Jenkins Docker 插件

• 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:

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

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 -

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