How can I start one container before other?

Question

I need to start backend-container after start database-container. How can I do it with docker-compose?

Answer 1

Use a depends_on clause on your backend-container. Something like that :

version: "3.7"
services:
  web:
    build: .
    depends_on:
      - db
  db:
    image: postgres

Here is the documentation about it. Have fun!

Answer 2

You should look into the depends_on configuration for docker compose.

In short, you should be able to do something like:

services:
  database-container:
    # configuration
  backend-container:
    depends_on:
      - database-container
    # configuration

Answer 3

The depends_on field will work with docker-compose, but you will find it is not supported if you upgrade to swarm mode. It also guarantees the database container is created, but not necessarily ready to receive connections.

For that, there are several options:

• Let the backend container fail and configure a restart policy. This is ugly, leads to false errors being reported, but it's also the easiest to implement.
• Perform a connection from your app with a retry loop, a sleep between retries, and a timeout in case the database doesn't start in a timely fashion. This is usually my preferred method, but it requires a change to your application.
• Use an entrypoint script with a command like wait-for-it.sh that waits for a remote resource to become available, and once that command succeeds, launch your app. This doesn't cover all the scenarios as a complete client connection, but can be less intrusive to implement since it only requires changes to an entrypoint script rather than the app itself.