Docker Compose：允许图像访问主机资源（如postgresql）

Question

Our infrastructure uses Docker containers to separate our services. I'm beginning to set up our docker-compose to aid in local development.

Some of our services use the Ruby on Rails framework, and developing locally for that is quickest by running the server and database locally (traditional Rails development).

To more closely mimic the production environment, docker-compose would be useful. Our database is not ephemeral (are they ever :P) and thus we don't run them as docker containers.

Given that, how can I construct my docker-compose to allow the Rails container to connect to the host's database (Postgresql in this case)? There are a lot of data in the local database that would be useful in smoke-testing the application.

Answer 1

I guess you don't want to access the host's IP address inside the server container manually.

What you can use is extra_hosts and export the hosts IP address as an environment variable:

service:
  image: alpine:3.4
  extra_hosts:
    - "host:${HOST_IP}"
  command: cat /etc/hosts

Unfortunately docker-compose does not support something like "host:$(ip -4 addr show ...)" . So for this to work each developer must edit their .bashrc (or whatever they are using).

On my machine this gives me the correct local IP address:

ip -4 addr show|grep brd|egrep -o 'inet ([0-9]+\.){3}[0-9]+'|cut -d ' ' -f2

Alternative :

Or you could just configure the database to listen on the docker0 interface as well and edit your docker-compose.yml to look like this:

service:
  image: alpine:3.4
  extra_hosts:
    - "host:172.17.0.1"
  command: cat /etc/hosts

Answer 2

The best way to do this would be to run the database in a container.

database is not ephemeral and thus we don't run them as docker containers.

This statement is incorrect. You can run a database in a Docker container. Just make sure you use a volume to store the data in a well known directory on the host. That way if the database stops, it will come back up with the same data.

Once you have the database in a container it is very easy to connect to it from other containers.