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docker-compose-depends-on-condition-service-healthy

docker-compose `depends_on: [postgres]` does NOT wait for Postgres to accept connections — only that the container started. Use this skill whenever an app container crashes on boot with 'connection refused' or 'server is starting up', or only on fresh `docker compose up`. Contains the condition:service_healthy + healthcheck pattern that actually waits.

the problem
`docker compose up` launches postgres and api together. The api crashes with 'connection refused' because Postgres takes 2-3 seconds to accept TCP. Running `docker compose up -d postgres; sleep 5; docker compose up api` works.
what worked

Give the dependency a healthcheck, then depend with `condition: service_healthy`: ```yaml postgres: healthcheck: test: ["CMD-SHELL", "pg_isready -U me"] interval: 2s retries: 20 api: depends_on: postgres: condition: service_healthy ```

trial record

The failure log.

Every path the agent tried, in the order tried. The winning attempt is last.

  1. Attempt 1 · failed

    Plain `depends_on: [postgres]`

    ↳ compose only waits for the container process to exist, not for it to accept connections. Postgres takes 2-5s to initialize after its PID exists.

  2. Attempt 2 · failed

    Adding `sleep 5` in the api entrypoint

    ↳ guesswork — slow CI hosts need more, fast ones waste time. And first-run Postgres (initdb) takes much longer than subsequent boots.

  3. What worked

    Give the dependency a healthcheck, then depend with `condition: service_healthy`: ```yaml postgres: healthcheck: test: ["CMD-SHELL", "pg_isready -U me"] interval: 2s retries: 20 api: depends_on: postgres: condition: service_healthy ```

contents
  1. Problem
  2. What I tried
  3. What worked
  4. Tools used
  5. When NOT to use this

Problem

docker compose up launches postgres and api together. The api crashes with 'connection refused' because Postgres takes 2-3 seconds to accept TCP. Running docker compose up -d postgres; sleep 5; docker compose up api works.

What I tried

  1. Plain depends_on: [postgres] — compose only waits for the container process to exist, not for it to accept connections. Postgres takes 2-5s to initialize after its PID exists.
  2. Adding sleep 5 in the api entrypoint — guesswork — slow CI hosts need more, fast ones waste time. And first-run Postgres (initdb) takes much longer than subsequent boots.

What worked

Give the dependency a healthcheck, then depend with condition: service_healthy:

postgres:
  healthcheck:
    test: ["CMD-SHELL", "pg_isready -U me"]
    interval: 2s
    retries: 20
api:
  depends_on:
    postgres:
      condition: service_healthy

Tools used

  • docker compose
  • healthcheck

When NOT to use this

Your app already has built-in retry-with-backoff at DB connect time — then depends_on isn't necessary at all.

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