wait_for_port is a simple container to do one thing: wait until a specified container is listening on a port.

If the port is 5432, it also attempts to log in to Postgres with the given credentials, since Postgres can be listening on port 5432 but still not yet really ready to serve requests.

Examples

docker run --rm --name wfp -v /var/run/docker.sock:/var/run/docker.sock \
    wait_for_port \
    --container somecontainer \
    --port 12345 \
    --timeout 10

Run the container and wait for container somecontainer to start listening on port 12345. Time out after 10 seconds.

docker run --rm --name wfp -v /var/run/docker.sock:/var/run/docker.sock \
    wait_for_port \
    --container somedbcontainer \
    --port 5432 \
    --timeout 100 \
    --pg_database "$POSTGRES_DB" \
    --pg_user "$POSTGRES_USER" \
    --pg_password "$POSTGRES_PASSWORD"

Run the container and wait for container somedbcontainer to start listening on port 5432 and accept the credentials to connect to the database. Time out after 100 seconds.

Use-Case

When using crane (or docker-compose, or similar), use a post-start hook to ensure a container is started after the container(s) it depends on is/are listening for incoming connections.

containers:
  slowstartingcontainer:
    build: {...}
    image: company.org/slowstartingcontainer
    run: {...}

  dependentcontainer:
    build: {...}
    image: company.org/dependentcontainer
    run:
      ...
      link:
        - slowstartingcontainer
      ...

hooks:
  slowstartingcontainer:
    post-start: "docker run --rm --name wfp -v /var/run/docker.sock:/var/run/docker.sock wait_for_port:latest --container slowstartingcontainer --port=12345 --timeout=3600"