fix: add tini as init to reap Docker healthcheck zombie children

[DeliciousBuding]

Root cause

server-hub runs as PID 1 in the container (entrypoint exec). Docker healthcheck spawns wget -qO- http://localhost:8080/health every 30-90s inside the container PID namespace. When these children exit, Go runtime's SIGCHLD handler only reaps processes started via os/exec — not externally injected Docker healthcheck children.

Production evidence: ~150 wget zombies accumulated over 3 days on hk2, ~16 on us1. All with parent ./server-hub (PID 1).

Fix

Add tini as init (PID 1) via apk add tini + ENTRYPOINT tini -- entrypoint.sh. tini handles SIGCHLD and reaps all orphaned children — standard Docker best practice for non-C-native binaries.

Changes: 2 lines in Dockerfile only. Zero Go code changes.

• apk add --no-cache ... tini
• ENTRYPOINT ["/sbin/tini", "--", "/usr/local/bin/docker-entrypoint.sh"]

Closes #420

Summary by CodeRabbit

• Bug Fixes
  • Improved container startup and process handling for more reliable application shutdown and signal management.
  • Updated runtime setup to include the required initialization support.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: 7bcb97b1-b516-4bda-a86a-676d972e3436

📥 Commits

Reviewing files that changed from the base of the PR and between 65b22e2 and 2e03359.

📒 Files selected for processing (1)

• hub-server/deployments/Dockerfile

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📝 Walkthrough

Walkthrough

The runtime Docker image consolidates package installation, adds tini, updates the init-process comment, and changes container startup to invoke docker-entrypoint.sh through tini.

Changes

Runtime container initialization

Layer / File(s)	Summary
Install and wire tini hub-server/deployments/Dockerfile	The runtime stage installs tini with the existing packages and changes ENTRYPOINT to launch docker-entrypoint.sh through /sbin/tini.

Estimated code review effort: 1 (Trivial) | ~3 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The change only wraps the container with tini; it does not fix the wget spawn path or add Wait()/net/http healthchecks.	Update the server-hub code or healthcheck path so child processes are reaped with Wait()/Wait4, or replace shell-out wget checks with net/http.

✅ 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 matches the main change: adding tini as the container init process to reap zombie children.
Out of Scope Changes check	✅ Passed	The Dockerfile-only changes are aligned with the stated fix and do not introduce unrelated scope.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/server-hub-tini-zombie-reaper

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