Docker Container Networking with Docker-in-Docker

问题

I would like to network with a child docker container from a parent docker container, with a docker-in-docker setup.

Let's say I'm trying to connect to a simple Apache httpd server. When I run the httpd container on my host machine, everything works fine:

asnyder:~$ docker run -d -p 8080:80 httpd:alpine
asnyder:~$ curl localhost:8080
<html><body><h1>It works!</h1></body></html>

But when I do the same from a docker-in-docker setup, I get a Connection refused error:

asnyder:~$ docker run -d --name mydind --privileged docker:dind
asnyder:~$ docker run -it --link mydind:docker docker:latest sh
/ # docker run -d -p 8080:80 httpd:alpine
/ # curl localhost:8080
curl: (7) Failed to connect to localhost port 8080: Connection refused

I have tried a couple alterations without luck. Specifying the 0.0.0.0 interface:

asnyder:~$ docker run -d --name mydind --privileged docker:dind
asnyder:~$ docker run -it --link mydind:docker docker:latest sh
/ # docker run -d -p 0.0.0.0:8080:80 httpd:alpine
/ # curl 0.0.0.0:8080
curl: (7) Failed to connect to 0.0.0.0 port 8080: Connection refused

Using the host network:

asnyder:~$ docker run -d --name mydind --privileged docker:dind
asnyder:~$ docker run -it --link mydind:docker docker:latest sh
/ # docker run -d --network host httpd:alpine
/ # curl localhost:80
curl: (7) Failed to connect to localhost port 80: Connection refused

Surprisingly, I was unable to find any existing articles on this. Does anyone here have some insight?

Thanks!

回答1:

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!

回答2:

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

回答3:

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>

来源：https://stackoverflow.com/questions/44830663/docker-container-networking-with-docker-in-docker

标签

networking

Docker

docker-in-docker