page_title: Work with a development container
page_description: How to use Docker's development environment
page_keywords: development, inception, container, image Dockerfile, dependencies, Go, artifacts
# Work with a development container
In this section, you learn to develop like a member of Docker's core team.
The `docker` repository includes a `Dockerfile` at its root. This file defines
Docker's development environment. The `Dockerfile` lists the environment's
dependencies: system libraries and binaries, go environment, go dependencies,
etc.
Docker's development environment is itself, ultimately a Docker container.
You use the `docker` repository and its `Dockerfile` to create a Docker image, run a Docker container, and develop code in the container. Docker itself builds, tests, and releases new Docker versions using this container.
If you followed the procedures that set up the prerequisites, you should have a fork of the
`docker/docker` repository. You also created a branch called `dry-run-test`. In this section, you continue working with your fork on this branch.
## Clean your host of Docker artifacts
Docker developers run the latest stable release of the Docker software; Or Boot2docker and Docker if their machine is Mac OS X. They clean their local hosts of unnecessary Docker artifacts such as stopped containers or unused images. Cleaning unnecessary artifacts isn't strictly necessary but it is good practice, so it is included here.
To remove unnecessary artifacts.
1. Verify that you have no unnecessary containers running on your host.
$ docker ps
You should see something similar to the following:
| CONTAINER ID |
IMAGE |
COMMAND |
CREATED |
STATUS |
PORTS |
NAMES |
There are no running containers on this host. If you have running but unused
containers, stop and then remove them with the `docker stop` and `docker rm`
commands.
2. Verify that your host has no dangling images.
$ docker images
You should see something similar to the following:
| REPOSITORY |
TAG |
IMAGE ID |
CREATED |
VIRTUAL SIZE |
This host has no images. You may have one or more _dangling_ images. A
dangling image is not used by a running container and is not an ancestor of
another image on your system. A fast way to remove dangling containers is
the following:
$ docker rmi -f $(docker images -q -a -f dangling=true)
This command uses `docker images` to lists all images (`-a` flag) by numeric
IDs (`-q` flag) and filter them to find dangling images (`-f
dangling=true`). Then, the `docker rmi` command forcibly (`-f` flag) removes
the resulting list. To remove just one image, use the `docker rmi ID`
command.
## Build an image
If you followed the last procedure, your host is clean of unnecessary images and containers. In this section, you build an image from the Docker development environment.
1. Open a terminal.
Mac users, use `boot2docker status` to make sure Boot2Docker is running. You
may need to run `$(boot2docker shellinit)` to initialize your shell
environment.
3. Change into the root of your forked repository.
$ cd ~/repos/docker-fork
4. Ensure you are on your `dry-run-test` branch.
$ git checkout dry-run-test
5. Compile your development environment container into an image.
$ docker build -t dry-run-test .
The `docker build` command returns informational message as it runs. The
first build may take a few minutes to create an image. Using the
instructions in the `Dockerfile`, the build may need to download source and
other images. A successful build returns a final status message similar to
the following:
Successfully built 676815d59283
6. List your Docker images again.
$ docker images
You should see something similar to this:
| REPOSTITORY |
TAG |
IMAGE ID |
CREATED |
VIRTUAL SIZE |
| dry-run-test |
latest |
663fbee70028 |
About a minute ago |
|
| ubuntu |
trusty |
2d24f826cb16 |
2 days ago |
188.3 MB |
| ubuntu |
trusty-20150218.1 |
2d24f826cb16 |
2 days ago |
188.3 MB |
| ubuntu |
14.04 |
2d24f826cb16 |
2 days ago |
188.3 MB |
| ubuntu |
14.04.2 |
2d24f826cb16 |
2 days ago |
188.3 MB |
| ubuntu |
latest |
2d24f826cb16 |
2 days ago |
188.3 MB |
Locate your new `dry-run-test` image in the list. You should also see a
number of `ubuntu` images. The build process creates these. They are the
ancestors of your new Docker development image. When you next rebuild your
image, the build process reuses these ancestors images if they exist.
Keeping the ancestor images improves the build performance. When you rebuild
the child image, the build process uses the local ancestors rather than
retrieving them from the Hub. The build process gets new ancestors only if
DockerHub has updated versions.
## Start a container and run a test
At this point, you have created a new Docker development environment image. Now,
you'll use this image to create a Docker container to develop in. Then, you'll
build and run a `docker` binary in your container.
1. Open two additional terminals on your host.
At this point, you'll have about three terminals open.
Mac OSX users, make sure you run `$(boot2docker shellinit)` in any new
terminals.
2. In a terminal, create a new container from your `dry-run-test` image.
$ docker run --privileged --rm -ti dry-run-test /bin/bash
root@5f8630b873fe:/go/src/github.com/docker/docker#
The command creates a container from your `dry-run-test` image. It opens an
interactive terminal (`-ti`) running a `/bin/bash shell`. The
`--privileged` flag gives the container access to kernel features and device
access. It is this flag that allows you to run a container in a container.
Finally, the `-rm` flag instructs Docker to remove the container when you
exit the `/bin/bash` shell.
The container includes the source of your image repository in the
`/go/src/github.com/docker/docker` directory. Try listing the contents to
verify they are the same as that of your `docker-fork` repo.
3. Investigate your container bit.
If you do a `go version` you'll find the `go` language is part of the
container.
root@31ed86e9ddcf:/go/src/github.com/docker/docker# go version
go version go1.4.2 linux/amd64
Similarly, if you do a `docker version` you find the container
has no `docker` binary.
root@31ed86e9ddcf:/go/src/github.com/docker/docker# docker version
bash: docker: command not found
You will create one in the next steps.
4. From the `/go/src/github.com/docker/docker` directory make a `docker` binary with the `make.sh` script.
root@5f8630b873fe:/go/src/github.com/docker/docker# project/make.sh binary
You only call `project/make.sh` to build a binary _inside_ a Docker
development container as you are now. On your host, you'll use `make`
commands (more about this later).
As it makes the binary, the `make.sh` script reports the build's progress.
When the command completes successfully, you should see the following
output:
---> Making bundle: ubuntu (in bundles/1.5.0-dev/ubuntu)
Created package {:path=>"lxc-docker-1.5.0-dev_1.5.0~dev~git20150223.181106.0.1ab0d23_amd64.deb"}
Created package {:path=>"lxc-docker_1.5.0~dev~git20150223.181106.0.1ab0d23_amd64.deb"}
5. List all the contents of the `binary` directory.
root@5f8630b873fe:/go/src/github.com/docker/docker# ls bundles/1.5.0-dev/binary/
docker docker-1.5.0-dev docker-1.5.0-dev.md5 docker-1.5.0-dev.sha256
You should see that `binary` directory, just as it sounds, contains the
made binaries.
6. Copy the `docker` binary to the `/usr/bin` of your container.
root@5f8630b873fe:/go/src/github.com/docker/docker# cp bundles/1.5.0-dev/binary/docker /usr/bin
7. Inside your container, check your Docker version.
root@5f8630b873fe:/go/src/github.com/docker/docker# docker --version
Docker version 1.5.0-dev, build 6e728fb
Inside the container you are running a development version. This is version
on the current branch it reflects the value of the `VERSION` file at the
root of your `docker-fork` repository.
8. Start a `docker` daemon running inside your container.
root@5f8630b873fe:/go/src/github.com/docker/docker# docker -dD
The `-dD` flag starts the daemon in debug mode; You'll find this useful
when debugging your code.
9. Bring up one of the terminals on your local host.
10. List your containers and look for the container running the `dry-run-test` image.
$ docker ps
| CONTAINER ID |
IMAGE |
COMMAND |
CREATED |
STATUS |
PORTS |
NAMES |
| 474f07652525 |
dry-run-test:latest |
"hack/dind /bin/bash |
14 minutes ago |
Up 14 minutes |
|
tender_shockley |
In this example, the container's name is `tender_shockley`; yours will be
different.
11. From the terminal, start another shell on your Docker development container.
$ docker exec -it tender_shockley bash
At this point, you have two terminals both with a shell open into your
development container. One terminal is running a debug session. The other
terminal is displaying a `bash` prompt.
12. At the prompt, test the Docker client by running the `hello-world` container.
root@9337c96e017a:/go/src/github.com/docker/docker# docker run hello-world
You should see the image load and return. Meanwhile, you
can see the calls made via the debug session in your other terminal.
## Restart a container with your source
At this point, you have experienced the "Docker inception" technique. That is, you have:
* built a Docker image from the Docker repository
* created and started a Docker development container from that image
* built a Docker binary inside of your Docker development container
* launched a `docker` daemon using your newly compiled binary
* called the `docker` client to run a `hello-world` container inside your development container
When you really get to developing code though, you'll want to iterate code
changes and builds inside the container. For that you need to mount your local
Docker repository source into your Docker container. Try that now.
1. If you haven't already, exit out of BASH shells in your running Docker
container.
If you have followed this guide exactly, exiting out your BASH shells stops
the running container. You can use the `docker ps` command to verify the
development container is stopped. All of your terminals should be at the
local host prompt.
2. Choose a terminal and make sure you are in your `docker-fork` repository.
$ pwd
/Users/mary/go/src/github.com/moxiegirl/docker-fork
Your location will be different because it reflects your environment.
3. Create a container using `dry-run-test` but this time mount your repository onto the `/go` directory inside the container.
$ docker run --privileged --rm -ti -v `pwd`:/go/src/github.com/docker/docker dry-run-test /bin/bash
When you pass `pwd`, `docker` resolves it to your current directory.
4. From inside the container, list your `binary` directory.
root@074626fc4b43:/go/src/github.com/docker/docker# ls bundles/1.5.0-dev/binary
ls: cannot access binary: No such file or directory
Your `dry-run-test` image does not retain any of the changes you made inside
the container. This is the expected behavior for a container.
5. In a fresh terminal on your local host, change to the `docker-fork` root.
$ cd ~/repos/docker-fork/
6. Create a fresh binary but this time use the `make` command.
$ make BINDDIR=. binary
The `BINDDIR` flag is only necessary on Mac OS X but it won't hurt to pass
it on Linux command line. The `make` command, like the `make.sh` script
inside the container, reports its progress. When the make succeeds, it
returns the location of the new binary.
7. Back in the terminal running the container, list your `binary` directory.
root@074626fc4b43:/go/src/github.com/docker/docker# ls bundles/1.5.0-dev/binary
docker docker-1.5.0-dev docker-1.5.0-dev.md5 docker-1.5.0-dev.sha256
The compiled binaries created from your repository on your local host are
now available inside your running Docker development container.
8. Repeat the steps you ran in the previous procedure.
* copy the binary inside the development container using
`cp bundles/1.5.0-dev/binary/docker /usr/bin`
* start `docker -dD` to launch the Docker daemon inside the container
* run `docker ps` on local host to get the development container's name
* connect to your running container `docker exec -it container_name bash`
* use the `docker run hello-world` command to create and run a container inside your development container
## Where to go next
Congratulations, you have successfully achieved Docker inception. At this point, you've set up your development environment and verified almost all the essential processes you need to contribute. Of course, before you start contributing, [you'll need to learn one more piece of the development environment, the test framework](/project/test-and-docs/).