• Created by magnayn -, last modified by Nico Schmoigl on Mar 04, 2017

Plugin Information

This plugin allows slaves to be dynamically provisioned using Docker.

Background

The aim of the docker plugin is to be able to use a docker host to
dynamically provision a slave, run a single build, then tear-down that
slave.

Optionally, the container can be committed, so that (for example)
manual QA could be performed by the container being imported into a
local docker provider, and run from there.

Setup

A quick setup is :

- get a docker environment running

- follow the instructions for creating a system that has an ssh server installed, and a JDK

- create a user (e.g: jenkins) that you can log in with

- store that image with a known ID (e.g: jenkins) so that it appears in the output of "docker images" command

Docker Environment

Follow the installation steps on docker.io.

If your host needs to allow connections from a jenkins instance
hosted on a different machine, you will need to open up the TCP port.
This can be achieved by editing the docker config file and setting (for
example)

The docker configuration file location will depend your system, but
it is likely to be /etc/init/docker.conf, /etc/default/docker
or /etc/default/docker.io)

Creating a docker image

Shortcut : Pulling a Docker image

You can pull a ready-made jenkins slave! (Use at your own risk.)

You need a docker image that has, as a minimum, an ssh server
installed. You probably want a JDK, and you will also want a 'jenkins'
user that can log in. Example session to do this:

root@Quordlepleen:/etc/init# docker pull ubuntu

Pulling repository ubuntu

...

root@Quordlepleen:/etc/init# docker run -i -t ubuntu /bin/bash

root@cff9f1f868b0:/# apt-get update

root@cff9f1f868b0:/# apt-get install openssh-server

root@cff9f1f868b0:/# mkdir /var/run/sshd

root@cff9f1f868b0:/# apt-get install openjdk-6-jdk

root@cff9f1f868b0:/# adduser jenkins

Adding user `jenkins' ...

Adding new group `jenkins' (1000) ...

Adding new user `jenkins' (1000) with group `jenkins' ...

Creating home directory `/home/jenkins' ...

Copying files from `/etc/skel' ...

Enter new UNIX password:

Retype new UNIX password:

passwd: password updated successfully

Changing the user information for jenkins

Enter the new value, or press ENTER for the default

Full Name []: Jenkins

Room Number []:

Work Phone []:

Home Phone []:

Other []:

Is the information correct? [Y/n] Y

root@cff9f1f868b0:/# /usr/sbin/sshd

root@cff9f1f868b0:/# exit

Once the container has been created, you need to commit it with a name to be used later, e.g: jenkins-1

root@Quordlepleen:/etc/init# docker ps -a

CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES

cff9f1f868b0        ubuntu:12.04        /bin/bash           7 minutes ago       Exit 0                                  goofy_mccarthy    

root@Quordlepleen:/etc/init# docker commit cff9f1f868b0 jenkins-1

9ebe455d911904ce0939b41758af6b3159b91ccb0aa36e7bc911d96c8cc30e64

root@Quordlepleen:/etc/init# docker images

REPOSITORY          TAG                 IMAGE ID            CREATED             VIRTUAL SIZE

jenkins-1           latest              9ebe455d9119        3 minutes ago       422.1 MB

ubuntu              saucy               43461fe97ba1        5 days ago          144.6 MB

ubuntu              raring              5e94ff221e91        5 days ago          133.6 MB

ubuntu              quantal             3e47bae8d07a        5 days ago          127.6 MB

ubuntu              lucid               04180f9bd8a6        5 days ago          139.6 MB

ubuntu              precise             1e548c932d40        5 days ago          125.9 MB

ubuntu              12.04               8dbd9e392a96        9 months ago        128 MB

ubuntu              latest              8dbd9e392a96        9 months ago        128 MB

ubuntu              12.10               b750fe79269d        10 months ago       175.3 MB

cff9f1f868b0        ubuntu:12.04        /bin/bash           7 minutes ago       Exit 0                                  goofy_mccarthy     

You may wish to periodically update your build image -- e.g: if you are using maven, then it would be advantageous to update your local maven repository with released artifacts, to prevent having to download them again (and thus speeding up your builds).

Tips

It is very easy to update your jenkins image in docker -

root@krikkit:~# docker run -i -t jenkins-1 /bin/bash

# HACK ON IMAGE

root@d0ba389c07c5:/home/jenkins# exit

# Save new image

root@krikkit:~# docker commit d0ba389c07c5 jenkins-2

By default, the docker plugin will execute /usr/sbin/sshd -D, therefore it is not recommended that you set the ENTRYPOINT unless you plan to pass extra arguments from Jenkins

Configuration

Docker appears in the 'Cloud' section of the Jenkins configuration, select "Docker" from the "Add a new cloud" drop down menu.

The docker cloud configuration has the following options:

Images:

Click the Add button to add a new image.

The docker cloud configuration has the following options:

Job Configuration

Container Cap and Instance Capacity

Container cap and instance capacity both limits the number of
containers this plugin requests to be running on the Docker server at a
time. They serve a different purpose, but are very similar in general.
Thus, their difference may be hard to understand.

• The container cap is an "overall limit", which restricts the number
  of containers which may be running -- irrespectively which image is
  being used.
• The instance capacity is limiting the number of containers for a given image only.

Here's an example, which should make it clearer:

Let us assume that

• the container cap is set to 10,
• the instance capacity of image A is set to 6, and
• the instance capacity of image B is set to 5.

Let 5 containers of image A and 5 containers of image B be running on
the Docker server. Even though there is still one slot free of capacity
for image A, no new container will be provision: The container cap for
the Docker Host is already reached.

Let us assume that the container cap is changed to 12. Now, another
container can be provisioned for image A, as the instance capacity is
not reached yet. However, that does not hold true for image B, as the
instance capacity is set to 5 and already 5 containers are running.

Triton and Container Cap / Instance Capacity

If your Docker server is running Triton, be aware of the fact that -
in contrast to the Docker reference implementation - containers are
private to the user you are using to log on.
This implies the effect that the container cap and the instance capacity
is calculate relative to the user only and is not applied globally
(which can be a good or a bad thing, depending on your use case).

Known Issues

If you have trouble selecting "Docker" from the clouds list, then you need to update your credentials plugin.

Changelog

See https://github.com/jenkinsci/docker-plugin/blob/master/CHANGELOG.md