Merge pull request #121 from lsst-sqre/tickets/DM-33742

DM-33742: Introduce cachemachine_image_policy to mobu

src/mobu/cachemachine.py

@@ -3,7 +3,6 @@
 from __future__ import annotations
 
 from typing import TYPE_CHECKING
-from urllib.parse import urljoin
 
 from .config import config
 from .exceptions import CachemachineError
@@ -30,8 +29,11 @@ def __init__(
         self._session = session
         self._token = token
         self._username = username
-        self._url = urljoin(
-            config.environment_url, "cachemachine/jupyter/available"
+        # Should be configurable between available and desired
+        self._url = (
+            config.environment_url
+            + "/cachemachine/jupyter/"
+            + config.cachemachine_image_policy
         )
 
     async def get_latest_weekly(self) -> JupyterImage:

src/mobu/config.py

@@ -37,6 +37,17 @@ class Configuration:
     Set with the ``ENVIRONMENT_URL`` environment variable.
     """
 
+    cachemachine_image_policy: str = os.getenv(
+        "CACHEMACHINE_IMAGE_POLICY", "available"
+    )
+    """Whether to use the images available on all nodes, or the images
+    desired by cachemachine.  In instances where image streaming is enabled,
+    and therefore pulls are fast, ``desired`` is preferred.  The default is
+    ``available``.
+
+    Set with the ``CACHEMACHINE_IMAGE_POLICY`` environment variable.
+    """
+
     gafaelfawr_token: Optional[str] = os.getenv("GAFAELFAWR_TOKEN")
     """The Gafaelfawr admin token to use to create user tokens.