Enhance healthcheck blocking dependent behavior like lifecyle

[loynoir]

Description

Problem

I found postgres image can't block dependent startup, which make dependent start up too early.

Actual

If dependent accept client at early time, dependent failed.

Expected

After postgres ready, dependent should not startup and accept client.

Try

• Add /docker-entrypoint-initdb.d/wait.sh, which does not block dependent.

• Overwrite command, which does not block dependent.

• Besides, when overwrite entry/command, sometimes you may need to know what is the original entry/command, and call these HARD CODED command in a very ugly way.

• https://stackoverflow.com/questions/31746182/docker-compose-wait-for-container-x-before-starting-y

I found .depends_on.X.condition works, but not very graceful to solve wait-for-container-x-before-starting-y.

• If .interval big, run .healthcheck.test late, startdependent late, not very ideal.

• If .interval small, run .healthcheck.test too many times, not very graceful.

Workaround

Below is my workaround.

  foo:
    ...
    depends_on:
      bar:
        condition: service_healthy
    ...
 
  bar:
    ...
    tmpfs:
      - /tmp
    healthcheck:
      test: 'if [ -e /tmp/first_run ]; then sleep 24h; else touch /tmp/first_run; bash /script/wait.sh; fi'
      timeout: 25h
      interval: 1s

Feat

Above workaround I still don't think very ideal, so I opened a feat.

Enhance healthcheck behavior like lifecyle.

  foo:
    ...
    depends_on:
      bar:
        condition: service_lifecycle_bootstrap
    ...
 
  bar:
    ...
    lifecycle:
        bootstrap: 'bash /script/wait.sh'

Related

• Execute a command after run #1809

• Proposal: docker-compose events #1510

Additional

Are there lifecyle support within container ecosystem?

Yes, vscode devcontainer support lifecycle.

https://github.com/devcontainers/spec/blob/main/schemas/devContainerFeature.schema.json#L106-L206

• initializeCommand
• onCreateCommand
• updateContentCommand
• postCreateCommand
• postStartCommand
• postAttachCommand

[ndeloof]

the devcontainer feature you're listing here is about command hooks to run during container lifecycle, not about dependency management.

IIUC your needs, you have to wait for postgres to be running and accept connexion before your client code get started, otherwise connexion fails. This is exactly what condition: service_healthy is designed for: client container won't get started before their dependency is reported as "healthy" by the container runtime, which is easy to setup as postgres ilmage includes utility tool pg_isready.

healthcheck interval and health status unfortunately is managed by container runtime, not docker compose, so we can't tweak the interval to avoid unnecessary runs once service is started
AFAICT you're looking for readyness check which isn't supported by docker engine (see moby/moby#30860) - maybe we should introduce this feature directly in Docker Compose