Return the last 5xx response when retries run out

[codechrl]

The default PoolManager built in Minio.__init__() retries 500, 502, 503 and 504, and leaves urllib3's raise_on_status at its default of True:

retries=Retry(
    total=5,
    backoff_factor=0.2,
    status_forcelist=[500, 502, 503, 504]
)

When the server still answers 5xx after the last retry, urlopen() raises instead of returning the response. _url_open() never sees it, so the code that turns an error body into an S3Error does not run for these statuses. A server that keeps answering 503 SlowDown gives the caller:

urllib3.exceptions.MaxRetryError: HTTPConnectionPool(host='localhost', port=45701): Max retries exceeded with url: /hello?policy= (Caused by ResponseError('too many 503 error responses'))

The error code and request ID are lost. except S3Error does not catch it.

raise_on_status=False makes urllib3 return the last response once retries are exhausted. The number of attempts is unchanged. When that response carries an XML error body, _url_open() raises S3Error with its code and request ID, as it does for 4xx. MinioAdmin and IamAwsProvider build the same Retry and get the same change, so they now raise MinioAdminException and ValueError with the status code. The other credential providers only send POST. The default Retry.allowed_methods excludes POST, so those providers already see the response and are left alone. The custom-client example in the docstring and in docs/API.md is updated to match.

Tested against a local HTTP server that answers every request with 503 and a SlowDown XML body. Six requests are sent before and after the change. Before, get_bucket_policy() raises MaxRetryError. After, it raises S3Error with code='SlowDown'. MinioAdmin.info() and IamAwsProvider.retrieve() were checked the same way. No unit test is added. The retry loop runs in urllib3, below MockConnection. A test would need a real HTTP server. Nothing in tests/unit starts one. Not run against a live MinIO or S3 server.

Summary by CodeRabbit

• Bug Fixes
  • HTTP clients now handle retryable server responses without prematurely raising errors, allowing existing status handling to run as expected. Retry status codes and limits remain unchanged.

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📝 Walkthrough

Walkthrough

Retry configurations in the MinIO clients, IAM provider, and proxy examples now set raise_on_status=False. The configured retry status codes remain unchanged.

Changes

Retry Status Handling

Layer / File(s)	Summary
Set retry status handling docs/API.md, minio/minio.py, minio/credentials/providers.py, minio/minioadmin.py	Retry configurations in the clients and IAM provider set raise_on_status=False. Proxy examples use the same setting. Existing retry status codes remain unchanged.

Priority: ➖ Normal

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Bug fix

Suggested reviewers: balamurugana

Merge Risk: 🟡 Moderate · up to d4d8f

Installations using urllib3 before 1.15 will fail when constructing Minio, MinioAdmin, or IamAwsProvider. Declare the minimum supported urllib3 version before merging.

Security Architecture Review

Security architecture risk: 🟡 Moderate · up to d4d8f

Returning the final server response improves error reporting, but a prolonged credential-service outage can now trigger a different credential source. Environments pinned to older HTTP library versions may also fail to construct clients.

Retained concerns

• Medium · security · inferred: An exhausted IAM metadata 5xx now raises ValueError, allowing a configured credential chain to select another authority where the previous retry exception stopped retrieval. A selected non-expiring static fallback can remain in use after IAM recovers.
• Low · reliability · inferred: The new Retry keyword can prevent default client and IAM provider construction on an installed urllib3 version predating support for raise_on_status, although the package declares no minimum version.

Security review details

Security Blast Radius

• inferred — The credential-authority effect is limited to callers that place IamAwsProvider in a chain with a usable fallback and encounter exhausted retryable metadata responses. No production provider ordering or broader tenant exposure was established.

Security Findings and Attack Paths

• inferred — A party able to keep the configured IAM metadata endpoint returning retryable 5xx responses could cause a configured chain to advance to another credential provider. Any resulting authority depends on that caller's fallback ordering and credentials, not on accepting the 5xx response body.

Trust Boundaries and Controls

• observed — The response-status check remains before credential parsing, and cached credentials return only while locally considered unexpired. Neither control establishes that a caller-configured fallback has equivalent privileges to the IAM identity.

Resilience and Maintainability Implications

• inferred — Because static fallback credentials have no expiration and chain selection is cached, recovery of the metadata endpoint alone need not restore the intended IAM identity.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: returning the final 5xx response when retries are exhausted.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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Inline comments:
In @minio/minio.py:
- Around line 229-230: Update the urllib3 dependency declaration to require
version 1.15 or newer so the Retry constructor accepts raise_on_status when
constructing Minio, MinioAdmin, or IamAwsProvider.

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