repository \"requirements.txt\" ")
-        else:
+        python_ver = self._get_task_python_version(current_task)
+
+        freeze = None
+        repo_info = None
+        script_dir = ""
+        venv_folder = ""
+
+        custom_build_script = self._session.config.get("agent.custom_build_script", "") or ENV_CUSTOM_BUILD_SCRIPT.get()
+        if custom_build_script:
             try:
-                requirements = current_task.script.requirements
-            except AttributeError:
+                venv_folder = Path(self._session.config["agent.venvs_dir"], python_ver or "3")
+                venv_folder = Path(os.path.expanduser(os.path.expandvars(venv_folder.as_posix())))
+                directory, vcs, repo_info = self.get_repo_info(
+                    execution, current_task, str(venv_folder)
+                )
+                binary, entry_point, working_dir = self.run_custom_build_script(
+                    custom_build_script,
+                    current_task,
+                    execution,
+                    venv_folder=venv_folder,
+                    git_root=vcs.location,
+                )
+
+                execution.entry_point = str(entry_point)
+                execution.working_dir = str(working_dir)
+                script_dir = str(working_dir)
+
+                self.package_api = VirtualenvPip(
+                    session=self._session,
+                    interpreter=str(binary),
+                    python=str(binary),
+                    requirements_manager=RequirementsManager(self._session),
+                    execution_info=execution,
+                    path=venv_folder,
+                )
+
+                self.global_package_api = SystemPip(
+                    session=self._session,
+                    interpreter=str(binary),
+                )
+
+            except SkippedCustomBuildScript as ex:
+                print("Warning: {}".format(str(ex)))
+                custom_build_script = None
+
+        if not custom_build_script:
+            if self._session.config.get("agent.package_manager.force_repo_requirements_txt", False):
                 requirements = None
+                print("[package_manager.force_repo_requirements_txt=true] "
+                      "Skipping requirements, using repository \"requirements.txt\" ")
+            else:
+                try:
+                    requirements = current_task.script.requirements
+                except AttributeError:
+                    requirements = None
 
-        try:
-            python_ver = current_task.script.binary
-            python_ver = python_ver.split('/')[-1].replace('python', '')
-            # if we can cast it, we are good
-            python_ver = '{:.1f}'.format(float(python_ver))
-        except:
-            python_ver = None
+            alternative_code_folder = None
+            if ENV_AGENT_SKIP_PYTHON_ENV_INSTALL.get():
+                venv_folder, requirements_manager, is_cached = None, None, False
+                # we need to create a folder for the code to be dumped into
+                code_folder = self._session.config.get("agent.venvs_dir")
+                code_folder = Path(os.path.expanduser(os.path.expandvars(code_folder)))
+                # let's make sure it is clear from previous runs
+                rm_tree(normalize_path(code_folder, WORKING_REPOSITORY_DIR))
+                rm_tree(normalize_path(code_folder, WORKING_STANDALONE_DIR))
+                if not code_folder.exists():
+                    code_folder.mkdir(parents=True, exist_ok=True)
+                alternative_code_folder = code_folder.as_posix()
+            else:
+                venv_folder, requirements_manager, is_cached = self.install_virtualenv(
+                    standalone_mode=standalone_mode,
+                    requested_python_version=python_ver,
+                    execution_info=execution,
+                    cached_requirements=requirements,
+                )
 
-        venv_folder, requirements_manager, is_cached = self.install_virtualenv(
-            standalone_mode=standalone_mode,
-            requested_python_version=python_ver,
-            execution_info=execution,
-            cached_requirements=requirements,
-        )
+                if not is_cached and not standalone_mode:
+                    if self._default_pip:
+                        self.package_api.install_packages(*self._default_pip)
 
-        if not is_cached and not standalone_mode:
-            if self._default_pip:
-                self.package_api.install_packages(*self._default_pip)
+                    print("\n")
+
+            # either use the venvs base folder for code or the cwd
+            directory, vcs, repo_info = self.get_repo_info(
+                execution, current_task, str(venv_folder or alternative_code_folder)
+            )
 
             print("\n")
 
-        directory, vcs, repo_info = self.get_repo_info(
-            execution, current_task, venv_folder
-        )
+            cwd = vcs.location if vcs and vcs.location else directory
 
-        print("\n")
+            if not standalone_mode:
+                if is_cached:
+                    # reinstalling git / local packages
+                    package_api = copy(self.package_api)
+                    OnlyExternalRequirements.cwd = package_api.cwd = cwd
+                    package_api.requirements_manager = self._get_requirements_manager(
+                        base_interpreter=package_api.requirements_manager.get_interpreter(),
+                        requirement_substitutions=[OnlyExternalRequirements]
+                    )
+                    # make sure we run the handlers
+                    cached_requirements = \
+                        {k: package_api.requirements_manager.replace(requirements[k] or '')
+                         for k in requirements}
+                    if str(cached_requirements.get('pip', '')).strip() \
+                            or str(cached_requirements.get('conda', '')).strip():
+                        package_api.load_requirements(cached_requirements)
+                    # make sure we call the correct freeze
+                    requirements_manager = package_api.requirements_manager
+                elif requirements_manager:
+                    self.install_requirements(
+                        execution,
+                        repo_info,
+                        requirements_manager=requirements_manager,
+                        cached_requirements=requirements,
+                        cwd=cwd,
+                    )
+                elif not self.package_api:
+                    # check if we have to manually configure package API, it will be readonly
+                    self.package_api = SystemPip(session=self._session)
 
-        cwd = vcs.location if vcs and vcs.location else directory
+            # do not update the task packages if we are using conda,
+            # it will most likely make the task environment unreproducible
+            skip_freeze_update = self.is_conda and not self._session.config.get(
+                "agent.package_manager.conda_full_env_update", False)
 
-        if not standalone_mode:
-            if is_cached:
-                # reinstalling git / local packages
-                package_api = copy(self.package_api)
-                OnlyExternalRequirements.cwd = package_api.cwd = cwd
-                package_api.requirements_manager = self._get_requirements_manager(
-                    base_interpreter=package_api.requirements_manager.get_interpreter(),
-                    requirement_substitutions=[OnlyExternalRequirements]
-                )
-                # make sure we run the handlers
-                cached_requirements = \
-                    {k: package_api.requirements_manager.replace(requirements[k] or '')
-                     for k in requirements}
-                if str(cached_requirements.get('pip', '')).strip() \
-                        or str(cached_requirements.get('conda', '')).strip():
-                    package_api.load_requirements(cached_requirements)
-                # make sure we call the correct freeze
-                requirements_manager = package_api.requirements_manager
-            else:
-                self.install_requirements(
-                    execution,
-                    repo_info,
-                    requirements_manager=requirements_manager,
-                    cached_requirements=requirements,
-                    cwd=cwd,
-                )
-
-        # do not update the task packages if we are using conda,
-        # it will most likely make the task environment unreproducible
-        skip_freeze_update = self.is_conda and not self._session.config.get(
-            "agent.package_manager.conda_full_env_update", False)
-
-        freeze = self.freeze_task_environment(
-            task_id=current_task.id,
-            requirements_manager=requirements_manager,
-            add_venv_folder_cache=venv_folder,
-            execution_info=execution,
-            update_requirements=not skip_freeze_update,
-        )
-        script_dir = (directory if isinstance(directory, Path) else Path(directory)).absolute().as_posix()
+            freeze = self.freeze_task_environment(
+                task_id=current_task.id,
+                requirements_manager=requirements_manager,
+                add_venv_folder_cache=venv_folder,
+                execution_info=execution,
+                update_requirements=not skip_freeze_update,
+            )
+            script_dir = (directory if isinstance(directory, Path) else Path(directory)).absolute().as_posix()
 
         # run code
         # print("Running task id [%s]:" % current_task.id)
@@ -2185,7 +2269,9 @@ class Worker(ServiceCommandSection):
             extra.append(
                 WorkerParams(optimization=optimization).get_optimization_flag()
             )
+
         # check if this is a module load, then load it.
+        # noinspection PyBroadException
         try:
             if current_task.script.binary and current_task.script.binary.startswith('python') and \
                     execution.entry_point and execution.entry_point.split()[0].strip() == '-m':
@@ -2193,7 +2279,7 @@ class Worker(ServiceCommandSection):
                 extra.extend(shlex.split(execution.entry_point))
             else:
                 extra.append(execution.entry_point)
-        except:
+        except Exception:
             extra.append(execution.entry_point)
 
         command = self.package_api.get_python_command(extra)
@@ -2577,7 +2663,7 @@ class Worker(ServiceCommandSection):
                     python_version=getattr(self.package_api, 'python', ''),
                     cuda_version=self._session.config.get("agent.cuda_version"),
                     source_folder=add_venv_folder_cache,
-                    exclude_sub_folders=['task_repository', 'code'])
+                    exclude_sub_folders=[WORKING_REPOSITORY_DIR, WORKING_STANDALONE_DIR])
 
         # If do not update back requirements
         if not update_requirements:
@@ -2852,28 +2938,122 @@ class Worker(ServiceCommandSection):
             )
         )
 
-    def install_virtualenv(
-            self,
-            venv_dir=None,
-            requested_python_version=None,
-            standalone_mode=False,
-            execution_info=None,
-            cached_requirements=None,
-    ):
-        # type: (str, str, bool, ExecutionInfo, dict) -> Tuple[Path, RequirementsManager, bool]
+    def run_custom_build_script(self, script, task, execution, venv_folder, git_root):
+        # type: (str, tasks_api.Task, ExecutionInfo, Path, str)-> Tuple[Path, Path, Path]
         """
-        Install a new python virtual environment, removing the old one if exists
-        If CLEARML_SKIP_PIP_VENV_INSTALL is set then an emtpy virtual env folder is created
-        and package manager is configured to work with the global python interpreter (the interpreter
-        path itself can be passed in this variable)
-        :return: virtualenv directory, requirements manager to use with task, True if there is a cached venv entry
+        Run a custom env build script
+        :param script:
+        :return: A tuple containing:
+            - a full path to a python executable
+            - a new task entry_point (replacing the entry_point in the task's script section)
+            - a new working directory (replacing the working_dir in the task's script section)
+            - a requirements manager instance
         """
-        skip_pip_venv_install = ENV_AGENT_SKIP_PIP_VENV_INSTALL.get()
+        script = os.path.expanduser(os.path.expandvars(script))
+
+        try:
+            if not os.path.isfile(script):
+                raise SkippedCustomBuildScript("Build script {} is not found".format(script))
+        except OSError as ex:
+            raise SkippedCustomBuildScript(str(ex))
+
+        print("Running custom build script {}".format(script))
+
+        script_output_file = NamedTemporaryFile(prefix="custom_build_script", suffix=".json", mode="wt", delete=False)
+
+        os.environ["CLEARML_AGENT_CUSTOM_BUILD_SCRIPT"] = script
+        os.environ["CLEARML_CUSTOM_BUILD_TASK_CONFIG_JSON"] = json.dumps(
+            task.to_dict(), separators=(',', ':'), default=str
+        )
+        os.environ["CLEARML_CUSTOM_BUILD_OUTPUT"] = script_output_file.name
+        os.environ["CLEARML_TASK_SCRIPT_ENTRY"] = execution.entry_point
+        os.environ["CLEARML_TASK_WORKING_DIR"] = execution.working_dir
+        os.environ["CLEARML_VENV_PATH"] = str(venv_folder)
+        os.environ["CLEARML_GIT_ROOT"] = git_root
+
+        try:
+            subprocess.check_call([script])
+        except subprocess.CalledProcessError as ex:
+            raise CustomBuildScriptFailed(
+                message="Custom build script failed with return code {}".format(ex.returncode),
+                errno=ex.returncode
+            )
+
+        output = Path(script_output_file.name).read_text()
+        if not output:
+            raise SkippedCustomBuildScript("Build script {} is not found".format(script))
+
+        try:
+            output = json.loads(output)
+            binary = Path(output["binary"])
+            entry_point = Path(output["entry_point"])
+            working_dir = Path(output["working_dir"])
+        except ValueError as ex:
+            raise SkippedCustomBuildScript(
+                "Failed parsing build script output JSON ({}): {}".format(script_output_file.name, ex)
+            )
+        except KeyError as ex:
+            raise SkippedCustomBuildScript("Build script output missing {} field".format(ex.args[0]))
+
+        try:
+            if not binary.is_file():
+                raise SkippedCustomBuildScript(
+                    "Invalid binary path returned from custom build script: {}".format(binary)
+                )
+            if not entry_point.is_file():
+                raise SkippedCustomBuildScript(
+                    "Invalid entrypoint path returned from custom build script: {}".format(entry_point)
+                )
+            if not working_dir.is_dir():
+                raise SkippedCustomBuildScript(
+                    "Invalid working dir returned from custom build script: {}".format(working_dir)
+                )
+        except OSError as ex:
+            raise SkippedCustomBuildScript(str(ex))
+
+        return binary, entry_point, working_dir
+
+    def _get_skip_pip_venv_install(self, skip_pip_venv_install=None):
+        if skip_pip_venv_install is None:
+            skip_pip_venv_install = ENV_AGENT_SKIP_PIP_VENV_INSTALL.get()
+
         if skip_pip_venv_install:
             try:
                 skip_pip_venv_install = bool(strtobool(skip_pip_venv_install))
             except ValueError:
                 pass
+        elif ENV_VENV_CONFIGURED.get() and ENV_DOCKER_IMAGE.get() and \
+                self._session.config.get("agent.docker_use_activated_venv", True) and \
+                self._session.config.get("agent.package_manager.system_site_packages", False):
+            # if we are running inside a container, and virtual environment is already installed,
+            # we should install directly into it, because we cannot inherit from the system packages
+            skip_pip_venv_install = find_executable("python") or True
+
+            # check if we are running inside a container:
+            print(
+                "Warning! Found python virtual environment [{}] already activated inside the container, "
+                "installing packages into venv (pip does not support inherit/nested venv)".format(
+                    skip_pip_venv_install if isinstance(skip_pip_venv_install, str) else ENV_VENV_CONFIGURED.get())
+            )
+        return skip_pip_venv_install
+
+    def install_virtualenv(
+        self,
+        venv_dir=None,
+        requested_python_version=None,
+        standalone_mode=False,
+        execution_info=None,
+        cached_requirements=None,
+    ):
+        # type: (str, str, bool, ExecutionInfo, dict) -> Tuple[Path, RequirementsManager, bool]
+        """
+        Install a new python virtual environment, removing the old one if exists
+        If skip_pip_venv_install is True or contains a string (or if CLEARML_SKIP_PIP_VENV_INSTALL is set)
+        then an emtpy virtual env folder is created and package manager is configured to work with the global python
+        interpreter (or using a custom interpreter if an interpreter path is passed in this variable)
+        :return: virtualenv directory, requirements manager to use with task, True if there is a cached venv entry
+        """
+        skip_pip_venv_install = self._get_skip_pip_venv_install()
 
         if self._session.config.get("agent.ignore_requested_python_version", None):
             requested_python_version = ''
@@ -2930,13 +3110,50 @@ class Worker(ServiceCommandSection):
             or not self.is_venv_update
         )
 
+        if not standalone_mode:
+            rm_tree(normalize_path(venv_dir, WORKING_REPOSITORY_DIR))
+            rm_tree(normalize_path(venv_dir, WORKING_STANDALONE_DIR))
+
+        call_package_manager_create, requirements_manager = self._setup_package_api(
+            executable_name=executable_name,
+            executable_version_suffix=executable_version_suffix,
+            venv_dir=venv_dir,
+            execution_info=execution_info,
+            standalone_mode=standalone_mode,
+            skip_pip_venv_install=skip_pip_venv_install,
+            first_time=first_time,
+        )
+
+        # check if we have a cached folder
+        if cached_requirements and not skip_pip_venv_install and self.package_api.get_cached_venv(
+            requirements=cached_requirements,
+            docker_cmd=execution_info.docker_cmd if execution_info else None,
+            python_version=self.package_api.python,
+            cuda_version=self._session.config.get("agent.cuda_version"),
+            destination_folder=Path(venv_dir)
+        ):
+            print('::: Using Cached environment {} :::'.format(self.package_api.get_last_used_entry_cache()))
+            return venv_dir, requirements_manager, True
+
+        # create the initial venv
+        if not skip_pip_venv_install:
+            if call_package_manager_create:
+                self.package_api.create()
+        else:
+            if not venv_dir.exists():
+                venv_dir.mkdir(parents=True, exist_ok=True)
+
+        return venv_dir, requirements_manager, False
+
+    def _setup_package_api(
+        self, executable_name, executable_version_suffix, venv_dir, execution_info,
+        standalone_mode, skip_pip_venv_install=False, first_time=False
+    ):
+        # type: (str, str, Path, ExecutionInfo, bool, bool, bool) -> Tuple[bool, RequirementsManager]
         requirements_manager = self._get_requirements_manager(
             base_interpreter=executable_name
         )
 
-        if not standalone_mode:
-            rm_tree(normalize_path(venv_dir, WORKING_REPOSITORY_DIR))
-
         package_manager_params = dict(
             session=self._session,
             python=executable_version_suffix if self.is_conda else executable_name,
@@ -2951,7 +3168,6 @@ class Worker(ServiceCommandSection):
         )
 
         call_package_manager_create = False
-
         if not self.is_conda:
             if standalone_mode or skip_pip_venv_install:
                 # pip with standalone mode
@@ -2959,7 +3175,10 @@ class Worker(ServiceCommandSection):
                 if standalone_mode:
                     self.package_api = VirtualenvPip(**package_manager_params)
                 else:
-                    self.package_api = self.global_package_api
+                    # we can change it, no one is going to use it anyhow
+                    package_manager_params['path'] = None
+                    package_manager_params['interpreter'] = executable_name
+                    self.package_api = VirtualenvPip(**package_manager_params)
             else:
                 if self.is_venv_update:
                     self.package_api = VenvUpdateAPI(
@@ -2997,26 +3216,7 @@ class Worker(ServiceCommandSection):
                     venv_dir = new_venv_folder
                     self.package_api = get_conda(path=venv_dir)
 
-        # check if we have a cached folder
-        if cached_requirements and not skip_pip_venv_install and self.package_api.get_cached_venv(
-            requirements=cached_requirements,
-            docker_cmd=execution_info.docker_cmd if execution_info else None,
-            python_version=package_manager_params['python'],
-            cuda_version=self._session.config.get("agent.cuda_version"),
-            destination_folder=Path(venv_dir)
-        ):
-            print('::: Using Cached environment {} :::'.format(self.package_api.get_last_used_entry_cache()))
-            return venv_dir, requirements_manager, True
-
-        # create the initial venv
-        if not skip_pip_venv_install:
-            if call_package_manager_create:
-                self.package_api.create()
-        else:
-            if not venv_dir.exists():
-                venv_dir.mkdir(parents=True, exist_ok=True)
-
-        return venv_dir, requirements_manager, False
+        return call_package_manager_create, requirements_manager
 
     def parse_requirements(self, reqs_file=None, overrides=None):
         os = None
@@ -3266,6 +3466,7 @@ class Worker(ServiceCommandSection):
             worker_tags=None,
             name=None,
             mount_ssh=None, mount_apt_cache=None, mount_pip_cache=None, mount_poetry_cache=None,
+            env_task_id=None,
     ):
         docker = 'docker'
 
@@ -3359,6 +3560,9 @@ class Worker(ServiceCommandSection):
         # update the docker image, so the system knows where it runs
         base_cmd += ['-e', 'CLEARML_DOCKER_IMAGE={} {}'.format(docker_image, ' '.join(docker_arguments or [])).strip()]
 
+        if env_task_id:
+            base_cmd += ['-e', 'CLEARML_TASK_ID={}'.format(env_task_id), ]
+
         if auth_token:
             # if auth token is passed then put it in the env var
             base_cmd += ['-e', '{}={}'.format(ENV_AGENT_AUTH_TOKEN.vars[0], auth_token)]
@@ -3550,8 +3754,11 @@ class Worker(ServiceCommandSection):
 
         return command, script_dir
 
-    def _kill_daemon(self, dynamic_gpus=False):
-        worker_id, worker_name = self._generate_worker_id_name(dynamic_gpus=dynamic_gpus)
+    def _kill_daemon(self, dynamic_gpus=False, worker_id=None):
+        if not worker_id:
+            worker_id, worker_name = self._generate_worker_id_name(dynamic_gpus=dynamic_gpus)
+        else:
+            worker_name = worker_id
 
         # Iterate over all running process
         for pid, uid, slot, file in sorted(Singleton.get_running_pids(), key=lambda x: x[1] or ''):
diff --git a/clearml_agent/definitions.py b/clearml_agent/definitions.py
index b20b357..00a502a 100644
--- a/clearml_agent/definitions.py
+++ b/clearml_agent/definitions.py
@@ -126,6 +126,7 @@ DEFAULT_VENV_UPDATE_URL = (
     "https://raw.githubusercontent.com/Yelp/venv-update/v3.2.4/venv_update.py"
 )
 WORKING_REPOSITORY_DIR = "task_repository"
+WORKING_STANDALONE_DIR = "code"
 DEFAULT_VCS_CACHE = normalize_path(CONFIG_DIR, "vcs-cache")
 PIP_EXTRA_INDICES = [
 ]
@@ -134,6 +135,7 @@ ENV_DOCKER_IMAGE = EnvironmentConfig('CLEARML_DOCKER_IMAGE', 'TRAINS_DOCKER_IMAG
 ENV_WORKER_ID = EnvironmentConfig('CLEARML_WORKER_ID', 'TRAINS_WORKER_ID')
 ENV_WORKER_TAGS = EnvironmentConfig('CLEARML_WORKER_TAGS')
 ENV_AGENT_SKIP_PIP_VENV_INSTALL = EnvironmentConfig('CLEARML_AGENT_SKIP_PIP_VENV_INSTALL')
+ENV_AGENT_SKIP_PYTHON_ENV_INSTALL = EnvironmentConfig('CLEARML_AGENT_SKIP_PYTHON_ENV_INSTALL', type=bool)
 ENV_DOCKER_SKIP_GPUS_FLAG = EnvironmentConfig('CLEARML_DOCKER_SKIP_GPUS_FLAG', 'TRAINS_DOCKER_SKIP_GPUS_FLAG')
 ENV_AGENT_GIT_USER = EnvironmentConfig('CLEARML_AGENT_GIT_USER', 'TRAINS_AGENT_GIT_USER')
 ENV_AGENT_GIT_PASS = EnvironmentConfig('CLEARML_AGENT_GIT_PASS', 'TRAINS_AGENT_GIT_PASS')
@@ -147,6 +149,38 @@ ENV_DOCKER_HOST_MOUNT = EnvironmentConfig('CLEARML_AGENT_K8S_HOST_MOUNT', 'CLEAR
 ENV_VENV_CACHE_PATH = EnvironmentConfig('CLEARML_AGENT_VENV_CACHE_PATH')
 ENV_EXTRA_DOCKER_ARGS = EnvironmentConfig('CLEARML_AGENT_EXTRA_DOCKER_ARGS', type=list)
 
+ENV_CUSTOM_BUILD_SCRIPT = EnvironmentConfig('CLEARML_AGENT_CUSTOM_BUILD_SCRIPT')
+"""
+    Specifies a custom environment setup script to be executed instead of installing a virtual environment.
+    If provided, this script is executed following Git cloning. Script command may include environment variable and
+    will be expanded before execution (e.g. "$CLEARML_GIT_ROOT/script.sh").
+    The script can also be specified using the `agent.custom_build_script` configuration setting.
+    
+    When running the script, the following environment variables will be set:
+    - CLEARML_CUSTOM_BUILD_TASK_CONFIG_JSON: specifies a path to a temporary files containing the complete task
+     contents in JSON format
+    - CLEARML_TASK_SCRIPT_ENTRY: task entrypoint script as defined in the task's script section
+    - CLEARML_TASK_WORKING_DIR: task working directory as defined in the task's script section
+    - CLEARML_VENV_PATH: path to the agent's default virtual environment path (as defined in the configuration)
+    - CLEARML_GIT_ROOT: path to the cloned Git repository
+    - CLEARML_CUSTOM_BUILD_OUTPUT: a path to a non-existing file that may be created by the script. If created,
+     this file must be in the following JSON format:
+         ```json
+         {
+           "binary": "/absolute/path/to/python-executable",
+           "entry_point": "/absolute/path/to/task-entrypoint-script",
+           "working_dir": "/absolute/path/to/task-working/dir"
+         }
+         ```
+     If provided, the agent will use these instead of the predefined task script section to execute the task and will
+     skip virtual environment creation.
+    
+    In case the custom script returns with a non-zero exit code, the agent will fail with the same exit code.
+    In case the custom script is specified but does not exist, or if the custom script does not write valid content
+    into the file specified in CLEARML_CUSTOM_BUILD_OUTPUT, the agent will emit a warning and continue with the
+    standard flow.
+"""
+
 
 class FileBuffering(IntEnum):
     """
diff --git a/clearml_agent/errors.py b/clearml_agent/errors.py
index b4d6bc8..00f7694 100644
--- a/clearml_agent/errors.py
+++ b/clearml_agent/errors.py
@@ -84,3 +84,13 @@ class MissingPackageError(CommandFailedError):
     def __str__(self):
         return '{self.__class__.__name__}: ' \
                '"{self.name}" package is required. Please run "pip install {self.name}"'.format(self=self)
+
+
+class CustomBuildScriptFailed(CommandFailedError):
+    def __init__(self, errno, *args, **kwargs):
+        super(CustomBuildScriptFailed, self).__init__(*args, **kwargs)
+        self.errno = errno
+
+
+class SkippedCustomBuildScript(CommandFailedError):
+    pass
diff --git a/clearml_agent/helper/base.py b/clearml_agent/helper/base.py
index aa881a1..8a07832 100644
--- a/clearml_agent/helper/base.py
+++ b/clearml_agent/helper/base.py
@@ -506,6 +506,38 @@ def is_conda(config):
     return config['agent.package_manager.type'].lower() == 'conda'
 
 
+def convert_cuda_version_to_float_single_digit_str(cuda_version):
+    """
+    Convert a cuda_version (string/float/int) into a float representation, e.g. 11.4
+    Notice returns String Single digit only!
+    :return str:
+    """
+    cuda_version = str(cuda_version or 0)
+    # if we have patch version we parse it here
+    cuda_version_parts = [int(v) for v in cuda_version.split('.')]
+    if len(cuda_version_parts) > 1 or cuda_version_parts[0] < 60:
+        cuda_version = 10 * cuda_version_parts[0]
+        if len(cuda_version_parts) > 1:
+            cuda_version += float(".{:d}".format(cuda_version_parts[1]))*10
+
+        cuda_version_full = "{:.1f}".format(float(cuda_version) / 10.)
+    else:
+        cuda_version = cuda_version_parts[0]
+        cuda_version_full = "{:.1f}".format(float(cuda_version) / 10.)
+
+    return cuda_version_full
+
+
+def convert_cuda_version_to_int_10_base_str(cuda_version):
+    """
+    Convert a cuda_version (string/float/int) into an integer version, e.g. 112 for cuda 11.2
+    Return string
+    :return str:
+    """
+    cuda_version = convert_cuda_version_to_float_single_digit_str(cuda_version)
+    return str(int(float(cuda_version)*10))
+
+
 class NonStrictAttrs(object):
 
     @classmethod
diff --git a/clearml_agent/helper/package/conda_api.py b/clearml_agent/helper/package/conda_api.py
index 0ffd506..2d94f5f 100644
--- a/clearml_agent/helper/package/conda_api.py
+++ b/clearml_agent/helper/package/conda_api.py
@@ -19,7 +19,9 @@ from clearml_agent.external.requirements_parser import parse
 from clearml_agent.external.requirements_parser.requirement import Requirement
 
 from clearml_agent.errors import CommandFailedError
-from clearml_agent.helper.base import rm_tree, NonStrictAttrs, select_for_platform, is_windows_platform, ExecutionInfo
+from clearml_agent.helper.base import (
+    rm_tree, NonStrictAttrs, select_for_platform, is_windows_platform, ExecutionInfo,
+    convert_cuda_version_to_float_single_digit_str, convert_cuda_version_to_int_10_base_str, )
 from clearml_agent.helper.process import Argv, Executable, DEVNULL, CommandSequence, PathLike
 from clearml_agent.helper.package.requirements import SimpleVersion
 from clearml_agent.session import Session
@@ -167,7 +169,7 @@ class CondaAPI(PackageManager):
                 raise ValueError("Could not restore Conda environment, cannot find {}".format(
                     self.conda_pre_build_env_path))
 
-        output = Argv(
+        command = Argv(
             self.conda,
             "create",
             "--yes",
@@ -175,7 +177,9 @@ class CondaAPI(PackageManager):
             "--prefix",
             self.path,
             "python={}".format(self.python),
-        ).get_output(stderr=DEVNULL)
+        )
+        print('Executing Conda: {}'.format(command.serialize()))
+        output = command.get_output(stderr=DEVNULL)
         match = re.search(
             r"\W*(.*activate) ({})".format(re.escape(str(self.path))), output
         )
@@ -457,16 +461,8 @@ class CondaAPI(PackageManager):
             if not cuda_version:
                 cuda_version = 0
             else:
-                cuda_version_full = str(cuda_version)
-                # if we have patch version we parse it here
-                cuda_version_parts = [int(v) for v in cuda_version.split('.')]
-                if len(cuda_version_parts) > 1 or cuda_version_parts[0] < 60:
-                    cuda_version = 10*cuda_version_parts[0]
-                    if len(cuda_version_parts) > 1:
-                        cuda_version += cuda_version_parts[1]
-                else:
-                    cuda_version = cuda_version_parts[0]
-                    cuda_version_full = "{:.1f}".format(float(cuda_version)/10.)
+                cuda_version_full = convert_cuda_version_to_float_single_digit_str(cuda_version)
+                cuda_version = int(convert_cuda_version_to_int_10_base_str(cuda_version))
         except Exception:
             cuda_version = 0
 
diff --git a/clearml_agent/helper/package/pip_api/venv.py b/clearml_agent/helper/package/pip_api/venv.py
index 868d7f6..3a41287 100644
--- a/clearml_agent/helper/package/pip_api/venv.py
+++ b/clearml_agent/helper/package/pip_api/venv.py
@@ -12,7 +12,7 @@ from ..requirements import RequirementsManager
 
 class VirtualenvPip(SystemPip, PackageManager):
     def __init__(self, session, python, requirements_manager, path, interpreter=None, execution_info=None, **kwargs):
-        # type: (Session, float, RequirementsManager, PathLike, PathLike, ExecutionInfo, Any) -> ()
+        # type: (Session, str, RequirementsManager, PathLike, PathLike, ExecutionInfo, Any) -> ()
         """
         Program interface to virtualenv pip.
         Must be given either path to virtualenv or source command.
@@ -48,7 +48,7 @@ class VirtualenvPip(SystemPip, PackageManager):
         return Argv.conditional_flag(
             self.session.config["agent.package_manager.system_site_packages"],
             "--system-site-packages",
-        ) + ("--python", self._bin)
+        )
 
     def install_flags(self):
         """
@@ -64,10 +64,6 @@ class VirtualenvPip(SystemPip, PackageManager):
         Only valid if instantiated with path.
         Use self.python as self.bin does not exist.
         """
-        # Log virtualenv information to stdout
-        self.session.command(
-            self.python, "-m", "virtualenv", "--version"
-        )
         self.session.command(
             self.python, "-m", "virtualenv", self.path, *self.create_flags()
         ).check_call()
diff --git a/clearml_agent/helper/package/pytorch.py b/clearml_agent/helper/package/pytorch.py
index 6b8b03a..5b2ef15 100644
--- a/clearml_agent/helper/package/pytorch.py
+++ b/clearml_agent/helper/package/pytorch.py
@@ -174,36 +174,42 @@ class PytorchRequirement(SimpleSubstitution):
         self.log = self._session.get_logger(__name__)
         self.package_manager = self.config["agent.package_manager.type"].lower()
         self.os = os_name or self.get_platform()
-        self.cuda = "cuda{}".format(self.cuda_version).lower()
-        self.python_version_string = str(self.config["agent.default_python"])
-        self.python_major_minor_str = '.'.join(self.python_version_string.split('.')[:2])
-        if '.' not in self.python_major_minor_str:
-            raise PytorchResolutionError(
-                "invalid python version {!r} defined in configuration file, key 'agent.default_python': "
-                "must have both major and minor parts of the version (for example: '3.7')".format(
-                    self.python_version_string
-                )
-            )
-        self.python = "python{}".format(self.python_major_minor_str)
-
-        self.exceptions = [
-            PytorchResolutionError(message)
-            for message in (
-                None,
-                'cuda version "{}" is not supported'.format(self.cuda),
-                'python version "{}" is not supported'.format(
-                    self.python_version_string
-                ),
-            )
-        ]
-
-        try:
-            self.validate_python_version()
-        except PytorchResolutionError as e:
-            self.log.warn("will not be able to install pytorch wheels: %s", e.args[0])
-
+        self.cuda = None
+        self.python_version_string = None
+        self.python_major_minor_str = None
+        self.python = None
+        self.exceptions = []
         self._original_req = []
 
+    def _init_python_ver_cuda_ver(self):
+        if self.cuda is None:
+            self.cuda = "cuda{}".format(self.cuda_version).lower()
+        if self.python_version_string is None:
+            self.python_version_string = str(self.config["agent.default_python"])
+        if self.python_major_minor_str is None:
+            self.python_major_minor_str = '.'.join(self.python_version_string.split('.')[:2])
+            if '.' not in self.python_major_minor_str:
+                raise PytorchResolutionError(
+                    "invalid python version {!r} defined in configuration file, key 'agent.default_python': "
+                    "must have both major and minor parts of the version (for example: '3.7')".format(
+                        self.python_version_string
+                    )
+                )
+        if self.python is None:
+            self.python = "python{}".format(self.python_major_minor_str)
+
+        if not self.exceptions:
+            self.exceptions = [
+                PytorchResolutionError(message)
+                for message in (
+                    None,
+                    'cuda version "{}" is not supported'.format(self.cuda),
+                    'python version "{}" is not supported'.format(
+                        self.python_version_string
+                    ),
+                )
+            ]
+
     @property
     def is_conda(self):
         return self.package_manager == "conda"
@@ -216,6 +222,8 @@ class PytorchRequirement(SimpleSubstitution):
         """
         Make sure python version has both major and minor versions as required for choosing pytorch wheel
         """
+        self._init_python_ver_cuda_ver()
+
         if self.is_pip and not self.python_major_minor_str:
             raise PytorchResolutionError(
                 "invalid python version {!r} defined in configuration file, key 'agent.default_python': "
@@ -294,6 +302,7 @@ class PytorchRequirement(SimpleSubstitution):
 
     def get_url_for_platform(self, req):
         # check if package is already installed with system packages
+        self.validate_python_version()
         # noinspection PyBroadException
         try:
             if self.config.get("agent.package_manager.system_site_packages", None):
diff --git a/clearml_agent/helper/package/requirements.py b/clearml_agent/helper/package/requirements.py
index 501c893..b19f8a8 100644
--- a/clearml_agent/helper/package/requirements.py
+++ b/clearml_agent/helper/package/requirements.py
@@ -16,7 +16,9 @@ from pyhocon import ConfigTree
 import six
 import logging
 from clearml_agent.definitions import PIP_EXTRA_INDICES
-from clearml_agent.helper.base import warning, is_conda, which, join_lines, is_windows_platform
+from clearml_agent.helper.base import (
+    warning, is_conda, which, join_lines, is_windows_platform,
+    convert_cuda_version_to_int_10_base_str, )
 from clearml_agent.helper.process import Argv, PathLike
 from clearml_agent.helper.gpu.gpustat import get_driver_cuda_version
 from clearml_agent.session import Session, normalize_cuda_version
@@ -474,7 +476,7 @@ class RequirementSubstitution(object):
 
     @property
     def cuda_version(self):
-        return self.config['agent.cuda_version']
+        return convert_cuda_version_to_int_10_base_str(self.config['agent.cuda_version'])
 
     @property
     def cudnn_version(self):
diff --git a/clearml_agent/interface/worker.py b/clearml_agent/interface/worker.py
index bc4b23c..47ee0c2 100644
--- a/clearml_agent/interface/worker.py
+++ b/clearml_agent/interface/worker.py
@@ -99,8 +99,10 @@ DAEMON_ARGS = dict({
         'aliases': ['-d'],
     },
     '--stop': {
-        'help': 'Stop the running agent (based on the same set of arguments)',
-        'action': 'store_true',
+        'help': 'Stop the running agent (based on the same set of arguments). '
+                'Optional: provide a list of specific local worker IDs to stop',
+        'nargs': '*',
+        'default': False,
     },
     '--dynamic-gpus': {
         'help': 'Allow to dynamically allocate gpus based on queue properties, '