Jenkins on Mesos
The jenkins-mesos plugin allows Jenkins to dynamically launch Jenkins slaves on a
Mesos cluster depending on the workload!
Put simply, whenever the Jenkins Build Queue starts getting bigger, this plugin
automatically spins up additional Jenkins agent(s) on Mesos so that jobs can be
immediately scheduled! Similarly, when a Jenkins slave is idle for a long time it
is automatically shut down.
Table of Contents
Prerequisite
You need to have access to a running Mesos cluster. For instructions on setting up a Mesos cluster, please refer to the Mesos website.
Installing the Plugin
-
Go to 'Manage Plugins' page in the Jenkins Web UI, you'll find the plugin in the 'Available' tab under the name 'mesos'.
-
(Optional) Install the metrics plugin which is an optional dependency of this plugin, used for additional but not essential features.
Configuring the Plugin
Now go to 'Configure' page in Jenkins. If the plugin is successfully installed
you should see an option to 'Add a new cloud' at the bottom of the page.
- Add the 'Mesos Cloud'.
- Give the path to the address
http://HOST:PORTof a running Mesos master. On DC/OS this can be as simple ashttps://leader.mesos:5050. - Set the user name agents should start as. Ensure that the Mesos agents have have the user available.
- Set the Jenkins URL.
- Click
Save.
You can click Test Conection to see if the Mesos client of the plugin can find the Mesos master.
If the Mesos master uses a secured connection with a custom certificate you can supply it under
Use a custom SSL certificate.
Adding Agent Specs
An Agent Spec describes a Jenkins node for Mesos.
You can update the values/Add more 'Agent Specs'/Delete 'Agent Specs' by clicking on 'Advanced'.
'Agent Specs' can hold required information(Executor CPU, Executor Mem etc) for an agent that needs
to be matched against Mesos offers.
Label name is the key between the job and the required agent to execute the job. See Configuring Jenkins Jobs.
For instance, heavy jobs can be assigned label 'powerful_agent'(which has 20 Executor CPU, 10240M Executor Mem etc)
and light weight jobs can be assigned label 'light_weight_agent'(which has 1 Executor CPU, 128M Executor Mem etc).
The Jenkins Configuration as Code in dcos/conf/jenkins configures a Linux agent based on the amazoncorretto:8 Docker image and a Windows agent based on mesosphere/jenkins-windows-node:latest Docker image. See https://github.com/jeschkies/hello-world-fsharp/blob/master/Jenkinsfile for an example build.
DC/OS Authentication
The plugin can authenticate with a DC/OS enterprise cluster.
Simply run the environment variables DCOS_SERVICE_ACCOUNT containing the service account name and
DCOS_SERVICE_ACCOUNT_PRIVATE_KEY containing the private key for the service account. See On DC/OS Enterprise for details.
Configuring Jenkins Jobs
Finally, just add the label name you have configured in Mesos cloud configuration -> Advanced -> Slave Info -> Label String (default is mesos)
to the jobs (configure -> Restrict where this project can run checkbox) that you want to run on a specific slave type inside Mesos cluster.
Docker Containers
By default, the Jenkins slaves are run in the default Mesos container. To run the Jenkins agent inside a Docker container, there are two options.
1) "Use Native Docker Containerizer" : Select this option if Mesos slave(s) are configured with "--containerizers=docker" (recommended).
2) "Use External Containerizer" : Select this option if Mesos slave(s) are configured with "--containerizers=external".
Docker Configuration
Volumes
At a minimum, a container path must be entered to mount the volume. A host path can also be specified to bind mount the container path to the host path. This will allow persistence of data between slaves on the same node. The default setting is read-write, but an option is provided for read-only use.
Parameters
Additional parameters are available for the docker run command, but there are too many and they change too often to list all separately. This section allows you to provide any parameter you want. Ensure that your Docker version on your Mesos slaves is compatible with the parameters you add and that the values are correctly formatted. Use the full-word parameter and not the shortcut version, as these may not work properly. Also, exclude the preceding double-dash on the parameter name. For example, enter volumes-from and my_container_name to recieve the volumes from my_container_name. Of course my_container_name must already be on the Mesos slave where the Jenkins slave will run. This shouldn't cause problems in a homogenous environment where Jenkins slaves only run on particular Mesos slaves.
Over provisioning flags
By default, Jenkins spawns slaves conservatively. Say, if there are 2 builds in queue, it won't spawn 2 executors immediately. It will spawn one executor and wait for sometime for the first executor to be freed before deciding to spawn the second executor. Jenkins makes sure every executor it spawns is utilized to the maximum.
If you want to override this behaviour and spawn an executor for each build in queue immediately without waiting, you can use these flags during Jenkins startup:
-Dhudson.slaves.NodeProvisioner.MARGIN=50 -Dhudson.slaves.NodeProvisioner.MARGIN0=0.85
Single-Use Slave
Freestyle jobs
In the Build Environment settings, you may select "Mesos Single-Use Slave" to schedule disposal of the slave after the build finishes.
Pipeline jobs
To schedule slave disposal from a Pipeline job:
node('mylabel') {
wrap([$class: 'MesosSingleUseSlave']) {
// build actions
}
}
Plugin Development
Building the plugin
Build the plugin as follows:
$ ./gradlew check
This should build the Mesos plugin as mesos.hpi in the target folder. A test Jenkins server can be
started with
$ ./gradlew server
The code is formatted following the Google Style Guide.
Testing On DC/OS Enterprise
See the dcos folder.
Release
You must have publish rights and the credentials set in ~/.m2/settings.xml and ~/.jenkins-ci.org as described
here.
To release this plugin
- Set the version in
build.gradle. - Publish the plugin with
./gradlew publish.