Do not request image config for default images

src/dstack/_internal/server/services/jobs/configurators/base.py

@@ -280,7 +280,7 @@ def _image_name(self) -> str:
 
     async def _user(self) -> Optional[UnixUser]:
         user = self.run_spec.configuration.user
-        if user is None:
+        if user is None and self.run_spec.configuration.image is not None:
             image_config = await self._get_image_config()
             user = image_config.user
         if user is None:

src/tests/_internal/server/services/jobs/test_jobs.py

@@ -0,0 +1,69 @@
+from unittest.mock import patch
+
+import pytest
+
+from dstack._internal.core.models.configurations import TaskConfiguration
+from dstack._internal.core.models.profiles import Profile
+from dstack._internal.core.models.repos.local import LocalRunRepoData
+from dstack._internal.core.models.runs import RunSpec
+from dstack._internal.server.services.docker import ImageConfig
+from dstack._internal.server.services.jobs import get_job_specs_from_run_spec
+
+
+@pytest.mark.parametrize(
+    "configuration, expected_calls",
+    [
+        pytest.param(
+            # No need to request the registry if our default image is used.
+            TaskConfiguration(commands=["sleep infinity"]),
+            0,
+            id="default-dstack-image",
+        ),
+        pytest.param(
+            TaskConfiguration(image="ubuntu"),
+            1,
+            id="custom-image",
+        ),
+        pytest.param(
+            TaskConfiguration(image="ubuntu", commands=["sleep infinity"]),
+            1,
+            id="custom-image-with-commands",
+        ),
+        pytest.param(
+            TaskConfiguration(image="ubuntu", user="root"),
+            1,
+            id="custom-image-with-user",
+        ),
+        pytest.param(
+            # Setting `commands` and `user` is a known hack that we advertised to some customers
+            # to avoid registry requests.
+            TaskConfiguration(image="ubuntu", commands=["sleep infinity"], user="root"),
+            0,
+            id="custom-image-with-commands-and-user",
+        ),
+    ],
+)
+@pytest.mark.asyncio
+async def test_get_job_specs_from_run_spec_image_config_calls(
+    configuration: TaskConfiguration, expected_calls: int
+) -> None:
+    """
+    Test the number of times we attempt to fetch the image config from the Docker registry.
+
+    Whenever possible, we prefer not to request the registry to avoid hitting rate limits.
+    """
+
+    run_spec = RunSpec(
+        run_name="test-run",
+        repo_data=LocalRunRepoData(repo_dir="/"),
+        configuration=configuration,
+        profile=Profile(name="default"),
+        ssh_key_pub="user_ssh_key",
+    )
+    fake_image_config = ImageConfig.parse_obj({"Entrypoint": ["/bin/bash"]})
+    with patch(
+        "dstack._internal.server.services.jobs.configurators.base._get_image_config",
+        return_value=fake_image_config,
+    ) as mock_get_image_config:
+        await get_job_specs_from_run_spec(run_spec=run_spec, secrets={}, replica_num=0)
+        assert mock_get_image_config.call_count == expected_calls