Docker wait for postgresql to be running

Question

I am using postgresql with django in my project. I've got them in different containers and the problem is that i need to wait for postgres before running django. At this time i am doing it with sleep 5 in command.sh file for django container. I also found that netcat can do the trick but I would prefer way without additional packages. curl and wget can't do this because they do not support postgres protocol. Is there a way to do it?

Answer 1

I've spent some hours investigating this problem and I got a solution. Docker depends_on just consider service startup to run another service. Than it happens because as soon as db is started, service-app tries to connect to ur db, but it's not ready to receive connections. So you can check db health status in app service to wait for connection. Here is my solution, it solved my problem. :) Important: I'm using docker-compose version 2.1.

version: '2.1'  services:   my-app:     build: .     command: su -c "python manage.py runserver 0.0.0.0:8000"     ports:        - "8000:8000"     depends_on:       db:         condition: service_healthy     links:       - db     volumes:       - .:/app_directory    db:     image: postgres:10.5     ports:       - "5432:5432"     volumes:       - database:/var/lib/postgresql/data     healthcheck:       test: ["CMD-SHELL", "pg_isready -U postgres"]       interval: 5s       timeout: 5s       retries: 5  volumes:   database: 

In this case it's not necessary to create a .sh file. I hope it helps you guys ;) cya

Answer 2

This will successfully wait for Postgres to start. (Specifically line 6). Just replace npm start with whatever command you'd like to happen after Postgres has started.

services:   practice_docker:      image: dockerhubusername/practice_docker     ports:        - 80:3000     command: bash -c 'while !</dev/tcp/db/5432; do sleep 1; done; npm start'     depends_on:       - db     environment:       - DATABASE_URL=postgres://postgres:password@db:5432/practicedocker       - PORT=3000      db:     image: postgres     environment:       - POSTGRES_USER=postgres       - POSTGRES_PASSWORD=password       - POSTGRES_DB=practicedocker