fix(serve): Support pipeline variable image_uri in ModelBuilder.build

[lucasjia-aws]

Issue

Fixes #5760. Supersedes #5910.

Problem

ModelBuilder.build() fails when image_uri is a pipeline variable such as ParameterString under a PipelineSession, even though ModelBuilder.image_uri is typed Optional[StrPipeVar]. This blocks V2 -> V3 pipeline migrations that parameterize the serving image.

Root cause

The build path treats image_uri as a plain string in two places. First, _build_validations calls is_1p_image_uri(self.image_uri), which slices the value with image_uri[0:12] and raises TypeError: 'ParameterString' object is not subscriptable (the error in the issue). Second, once that is fixed, _create_sagemaker_model evaluates "nova-" in resolved_image_uri for the Nova network-isolation default and raises TypeError: argument of type 'ParameterString' is not iterable. PipelineVariable intentionally defines neither __getitem__ nor __contains__, and its __str__ raises.

#5910 only addresses the first failure, so the reporter's snippet still fails with it applied.

Fix

• is_1p_image_uri returns False for any non-string value. A pipeline variable is only resolved at execution time, so its account cannot be inspected at build time. On the image-only passthrough path both branches of _build_validations lead to passthrough, so the result is unchanged; with a model and no model_server, users now get the existing "Model_server must be set" error instead of a TypeError.
• The Nova network-isolation default in _create_sagemaker_model only inspects string images. For a pipeline-variable image, set enable_network_isolation explicitly if needed.
• The pipeline variable is passed through unchanged, so the pipeline definition renders "Image": {"Get": "Parameters.<name>"}.

Testing

• New tests/unit/test_model_builder_pipeline_variable_image_uri.py: _build_validations passthrough and model_server cases, the _create_sagemaker_model network-isolation check with a pipeline-variable image and a Nova 1P string image (regression guard), and an end-to-end build() under a real PipelineSession asserting the CreateModel request keeps the ParameterString.
• tests/unit/validations/test_check_image_uri.py: ParameterString (with a 1P default value), Join, and None inputs.
• The new tests fail on master and pass with this change. The sagemaker-serve unit test failure set is identical before and after the change.
• Manually verified that a ModelStep built from the result produces a pipeline definition with the parameterized image.

[github-actions]

Claude finished @lucasjia-aws's task in 1m 22s —— View job

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Review

I reviewed the diff against origin/master and traced every caller of the changed function. This is a focused, correct fix. Summary: looks good to merge.

(Note: the inline-comment tool isn't available in this run, so findings are consolidated here with file/line references.)

Correctness ✅

• is_1p_image_uri guard (check_image_uri.py:330-331): Returning False for any non-str is the right call. A PipelineVariable is unresolved at build time, so its account genuinely can't be inspected, and False (not-1P) is the safe classification. I checked all four callers and none regress:
  • model_builder.py:2058 / :2068 — for the image-only case both branches set _passthrough = True regardless, so the result is unchanged (as the PR notes).
  • model_builder.py:2077 — a pipeline-variable image with a model but no model_server now raises the intended "Model_server must be set" ValueError instead of a TypeError. Good.
  • model_builder.py:3701 and model_server/torchserve/prepare.py:56 — the and "xgboost" in image_uri on line 56 is now short-circuited by the leading False, so it never hits the in-on-a-pipeline-var TypeError.
  • utils/telemetry_logger.py:295 — unaffected; also now more robust to None.
• Nova network-isolation guard (model_builder.py:3148): adding isinstance(resolved_image_uri, str) before "nova-" in resolved_image_uri correctly prevents the __contains__ TypeError. The 1P-string regression path is preserved and covered by a test.

Types

• Optional[StrPipeVar] where StrPipeVar = Union[str, PipelineVariable] (pipeline_variable.py:84) is accurate for the callers that pass self.image_uri (typed Optional[StrPipeVar]) and for the None case now handled.

Tests ✅

• Good coverage: _build_validations passthrough + model_server cases, the _create_sagemaker_model isolation check for both a pipeline-var image and a Nova 1P string (regression guard), plus a real-PipelineSession end-to-end build() asserting the ParameterString survives into the CreateModel request. The unit-level check_image_uri tests cover ParameterString (with a 1P default), Join, and None.

Minor observations (non-blocking)

• The new test module uses unittest.TestCase while most of sagemaker-serve/tests/unit uses plain pytest functions. Both run under pytest, so this is purely a style consistency nit.
• test_is_1p_image_uri_pipeline_variable_returns_false deliberately gives the ParameterString a 1P default value to prove the default is not inspected — a nice touch worth keeping.

No security or performance concerns; the change removes failure modes rather than adding surface area, and adheres to the repo's v3-by-default guidance (all examples/tests use sagemaker.serve.ModelBuilder and sagemaker.core.workflow).