Jenkins Slave on EC2

Our Jenkins master running on an AWS t1.micro has run out of memory for running the more complex integration tests e.g. play server, mongodb, headless X and firefox. Rather than have the cost of a larger instance all the time when pushes to version control are occasional (cough) we will run a slave for these tests that only costs when there's a test to run. A simple JUnit run through can still work on the master. The Jenkins Amazon EC2 plugin makes this easy, and handles temporary instances.
This install a lot like the earlier post on creating the master, so I'll skip most of the screenshots, but fix a few things too:

1. On the master, stop all the extra services (databases, X etc) running with service and chkconfig. That leaves more memory for basic compile / unit test cycles and fewer potential holes for a site that needs to be up all the time.
2. Create a new 64bit instance which deletes its root filesystem on termination. Auto-delete is much cheaper than tidying up manually. I went with a 10GB filesystem.The 64bit install means that there are some x86_64 in place of earlier i686 choices. The firewall need only open ssh as this is what Jenkins uses.
3. Do the package installations and a first start / stop pass for each and a manual git list, to get the first time prompts out of the way. Generally I'm accepting all the defaults here and using the default filesystem layout. I try to keep the package order the same as on the master, so that UIDs match between the two and make sure ec2-user and/or jenkins own the necessary files.
   

   sudo yum update
   sudo ln -sf /usr/share/zoneinfo/Europe/London /etc/localtime
   sudo yum install erlang
   wget http://www.rabbitmq.com/releases/rabbitmq-server/v3.1.3/rabbitmq-server-3.1.3-1.noarch.rpm
   sudo yum install rabbitmq-server-3.1.3-1.noarch.rpm
   sudo service rabbitmq-server start
   sudo service rabbitmq-server stop
   
   sudo yum install mysql mysql-server mysql-libs
   sudo service mysqld start
   /usr/bin/mysql_secure_installation
   sudo service mysqld stop
   sudo yum install mysql-connector-java
   
   yum search java | grep 'java-'
   sudo yum install java-1.7.0-openjdk.x86_64
   sudo alternatives --config java 
   
   
   sudo yum install tomcat7-lib.noarch tomcat7-servlet-3.0-api.noarch tomcat7.noarch
   
   sudo wget -O /etc/yum.repos.d/jenkins.repo http://pkg.jenkins-ci.org/redhat/jenkins.repo
   sudo rpm --import http://pkg.jenkins-ci.org/redhat/jenkins-ci.org.key
   sudo yum install jenkins
   sudo mkdir /var/jenkins-slave
   sudo chown ec2-user:jenkins /var/jenkins-slave/
   
   cd /etc/yum.repos.d
   sudo vi 10gen.repo
   cat 10gen.repo
   cat 10gen.repo
   [10gen]
   name=10gen Repository
   baseurl=http://downloads-distro.mongodb.org/repo/redhat/os/x86_64
   gpgcheck=0
   enabled=1
   sudo yum install mongo-10gen mongo-10gen-server
   sudo service mongo start
   sudo service mongo stop
   
   cd
   wget http://downloads.typesafe.com/play/2.1.2/play-2.1.2.zip
   cd /usr/local
   sudo unzip ~/play-2.1.2.zip
   sudo chown -R ec2-user:jenkins /usr/local/play-2.1.2/
   /usr/local/play-2.1.2/play test
   
   sudo yum install ant ant-junit
   
   sudo yum install git
   
   ssh-keygen -t rsa -C "jenkins@aws"
   cat .ssh/id_rsa.pub
   // add the key to Assembla's list of keys in your profile
   git ls-remote -h git@git.assembla.com:projectname.git HEAD
   
   sudo yum install Xvfb
   cd
   vi ./gtk-firefox
   insert the code from http://joekiller.com/2012/06/03/install-firefox-on-amazon-linux-x86_64-compiling-gtk/
   chmod 755 ./gtk-firefox
   sudo ./gtk-firefox
   // do something else for a bit  
   

4. Stop the EC2 instance and create an AMI of it.

Now, the slave can be set up in Jenkins. First, install the Amazon EC2 plugin. Then use the global configuration to set up the slave's properties. The idle termination time of 30 means it has time to boot, run some tests and get shut down within a one hour billing time. I also use this for starting services on the slave:

Then, in the job configuration use the "Restrict where this project can be run" choice to add the label for that slave. Jobs requiring different services can have additional AMIs defined under the Jenkins global config. Note that you can have multiple AMIs under Jenkins point to the same AMI image on AWS, which may reduce the number of EC2 configurations to be maintained.

If you're at all unsure about the config it doesn't hurt to do a test cycle by hand: pull from git, compile, test and tidy up.