# Docker Health Check Patterns Quick reference for adding health checks to Docker containers. ## Basic: curl (requires curl in image) ```dockerfile HEALTHCHECK --interval=30s --timeout=5s --retries=3 \ CMD curl -f http://localhost:3000/health || exit 1 ``` ## Better: wget (available in Alpine) ```dockerfile HEALTHCHECK --interval=30s --timeout=5s --retries=3 \ CMD wget --no-verbose --tries=1 --spider http://localhost:3000/health || exit 1 ``` ## Best for Node.js: native HTTP check (no extra binaries) ```dockerfile HEALTHCHECK --interval=30s --timeout=5s --start-period=40s --retries=3 \ CMD node -e "require('http').get('http://localhost:3000/health', (r) => { process.exit(r.statusCode === 200 ? 0 : 1) }).on('error', () => process.exit(1))" ``` Works in `node:slim` and `node:alpine` without installing curl or wget. ## Production: dedicated script with dependency checks ```bash #!/bin/sh # healthcheck.sh wget -q --spider http://localhost:3000/health || exit 1 if ! pg_isready -h localhost -p 5432 > /dev/null 2>&1; then exit 1 fi if [ -n "$REDIS_URL" ]; then redis-cli -u "$REDIS_URL" ping > /dev/null 2>&1 || exit 1 fi exit 0 ``` ## Key parameters | Parameter | Default | Recommendation | |-----------|---------|----------------| | `--interval` | 30s | 30s for most apps | | `--timeout` | 30s | 5-10s (fail fast) | | `--start-period` | 0s | **Set this!** 30-60s for apps that need warmup | | `--retries` | 3 | 3 is fine | ## Common mistakes - **Forgetting `--start-period`** — container gets killed during startup - **Using `curl` in slim images** — use wget or Node.js native instead - **Not checking dependencies** — app is "healthy" but database is down - **Too short timeout** — intermittent failures cause unnecessary restarts
Version 3·Updated Apr 2, 2026·View-only
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