Database not persisting in docker

问题:

I know I am missing something very basic here. I have see some of the older questions on persisting data using docker, but I think I am following the most recent documentation found here. I have a rails app that I am trying to run in docker. It runs fine but every time I start it up i get ActiveRecord::NoDatabaseError. After I create the database and migrate it, the app runs fine, until I shut it down and restart it.

here is my docker file:

FROM ruby:2.3.0
RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs
ENV RAILS_ROOT /ourlatitude
RUN mkdir -p $RAILS_ROOT/tmp/pids
WORKDIR $RAILS_ROOT
COPY Gemfile Gemfile     
COPY Gemfile.lock Gemfile.lock
RUN gem install bundler     
RUN bundle install
COPY . .

and here is my docker-compose.yml file

version: '2'
services:
  db:
    image: postgres:9.4.5
  app:
    build: .
    environment:
      RAILS_ENV: $RAILS_ENV
  ports:
    - "3000:3000"
  command: bundle exec rails s -b 0.0.0.0
  volumes:
    - .:/ourlatitude/database
  depends_on:
    - db

the basic flow I am following is this:

export RAILS_ENV=development
docker-compose build
docker-compose up
docker-compose run app rake db:create
docker-compose run app rake db:migrate

at this point the app will be running fine

but then I do this

docker-compose down
docker-compose up

and then I am back to the ActiveRecord::NoDatabaseError

So as I said, I think I am missing something very basic.

回答1:

It doesn't look like you put your postgres on a volume, you may be missing other persistent data sources in your app container, and it appears you missed some indentation on your app container definition.

version: '2'
services:
  db:
    image: postgres:9.4.5
    volumes:
      - postgres-data:/var/lib/postgresql/data
  app:
    build: .
    environment:
      RAILS_ENV: $RAILS_ENV
    ports:
      - "3000:3000"
    command: bundle exec rails s -b 0.0.0.0
    volumes:
      - .:/ourlatitude/database
    depends_on:
      - db
volumes:
  postgres-data:
    driver: local

In the example above, the postgres data is stored in a named volume. See the advice on docker hub for more details on persisting data for that application. If you are still losing data, check the output of docker diff $container_id on a container to see what files are changing outside of your volumes that would be lost on a down/up.

回答2:

I managed to get this to work properly using the following docker-compose.yml file.

version: '2'
volumes:
  postgres-data:
services:
  db:
    image: postgres:9.4.5
    volumes:
      - postgres-data:/var/lib/postgresql/data
  app:
    build: .
    environment:
      RAILS_ENV: $RAILS_ENV
    ports:
      - "3000:3000"
    command: bundle exec rails s -b 0.0.0.0
    depends_on:
      - db

The key was to add the

volumes:
  postgres-data:

which creates the named volume and then the

volumes:
  - postgres-data:/var/lib/postgresql/data

under the db section which maps the named volume to the expected location in the container of /var/lib/postgresql/data