Docker Container Networking with Docker-in-Docker

There are pros and cons for both DinD and bind mounting the Docker socket and there are certainly use cases for both. As an example, check out this set of blog posts, which does a good job of explaining one of the use cases.

Given your example docker-in-docker setup above, you can access Apache httpd server in one of two ways:

1) From inside the docker:dind container, it will be available on localhost:8080.

2) From inside the docker:latest container, where you were trying to access it originally, it will be available on whatever hostname is set for the docker:dind container. In this case, you used --name mydind, therefore curl mydind:8080 would give you the standard Apache <html><body><h1>It works!</h1></body></html>.

Hope it makes sense!


Building upon Yuriy's answer:

2) From inside the docker:latest container, [...] it will be available on whatever hostname is set for the docker:dind container. In this case, you used --name mydind, therefore curl mydind:8080 [...]

In the Gitlab CI config, you can address the DinD container by the name of its image (in addition to the name of its container, which is auto-generated):

Accessing the services

Let’s say that you need a Wordpress instance to test some API integration with your application.

You can then use for example the tutum/wordpress image in your .gitlab-ci.yml:

services:
- tutum/wordpress:latest

If you don’t specify a service alias, when the job is run, tutum/wordpress will be started and you will have access to it from your build container under two hostnames to choose from:

  • tutum-wordpress
  • tutum__wordpress

Using

service:
- docker:dind

will allow you to access that container as docker:8080:

  script:
  - docker run -d -p 8080:80 httpd:alpine
  - curl docker:8080

Edit: If you'd prefer a more explicit host name, you can, as the documentation states, use an alias:

services:
- name: docker:dind
  alias: dind-service

and then

  script:
  - docker run -d -p 8080:80 httpd:alpine
  - curl dind-service:8080

Hth, dtk


I am very convinced that @Yuriy Znatokov's answer is what I want, but I have understood it for a long time. In order to make it easier for later people to understand, I have exported the complete steps.

1) From inside the docker:dind container

docker run -d --name mydind --privileged docker:dind
/ # docker run -d -p 8080:80 httpd:alpine
/ # curl localhost:8080
<html><body><h1>It works!</h1></body></html>

2) From inside the docker:latest container

docker run -d --name mydind --privileged docker:dind
docker run -it --link mydind:docker docker:latest sh
/ # docker run -d -p 8080:80 httpd:alpine
/ # curl mydind:8080
<html><body><h1>It works!</h1></body></html>

Tags:

Docker

Networking

Docker In Docker

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