Better Jenkins Notifications in Declarative Pipelines

I’ve been using declarative pipelines in Jenkins for a while with the Slack plugin to send build notifications to Slack. The plugin does what it says on the tin but gives you a pretty boring message by default.

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I used the environment variables available in the pipeline to make things a little bit better and link back to the job.

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But I was still always disappointed the notifications didn’t contain more information. Thankfully version 2.3 of the plugin added support for the attachments portion of the Slack message API. I was able to leverage the attachments feature to get better message formatting. Meanwhile, I took some inspiration from this thread to incorporate test result summaries.

I store this in a shared pipeline library to avoid repeating the code in every Jenkinsfile. This way you can simply call it in a post step like this.

post {
always {
notifySlack currentBuild.result
}
}

Here is the code in the pipeline library

The end result is a much more informative message.

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Jenkins Dynamic EC2 Slaves

There is a nice plugin for Jenkins that lets you dynamically add capacity by spinning up EC2 instances on demand and then terminating them when the job queue expires. This is a great way to save money on an AWS based build infrastructure.

Unfortunately, the plugin documentation is really light and there are a few gotchas to look out for.

Security Groups

This field only accepts comma separated security group IDs, not names. This is frustrating because other fields in the plugin take a space separated list (e.g. labels)

Running in VPC

If you’re a sane person you’re going to want to run these instances in a private VPC. This is entirely possible but is hidden in the advanced settings. If you expand the advanced settings you’ll see a field to enter your desired subnet ID. Set this to the ID of the private subnet in your VPC you want the instances to run in.

Don’t Rely On the User Data/Init Scrip to Install Dependencies

This adds a lot of time to the instance coming on line and being usable by Jenkins. A better approach is to make an AMI with all the build dependencies you need. The only delay is then the instance boot time.

This is far from an exhaustive walkthrough but highlights the issues I ran into setting it up.