[Serve] Fix enable_access_log=False not suppressing access logs on stderr

[kouroshHakha]

Summary

LoggingConfig(enable_access_log=False) does not suppress access logs from stderr. The log_access_log_filter is only applied to the file handler (memory_handler), not the stream_handler. Since RAY_SERVE_LOG_TO_STDERR defaults to True, access logs bypass the filter entirely.

Reproduction

from ray import serve
from ray.serve.schema import LoggingConfig

@serve.deployment(logging_config=LoggingConfig(enable_access_log=False))
class Hello:
    def __call__(self, request):
        return "hello"

serve.start(logging_config=LoggingConfig(enable_access_log=False))
serve.run(Hello.bind())

curl http://localhost:8000/

Expected: No access log lines in stderr.

Actual:

INFO 2026-02-07 ... -- CALL __call__ OK 0.3ms
INFO 2026-02-07 ... -- GET / 200 1.2ms

These lines appear in stderr despite enable_access_log=False being set at both deployment and global level.

Root Cause

In configure_component_logger() (ray/serve/_private/logging_utils.py), the log_access_log_filter is added to memory_handler (file handler) but never to stream_handler (stderr handler):

# stream_handler — no access log filter applied (BUG)
if RAY_SERVE_LOG_TO_STDERR or stream_handler_only:
    stream_handler = logging.StreamHandler()
    stream_handler.addFilter(log_to_stderr_filter)
    stream_handler.addFilter(ServeContextFilter())
    logger.addHandler(stream_handler)

# ...

# memory_handler — filter correctly applied
if logging_config.enable_access_log is False:
    memory_handler.addFilter(log_access_log_filter)

Fix

Add the same log_access_log_filter to the stream_handler when enable_access_log is False:

if RAY_SERVE_LOG_TO_STDERR or stream_handler_only:
    stream_handler = logging.StreamHandler()
    stream_handler.setFormatter(serve_formatter)
    stream_handler.addFilter(log_to_stderr_filter)
    stream_handler.addFilter(ServeContextFilter())
    if logging_config.enable_access_log is False:
        stream_handler.addFilter(log_access_log_filter)
    logger.addHandler(stream_handler)

A regression test (test_access_log_suppressed_in_stderr) is added to verify access logs are filtered from stderr while normal user logs still appear.

[gemini-code-assist]

Code Review

This pull request addresses a bug where access logs were not being suppressed on stderr when enable_access_log=False was specified in the logging configuration. The root cause was correctly identified as the log_access_log_filter not being applied to the stream_handler. The fix adds this filter to the stream_handler, which is consistent with the existing logic for the file-based memory_handler. The change is clear, targeted, and effectively resolves the issue. The accompanying explanation in the pull request description is excellent.

[harshit-anyscale]

can we extend this test to test both behaviors, that access log should be and shouldn't be generated based on enable_access_log?

[kouroshHakha]

kk.