how to start postgres prior to run docker

debugcn 投稿 Dev

David Pekker

I am super embarrassed to ask this question, because it seems a very basic one, but somehow I can't find the answer in docs.

I have a django app that uses postgres. In docker-compose.yaml there is the following requirement:

version: "2"

services:

database:
  image: postgres:9.5
  environment:
    POSTGRES_DB: ${POSTGRES_DATABASE}
    POSTGRES_USER: ${POSTGRES_USER}
    POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
    POSTGRES_DATA: /var/lib/postgresql/data/pgdata

when I run my docker image: docker run -it --name myapp myimage it keeps repeating:

The database is not ready.
wait for postgres to start...

I ran postgres in detached mode: docker run -it -d postgres:9.5 but it does not help

Krzysztof Atłasik

Please have a look at this doc.

Second example is exacly what you need:

You create sh script and add it to your app container by using ADD or COPY:

#!/bin/bash
# wait-for-postgres.sh

set -e

host="$1"
shift
cmd="$@"

until psql -h "$host" -U "postgres" -c '\l'; do
  >&2 echo "Postgres is unavailable - sleeping"
  sleep 1
done

>&2 echo "Postgres is up - executing command"
exec $cmd

Then you modify your docker-compose.yaml like this:

version: "2"
services:
  web:
    build: .
    ports:
      - "80:8000"
    depends_on:
      - "db"
    command: ["./wait-for-postgres.sh", "db", "python", "app.py"]
  db:
    image: postgres

In command you're orerriding default command of your container. Of course "python", "app.py" part is depedent on how you start your app. Fo Java it would be for example "java", "-jar", "my-app.jar" etc.

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