Jenkins supports the master/agent architecture. In master/agent architecture, we can install Jenkins on master and then utilize other agents for distributing the load.

We shoulddelegate Jenkins jobs to agents for execution. This way, we can support multiple executions using different resources.

There are specific scenarios where master/agent architecture is extremely useful, such as following:

• The Jenkins machine has limited capacity; even with the higher capacity, there will be a time where it can't fulfil all requests. By distributing the load on agent nodes, we can free resources available on the system where Jenkins is installed.
• Different jobs require different kinds of resources, and they are restricted to specific machines only. In such a case, we can only utilize that machine and it is not possible to configure it on a system...

Can we execute a Jenkins job from Eclipse? Yes we can! So, let's see how to do that.

1. Go to Help | Install New Software...:

2. Add a site for Mylyn and click on Next >:

3. Review the items to be installed and click on Next >.
4. Accept the terms of the license agreement and then click on Finish. It will start installing the Mylyn package.
5. Once it is finished, Restart Eclipse.

Let's see how to trigger a Jenkins build from Eclipse.

1. In the Windows menu, click on Views.
2. Select Mylyn and...

A core task for the smooth running of Jenkins is the scheduled backing up of its home directory. This is not necessarily all the artifacts, but is at least its configuration and the history of testing, which plugins will need to make reports.

Backups are not interesting unless you can also restore. There is a wide range of stories on this subject. My favorite (and I won't name the well-known company involved) is that, sometime in the early 70's, a company bought a very expensive piece of software and a tape backup facility to back up all the marketing results being harvested through their mainframes. However, not everything was automated. Every night, a tape needed to be moved into a specific slot. A poorly paid worker was allocated the task. For a year, the worker would professionally fulfill the task. One day, a failure occurred and...

You can access various features in Jenkins through a command-line tool.

Download the Jenkins-cli.jar file from the link available on the Jenkins dashboard.

1. Go to the location where Jenkins-cli.jar is downloaded and execute the java -jar jenkins-cli.jar -s http://localhost:8080/ help command to see the help of CLI commands:

2. Execute the following commands:

java -jar jenkins-cli.jar -s http://localhost:8080/ version
java -jar jenkins-cli.jar -s http://localhost:8080/ who-am-i
java -jar jenkins...

You may well be wondering about the XML files at the top level of the Jenkins workspace. These are configuration files. The config.xml file is the main one that deals with the default server values, but there are also specific ones for any plugins that have values set through the GUI.

There is also a jobs subdirectory underneath the workspace. Each individual job configuration is contained in a subdirectory with the same name as the job. The job-specific configuration is then stored in config.xml within the subdirectory. It's a similar situation for the users directory: there is one subdirectory per user, with the personal information stored in config.xml.

Under a controlled situation where all the Jenkins servers in your infrastructure have the same plugins and version levels, it is possible for you to test on one...

Jenkins stores multiple jobs and the multiple builds created are stored on the machine. It is important to keep track of disk usage, as, over time, builds from multiple projects will take up a lot of space.

Go to Dashboard| Manage Jenkins|Manage Plugins|Available|Install Disk Usage plugin.

This plugin gives details on disk usage on the system where Jenkins is installed.

1. Go to Dashboard | Manage Jenkins | Disk Usage:

2. Go to Manage Jenkins and click on Configure System. Go to the Disk usage section and click on Show disk...

Is it possible to stop executing new builds so that the system can eventually be shut down safely? Let's find out in the following recipe.

You need to have administrative access to Jenkins.

1. Go to the Jenkins dashboard, then Manage Jenkins Prepare for Shutdown:

2. Go to the Jenkins dashboard again, then Manage Jenkins to Cancel Shutdown:

JavaMelody (http://code.google.com/p/javamelody/) is an open source project that provides comprehensive monitoring. The Jenkins plugin monitors both the master instance of Jenkins and also its nodes. The plugin provides a detailed wealth of important information. You can view evolution charts ranging from 1 day or 1 week to months for the main quantities, such as CPU or memory. Evolution charts are very good at pinpointing scheduled jobs that are resource-hungry.

The Monitoring plugin provides the monitoring of Jenkins with JavaMelody. It provides charts for CPU, memory, system load average, HTTP response time, and so on. It also provides details of HTTP sessions, errors and logs, actions for garbage collection, heap dumps, invalid session(s), and so on.

The Build Monitor plugin provides a visualization of the status and progress of selected Jenkins jobs. It displays an updated view automatically every couple of seconds using AJAX. It can easily accommodate different computer screen sizes too.

Go to Manage Jenkins | Manage Plugins | Available tab. Install the Build Monitor View plugin:

Go to the Jenkins dashboard.

1. Click on New View:

2. Provide View name and select Build Monitor View. Click OK:

3. Select...

How about sending a mail notification when a build is successful or fails?

It is essential to know when something fails so that we can take corrective measures at the right time. You need to have an email account to configure email notifications in Jenkins and SMTP details.

1. Go to Manage Jenkins and go to the E-mail Notification section. Provide all the necessary details based on the email account:

2. In the build job where you want to configure mail notifications, go to Post-build Actions and select E-mail Notification...

Each development team is unique. Teams have their own way of doing business. In many organizations, there are one-off tasks that need to be done periodically. For example, at the end of each year, making a full backup of the entire filesystem.

This recipe details a script that checks for the last successful run of any job; if the year is different to the current year, then a warning is set at the beginning of the job's description. Thus, it is hinting to you that it's time to perform an action, such as archiving and then deleting. You can of course programmatically do the archiving. However, for high-value actions, it is worth forcing interceding, letting the Groovy scripts focus your attention.