fix(obs): disable profiling export by default and fix Helm env name

[houseme]

Type of Change

• New Feature
• Bug Fix
• Documentation
• Performance Improvement
• Test/CI
• Refactor
• Other:

Related Issues

#2715

Summary of Changes

Problem

When RUSTFS_OBS_ENDPOINT is set but the Pyroscope/OTel collector endpoint is
unreachable, the profiling export background task accumulates data indefinitely.
After 2-3 days of idle (no bucket traffic) this eventually triggers an extremely
large allocation request (memory allocation of 2267059503403440 bytes failed)
and causes the process to abort.

Root cause

DEFAULT_OBS_PROFILING_EXPORT_ENABLED was true, meaning any deployment that
set an OTLP root endpoint automatically activated the Pyroscope profiling export
path on Linux/macOS — even when no Pyroscope endpoint was reachable or intended.
Additionally, the Helm chart emitted RUSTFS_OBS_PROFILING_ENABLED (wrong name)
instead of RUSTFS_OBS_PROFILING_EXPORT_ENABLED, so the intended false value
in the chart was silently ignored and the runtime default (true) took effect.

Changes

1. crates/config/src/constants/app.rs

   • DEFAULT_OBS_PROFILING_EXPORT_ENABLED: true → false.
   • Updated constant doc comment to match.

2. crates/obs/src/config.rs

   • Added backward-compatible read_profiling_export_enabled() that recognises
     the legacy alias RUSTFS_OBS_PROFILING_ENABLED (as emitted by older Helm
     charts) so existing deployments with RUSTFS_OBS_PROFILING_ENABLED=true
     continue to work without a config change.
   • Priority: RUSTFS_OBS_PROFILING_EXPORT_ENABLED > RUSTFS_OBS_PROFILING_ENABLED

     hardcoded default (false).

   • Added 3 targeted tests covering default, legacy alias, and precedence.

3. helm/rustfs/templates/configmap.yaml

   • Fixed env var name: RUSTFS_OBS_PROFILING_ENABLED → RUSTFS_OBS_PROFILING_EXPORT_ENABLED.

4. crates/obs/README.md

   • Updated RUSTFS_OBS_PROFILING_EXPORT_ENABLED default column from true → false.

Migration notes

• Deployments that relied on profiling being enabled by default must now
  explicitly set RUSTFS_OBS_PROFILING_EXPORT_ENABLED=true (or the legacy
  alias) and ensure a reachable RUSTFS_OBS_PROFILING_ENDPOINT.
• Deployments using the Helm chart: this fix makes the chart's existing
  profiling.enabled: false default actually take effect (previously it was
  silently ignored due to the wrong env var name).

Checklist

• I have read and followed the CONTRIBUTING.md guidelines
• Passed make pre-commit
• Added/updated necessary tests
• Documentation updated (if needed)
• CI/CD passed (if applicable)

Impact

• Breaking change (compatibility)
  • Backward-compatible: the old alias RUSTFS_OBS_PROFILING_ENABLED is still
    accepted. Only the default changes (off instead of on).
• Requires doc/config/deployment update
  • Operators who want profiling must now opt in explicitly.
• Other impact:

Additional Notes

Verification steps used during development:

cargo test -p rustfs-obs profiling_export_
cargo test -p rustfs-obs canonical_profiling_toggle_has_priority_over_legacy_alias

All 3 tests pass.

[github-actions]

CLA requirements are satisfied for this pull request.

[Copilot]

Pull request overview

Disables Pyroscope profiling export by default to prevent unbounded profile buffering/allocations when the collector endpoint is unreachable, and aligns Helm/config/docs with the corrected env-var behavior.

Changes:

• Flip DEFAULT_OBS_PROFILING_EXPORT_ENABLED from true to false.
• Add backward-compatible env handling for the legacy RUSTFS_OBS_PROFILING_ENABLED toggle (with tests) and update docs.
• Fix Helm chart to emit the correct env var name for profiling export enablement.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
crates/config/src/constants/app.rs	Changes the default profiling export toggle to disabled (false).
crates/obs/src/config.rs	Adds legacy env alias support + tests; wires new helper into config extraction.
helm/rustfs/templates/configmap.yaml	Renames Helm-emitted env var to RUSTFS_OBS_PROFILING_EXPORT_ENABLED.
crates/obs/README.md	Updates documented default for profiling export to false.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

[Copilot]

The README’s “Routing Logic” section earlier states that any OTLP endpoint implies a “Full OTLP/HTTP pipeline (… + profiling)”. With RUSTFS_OBS_PROFILING_EXPORT_ENABLED now defaulting to false, that statement is no longer accurate—profiling export requires an explicit opt-in. Please update the routing logic text to reflect the new default/opt-in behavior to avoid operator confusion.

[Copilot]

The PR description mentions adding a read_profiling_export_enabled() helper, but the implementation here directly calls get_env_bool_with_aliases(...) inline. Either update the PR description to match the actual implementation or add the helper as described (if that was the intent) to keep the change log accurate.