Use an environment variable for setting a default docker image

trains/backend_config/entry.py

@@ -101,3 +101,7 @@ class Entry(object):
     def error(self, message):
         # type: (Text) -> None
         pass
+
+    def exists(self):
+        # type: () -> bool
+        return any(key for key in self.keys if self._get(key) is not NotSet)

trains/backend_config/environment.py

@@ -23,3 +23,6 @@ class EnvEntry(Entry):
 
     def error(self, message):
         print("Environment configuration: {}".format(message))
+
+    def exists(self):
+        return any(key for key in self.keys if getenv(key) is not None)

trains/backend_interface/task/task.py

@@ -24,7 +24,7 @@ from ..setupuploadmixin import SetupUploadMixin
 from ..util import make_message, get_or_create_project, get_single_result, \
     exact_match_regex
 from ...config import get_config_for_bucket, get_remote_task_id, TASK_ID_ENV_VAR, get_log_to_backend, \
-    running_remotely, get_cache_dir
+    running_remotely, get_cache_dir, DOCKER_IMAGE_ENV_VAR
 from ...debugging import get_logger
 from ...debugging.log import LoggerRoot
 from ...storage import StorageHelper
@@ -671,6 +671,15 @@ class Task(IdObjectBase, AccessMixin, SetupUploadMixin):
             execution.model_labels = enumeration
             self._edit(execution=execution)
 
+    def _set_default_docker_image(self):
+        if not DOCKER_IMAGE_ENV_VAR.exists():
+            return
+        with self._edit_lock:
+            self.reload()
+            execution = self.data.execution
+            execution.docker_cmd = DOCKER_IMAGE_ENV_VAR.get(default="")
+            self._edit(execution=execution)
+
     def set_artifacts(self, artifacts_list=None):
         """
         List of artifacts (tasks.Artifact) to update the task

trains/config/defs.py

@@ -8,6 +8,7 @@ SESSION_CACHE_FILE = ".session.json"
 DEFAULT_CACHE_DIR = str(Path(tempfile.gettempdir()) / "trains_cache")
 
 TASK_ID_ENV_VAR = EnvEntry("TRAINS_TASK_ID", "ALG_TASK_ID")
+DOCKER_IMAGE_ENV_VAR = EnvEntry("TRAINS_DOCKER_IMAGE", "ALG_DOCKER_IMAGE")
 LOG_TO_BACKEND_ENV_VAR = EnvEntry("TRAINS_LOG_TASK_TO_BACKEND", "ALG_LOG_TASK_TO_BACKEND", type=bool)
 NODE_ID_ENV_VAR = EnvEntry("TRAINS_NODE_ID", "ALG_NODE_ID", type=int)
 PROC_MASTER_ID_ENV_VAR = EnvEntry("TRAINS_PROC_MASTER_ID", "ALG_PROC_MASTER_ID", type=int)