How to wait until `docker start` is finished?

Question

When I run docker start, it seems the container might not be fully started at the time the docker start command returns. Is it so?

Is there a w

Answer 1

A common technique to make sure a container is fully started (i.e. services running, ports open, etc) is to wait until a specific string is logged. See this example Waiting until Docker containers are initialized dealing with PostgreSql and Rails.

Edited:

There could be another solution using the HEALTHCHECK of Docker containers.The idea is to configure the container with a health check command that is used to determine whether or not the main service if fully started and running normally.

The specified command runs inside the container and sets the health status to starting, healthy or unhealthy depending of its exit code (0 - container healthy, 1 - container is not healthy). The status of the container can then be retrieved on the host by inspecting the running instance (docker inspect).

Health check options can be configured inside Dockerfile or when the container is run. Here is a simple example for PostgreSQL

 docker run --name postgres --detach \
  --health-cmd='pg_isready -U postgres' \
  --health-interval='5s' \
  --health-timeout='5s' \
  --health-start-period='20s' \
  postgres:latest && \
  until docker inspect --format "{{json .State.Health.Status }}" postgres| \
  grep -m 1 "healthy"; do sleep 1 ; done

In this case the health command is pg_isready. A web service will typically use curl, other containers have their specific commands The docker community provides this kind of configuration for several official images here

Now, when we restart the container (docker start), it is already configured and we need only the second part:

docker start postgres && \
until docker inspect --format "{{json .State.Health.Status }}" postgres|\ 
grep -m 1 "healthy"; do sleep 1 ; done

The command will return when the container is marked as healthy

Hope that helps.