Announce: public Jenkins CI server

1 Aug 2016 Emanuel Borsboom

We have set up a new public Jenkins CI server for use with our open source projects. This server currently runs the Stack integration tests, and deploys to and every time a commit is pushed to the master branch of their respective repositories.

In the future, we also intend to set up Jenkins to run the Stack integration tests on all supported platforms (rather than only Linux) using additional Jenkins workers, and get it to run them for pull requests as well.

While we use Travis CI, there are a couple of ways it does not meet our needs that Jenkins helps us with:

  • For long builds, we hit the 50 minute job timeout. While a standard series of tests should not exceed this amount of time, we also want to run more exhaustive integration tests which sometimes take longer. We can let Travis run the standard tests on PRs, and then periodically run the more extensive tests on Jenkins.

  • Some projects need to build Docker images. While Travis does support this, it means enabling the "standard" (non container-based) environment for jobs, which in turn does not support caching builds for public projects. For Haskell projects in particular, working without a cache means very long build times.

  • Projects also need to push Docker images to a registry and deploy them to a Kubernetes cluster. This requires exposing credentials to builds, which is impossible to secure when building code that uses TemplateHaskell, which allows running arbitrary code during the build.

For these projects, we continue to use Travis for quick feedback on PRs, but let Jenkins take care of the integration tests and deployments where we need more control over resource limitations and isolation of different build phases.

We run all the builds and tests on ephemeral, isolated Jenkins workers using the Docker plugin. These workers do not have access to any credentials, so there is no risk of credentials "leaking" into build logs or otherwise being accessed inappropriately.

For projects that need auto-deployment, the isolated build job stages the assets to be deployed, and then a separate deploy job is triggered if the build is successful. The deploy job runs on the Jenkins master which has access to required credentials, but it does not check out the project's source code from Github or run anything developer-provided. It only copies the built artifacts from the upstream job, builds and pushes a Docker image, and then updates a Kubernetes Deployment with the new image. Our public Jenkins server does not ever see any credentials for proprietary repos or mission-critical infrastructure, so even if security is breached it will have no effect beyond the CI system itself.

For production deployments of open source applications, we have a separate private Jenkins server that builds from the prod branch of the Git repositories, and deploys to a separate cluster. We ensure that the prod branch is protected so that only project administrators can trigger a production deployment.

We avoid using too many Jenkins-specific features. Essentially, we use Jenkins to perform triggering, notification and provide the build environment, but don't use Jenkins plugins to build Docker images or perform deployments. The Jenkins Docker plugin could commit an image after building and testing the code, but then we would have large images containing the whole build environment rather than minimal images containing only the application to deploy. We prefer instead to leave it to our own custom tooling that we can tailor to our needs and which can be run in many different environments so that we are not locked into Jenkins. A developer with access to the right credentials could, if necessary, perform the process easily from their own workstation by running the same build and deploy scripts as the Jenkins jobs run.

The Jenkins servers themselves run on EC2, with all cloud infrastructure managed using Hashicorp's Terraform, and the instances managed using Red Hat's Ansible. The Kubernetes cluster is set up using CoreOS's kube-aws tool.

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