Building GitHub projects on Jenkins slaves on OpenShift

This post showed how to build GitHub projects with Jenkins, Maven and SonarQube 4 on OpenShift. For starters, it used the Jenkins master node for running build jobs. However, when running on a small gear, the master node might run out of memory pretty fast, resulting in a reboot of the node during builds.

In order to resolve this issue, there are two options:

limitting the memory of the build or
running the build on a slave node.

As spawning additional nodes is easy in a PaaS context such as OpenShift and provides a better performance than running builds with small memory, the slave solution seems to be the better approach.

This post shows how.

Create new DYI app as a slave node (a how-to can be found here), name the node e.g. slave
Create node in Jenkins
1. Go to Jenkins web UI and create new node:
```
https://jenkins-.rhcloud.com/computer/new
```
2. Set the following values:
  Remote FS root:/app-root/data folder on slave. Typically this is /var/lib/openshift//app-root/data/jenkins, you can find out by SSHing to the slave node and calling
```
echo $OPENSHIFT_DATA_DIR/app-root/data/jenkins
```
  Labels: Some label to use within builds to refer the node, e.g. OS Slave #1
  Host: the slave’s hostname, e.g. slave-.rhcloud.com
3. Add Credentials
  username:
  Private Key File:Path to a private key file that is authorized for your OpenShift account. In the <a href="https://itaffinity.wordpress.com/2015/02/26/building-github-projects-with-jenkins-maven-and-sonarqube-4-1-1-on-openshift/”>first post this path was used: /var/lib/openshift//app-root/data/git-ssh/id_rsa. Note: $OPENSHIFT_DATA_DIR seems not to work here.
  BTW: You can change the credentials any time later via this URL
```
https://jenkins-.rhcloud.com/credentials/
```
Prepare slave node: Create same environment as on master in the <a href="https://itaffinity.wordpress.com/2015/02/26/building-github-projects-with-jenkins-maven-and-sonarqube-4-1-1-on-openshift/”>first post
1. Create folder structure
```
mkdir $OPENSHIFT_DATA_DIR/jenkins
mkdir $OPENSHIFT_DATA_DIR/.m2
echo -e "<settings><localRepository>$OPENSHIFT_DATA_DIR/.m2</localRepository></settings>" > $OPENSHIFT_DATA_DIR/.m2/settings.xml
```
2. Copy SSH directory from master to same directory on slave, e.g.
```
scp -rp -i $OPENSHIFT_DATA_DIR/.ssh $OPENSHIFT_DATA_DIR/.ssh <slave's UID>@slave-<your account>.rhcloud.com:app-root/data/.ssh
```
3. As the different cartridges (jenkins and DIY) have different environment variables for their local IP addresses ($OPENSHIFT_JENKINS_IP vs $OPENSHIFT_DIY_IP) we’ll have to improvise at this point. There are two options: Either
  1. Replace all occurrences of $OPENSHIFT_JENKINS_IP
    In all builds and in
```
https://jenkins-.rhcloud.com/configure
```
    Sonar | Sonar installations
    Database URL: jdbc:postgresql://$OPENSHIFT_DIY_IP:15555/sonarqube
    or
  2. Create an $OPENSHIFT_JENKINS_IP environment variable on your slave machine
```
rhc env set OPENSHIFT_JENKINS_IP=<value of  $OPENSHIFT_DIY_IP> -a slave
```
    You can find out the value of $OPENSHIFT_DIY_IP by SSHing to the slave and execute
```
echo $OPENSHIFT_DIY_IP 
```
  3. I’d love to hear suggesstions that do better 😉
Adapt Build
Easiest way is to not use the master at all.
To do so, go to
```
https://jenkins-.rhcloud.com/configure
```
and set # of executors to 0.
Hit Apply
Limit memory usage.
Make sure the slave does not run out of memory (which leads to a restart of the node):
Global properties | Environment variables
name: MAVEN_OPTS
value: -Xmx512m
Hit Save.
Now run a build. It should run on the slave and hopefully succeed 🙂