Lab 1: Reduce the cost of builds using Amazon EC2 Spot Fleet

The Jenkins server that was launched by the CloudFormation template has a number of build projects preconfigured. However by default, all builds will be executed on the same instance that Jenkins is running on. This results in a couple of less-than-desirable behaviours: * When CPU-intensive builds are being executed, there may not be sufficient system resources to display the Jenkins server interface; and * The Jenkins server is often provisioned with more resources than the server interface requires in order to allow builds to execute. When builds are not being executed, these server resources are essentially going to waste.

To address these behaviours, Jenkins provides the capability to execute builds on external hosts (called build agents). Further, AWS provides a Jenkins plugin to allow Jenkins to scale out a fleet of EC2 instances in order to execute build jobs on. This lab will focus on implementing EC2 Spot build agents, showcasing what a batch processing workload typically looks like when using Amazon EC2 Spot instances.

PROVISION A SPOT FLEET FOR YOUR BUILD AGENTS

Before configuring the EC2 Fleet Jenkins Plugin, create a Spot Fleet that will be used by the plugin to perform your application builds. As this is a batch processing use case, remember the best practices for this type of workload - leverage per-second billing (catered for through the use of an Amazon Linux AMI defined in the Launch Template); optimize for lowest cost; determine job completion and retry failed jobs (the former is handled by the Jenkins EC2 Fleet plugin); and be instance flexible.

  1. Go to the EC2 console and click on the Spot Requests option from the left frame (or click here);
  2. Click on the Request Spot Instances button;
  3. At the first screen of the Spot instance launch wizard:
    1. Under the Tell us your application or task need heading, ensure that the Load balancing workloads option selected (Note: do NOT select the Flexible workloads option as this will deploy a Spot Fleet with weightings applied to some of the EC2 instance types which will adversely impact how the plugin scales out);
    2. In the Configure your instances section, select the JenkinsBuildAgentLaunchTemplate template from the Launch template dropdown (if this option is not present in the dropdown, please verify that the CloudFormation template that you launched during the Workshop Preparation has deployed successfully). Change the Network to be the Spot CICD Workshop VPC. After making this selection, enable the check boxes for all three Availability Zones and then select the Amazon EC2 Spot CICD Workshop Public Subnet associated with each availability zone as the subnet to launch instances in;
    3. At the Tell us how much capacity you need section, keep the Total target capacity at 1 instance and the Optional On-Demand portion set to 0, and then tick the Maintain target capacity checkbox. Once selected, leave the Interruption behavior set to Terminate;
    4. While the new Spot Instances wizard makes some good recommendations to you on how best to add diversity to the fleet that you’re creating, the recommended instance types provide more resources than we strictly need in this workshop - so to the right of the Fleet request settings heading, clear the tick from Apply recommendations checkbox. Click on each of the Remove links associated with the all of the instance types initially defined to remove them from the fleet configuration. Then click on the Select instance types button and add the t2.medium, t2.large, t3.medium and t3.large instance types to the fleet definition (Hint: you may need to adjust the vCPUs and Memory (GiB) filters to reveal all of these instance types). Once the checkboxes for the required instance types have been ticked, click on the Select button. Once you have the four desired instance types listed in the fleet request, select the Lowest Price Fleet allocation strategy (since we’re interested in keeping cost to an absolute minimum for this use case);
    5. Review the Your fleet request as a glance section - it should indicate that your Fleet strength is Strong as a result of being able to draw instances from 12 instance pools, and your Estimated price should indicate that you’re expecting to make a 70% saving compared to the cost of equivalent on-demand resources;
    6. Lastly, click on the Launch button.
  4. Make a note of the Request ID of the Spot Fleet that you’ve just created.

CREATE A SECRET KEY AND ACCESS KEY FOR THE PLUGIN

The CloudFormation template that you deployed in Lab 1 created an IAM User called SpotCICDWorkshopJenkins. Jenkins will use this IAM User to control the spot fleet used for your build slaves. Generate a secret key and access key for this user.

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SIGN IN TO YOUR JENKINS SERVER

The CloudFormation template deployed during the Workshop Preparation stage deployed a Jenkins server on to an on-demand instance within your VPC and configured an Application Load Balancer (ALB) to proxy requests from the public Internet to the server. You can obtain the DNS name for the ALB from the Output tab of your CloudFormation template. Point your web browser to this DNS name and sign in using spotcicdworkshop as the Username and the password that you supplied to the CloudFormation template as the password.

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CONFIGURE THE EC2 FLEET JENKINS PLUGIN

The EC2 Fleet Jenkins Plugin was installed on the Jenkins server during the CloudFormation deployment - but now the plugin needs to be configured. You’ll first need to supply the IAM Access Key ID and Secret Key that you created so that the plugin can find your Spot Fleet request. You’ll then need to get the plugin to Launch slave agents via SSH and provide valid SSH credentials (don’t forget to consider how Host Key Verification should be set when using Spot instances).

When configuring the plugin, think about how you could force build processes to run on the spot instances (use the spot-agents label), and consider how you can verify that the fleet scales out when there is a backlog of build jobs waiting to be processed.

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RECONFIGURE YOUR BUILD JOBS TO USE THE NEW SPOT INSTANCE(S)

As alluded to in the previous section, you’ll need to reconfigure your build jobs so that they are executed on the build agents running in your Spot fleet (again, use the spot-agents label). In addition, configure each job to execute concurrent builds if necessary - this will help you in testing the scale-out of your fleet.

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TEST SPOT BUILDS AND SCALE-OUT

Now it’s time to test out how Jenkins handles pushing builds to spot instances running build agents at scale. There are two things that you’ll want to verify here; that your builds run successfully on the Spot instances, and that your Spot Fleet scales out when there are build jobs queued for more than a few minutes.

  1. Back at the Jenkins home page, first click on the ENABLE AUTO REFRESH link that’s located towards to top-right corner of the screen - this will enable a full refresh of the Jenkins user interface every 10 seconds allowing you to see regular updates to the status of each build. Next, click on the Schedule a Build icon (which looks like a play symbol superimposed over a clock) for each of the five Apache projects, starting from the Apache PDFBox project and working upward. This will queue up five build jobs, the first of which will be immediately assigned to the Spot instance to be worked on;
  2. When any of the build jobs have been completed, click on the Schedule a Build icon corresponding to that job to re-add it back to the build queue - the intent here is to keep the build queue populated with a backlog of build jobs until your Spot Fleet has scaled out and build jobs are executing on both Spot instances;
  3. After a couple of minutes (typically during the first Apache Helix build - around four minutes after you initiate the first build), the EC2 Fleet Status reported to the left of the screen will increment the target count to 2, indicating that the plugin has requested a scale-out action from the plugin. After a few moments, a second build instance will appear in the Build Executor Status, though this build agent will initially appear to be offline. Once the instance has had the chance to complete the launch and bootstrapping processes (which takes around two minutes), your Jenkins Master will deploy the build agent to it via SSH, and it will come online and process the next build job in the queue. Once you have concurrent builds being executed on two Spot instances, you can stop adding build jobs to the build queue;
  4. After a period of around a five minutes after your builds have completed, one of the Spot instances should be terminated by the plugin - there’s no need to wait for this to happen (take our word for it, but you can verify this later).

PROCEED TO LAB 2

Once you’ve verified that builds are succeeding and that your Spot Fleet is capable of scaling out to handle queued build jobs, you may proceed with Lab 2.