docker-compose rails app doesn't find db when using up but does when doing run

Question

I have a simple Rails application that I'm trying to run using Docker. When I run docker-compose up it runs but when I load a page it tells me that my db doesn't exist. Even though when I run docker-compose run app rails db:create it says that the db already exists.

docker-compose.yml

version: '2'

services:
  db:
    image: postgres 
  app:
    build: ./rails
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - ./app:/app
    ports:
      - "3000:3000"
    depends_on:
      - db

./rails/Dockerfile

FROM ruby:2.3.3
RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs
RUN mkdir /app
WORKDIR /app
ADD ./Gemfile /app/Gemfile
ADD ./Gemfile.lock /app/Gemfile.lock
RUN bundle install

I'm new to Docker so I may be missing something basic.

In my experience, the database usually takes some time to be usable. As an experiment, try wrapping your command in a shell script that sleeps 10 seconds before running your rails server command. — Rickkwa
– Rickkwa, Commented Dec 10, 2016 at 18:44

user988558user988558 · Accepted Answer · 2018-01-17 04:25:41Z

0

Rickkwa is correct, db takes some time to get stable.

You could potentially work around the issue by having a Ruby script with the following:

begin
  retries ||= 0
  Mysql2::Client.new(host: 'db', username: 'root')
rescue
  sleep 1
  retry if (retries += 1) < 10
end

answered Jan 17, 2018 at 4:25

user988558

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