[Core]Add env var to disable log_monitor stdout/stderr file redirection

Start in ray/_private/logging_utils.py at the log_monitor StreamRedirector calls and trace the existing tee_to_stdout and tee_to_stderr parameters. Verify that RAY_LOG_MONITOR_TEE_STDOUT=1 reaches both redirect calls while unset or non-1 preserves current behavior; done means output is duplicated to terminal and log files without changes to Cython or C++.

Description

Environment

• Ray version: 2.58.0
• Deployment: KubeRay on Kubernetes
• Related code path: Python (logging_utils.py) → Cython (_raylet.pyx StreamRedirector) → C++ (stream_redirector.cc RedirectStdoutOncePerProcess)

Problem

log_monitor.py redirects stdout/stderr to log files on startup via StreamRedirector. The underlying Cython binding already supports tee_to_stdout and tee_to_stderr parameters, but they are hardcoded to False in ray/_private/logging_utils.py, making it impossible for users to enable tee mode (output to both file and terminal) without patching source code.

Proposed Solution

Add environment variable RAY_LOG_MONITOR_TEE_STDOUT=1. When set, log_monitor's output is written to both log files and stdout/stderr simultaneously.

Proposed Change in ray/_private/logging_utils.py

tee_enabled = os.environ.get("RAY_LOG_MONITOR_TEE_STDOUT", "0") == "1"

if stdout_filepath:
StreamRedirector.redirect_stdout(
stdout_filepath, rotation_bytes, rotation_backup_count,
tee_enabled, # tee_to_stdout (currently hardcoded False)
tee_enabled, # tee_to_stderr (currently hardcoded False)
)
if stderr_filepath:
StreamRedirector.redirect_stderr(
stderr_filepath, rotation_bytes, rotation_backup_count,
tee_enabled,
tee_enabled,
)

The change is minimal — one env var read, two False replacements. No C++ or Cython changes needed.

Use case

We run Ray on Kubernetes via KubeRay, and use a sidecar-based log collector (Fluentd/Loki) to aggregate all container stdout/stderr into our centralized logging platform.

When RAY_LOG_MONITOR_TEE_STDOUT=1:

log_monitor's output is written to both log files on disk and stdout/stderr. Log files remain available for debugging via container filesystem, and the sidecar log collector can simultaneously capture all output through the standard container log pipeline.

When RAY_LOG_MONITOR_TEE_STDOUT is unset or not equal to 1 (default, unchanged):

log_monitor redirects its stdout/stderr to log files only. No output reaches stdout/stderr.