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Linux Containers

Linux Containers

Cirrus CI supports container and arm_container instances in order to run your CI workloads on amd64 and arm64 platforms respectively. Cirrus CI uses Kubernetes clusters running in different clouds that are the most suitable for running each platform:

  • For container instances Cirrus CI uses a GKE cluster of compute-optimized instances running in Google Cloud.
  • For arm_container instances Cirrus CI uses a EKS cluster of Graviton2 instances running in AWS.

Cirrus Cloud Clusters are configured the same way as anyone can configure a private Kubernetes cluster for their own repository. Cirrus CI supports connecting managed Kubernetes clusters from most of the cloud providers. Please check out all the supported computing services Cirrus CI can integrate with.

By default, a container is given 2 CPUs and 4 GB of memory, but it can be configured in .cirrus.yml:

container:
  image: openjdk:latest
  cpu: 4
  memory: 12G

task:
  script: ...

arm_container:
  image: openjdk:latest
  cpu: 4
  memory: 12G

task:
  script: ...

Containers on Cirrus Cloud Cluster can use maximum 8.0 CPUs and up to 32 GB of memory. Memory limit is tied to the amount of CPUs requested. For each CPU you can't get more than 4G of memory.

Tasks using Compute Credits has higher limits and can use up to 28.0 CPUs and 112G of memory respectively.

Using in-memory disks

Some I/O intensive tasks may benefit from using a tmpfs disk mounted as a working directory. Set use_in_memory_disk flag to enable in-memory disk for a container:

task:
  name: Much I/O
  container:
    image: alpine:latest
    use_in_memory_disk: true

task:
  name: Much I/O
  arm_container:
    image: alpine:latest
    use_in_memory_disk: true

Note: any files you write including cloned repository will count against your task's memory limit.

Privileged Access

If you need to run privileged docker containers, take a look at the docker builder.

Greedy instances

Greedy instances can potentially use more CPU resources if available. Please check this blog post for more details.

KVM-enabled Privileged Containers

It is possible to run containers with KVM enabled. Some types of CI tasks can tremendously benefit from native virtualization. For example, Android related tasks can benefit from running hardware accelerated emulators instead of software emulated ARM emulators.

In order to enable KVM module for your containers, add kvm: true to your container declaration. Here is an example of a task that runs hardware accelerated Android emulators:

task:
  name: Integration Tests (x86)
  container:
    image: cirrusci/android-sdk:30
    kvm: true
  accel_check_script: emulator -accel-check

Limitations of KVM-enabled Containers

Because of the additional virtualization layer, it takes about a minute to acquire the necessary resources to start such tasks. KVM-enabled containers are backed by dedicated VMs which restrict the amount of CPU resources that can be used. The value of cpu must be 1 or an even integer. Values like 0.5 or 3 are not supported for KVM-enabled containers

Working with Private Registries

It is possible to use private Docker registries with Cirrus CI to pull containers. To provide an access to a private registry of your choice you'll need to obtain a JSON Docker config file for your registry and create an encrypted variable for Cirrus CI to use.

Using Kubernetes secrets with private clusters

Alternatively, if you are using Cirrus CI with your private Kubernetes cluster you can create a kubernetes.io/dockerconfigjson secret and just use it's name for registry_config:

task:
  gke_container:
    image: secret:image
    registry_config: myregistrykey

Let's check an example of setting up Oracle Container Registry in order to use Oracle Database in tests.

First, you'll need to login with the registry by running the following command:

docker login container-registry.oracle.com

After a successful login, Docker config file located in ~/.docker/config.json will look something like this:

{
  "auths": {
    "container-registry.oracle.com": {
      "auth": "...."
    }
  }
}

If you don't see auth for your registry, it means your Docker installation is using a credentials store. In this case you can manually auth using a Base64 encoded string of your username and your PAT (Personal Access Token). Here's how to generate that:

echo $USERNAME:$PAT | base64

Create an encrypted variable from the Docker config and put in .cirrus.yml:

registry_config: ENCRYPTED[...]

Now Cirrus CI will be able to pull images from Oracle Container Registry:

registry_config: ENCRYPTED[...]

test_task:
  container:
    image: bigtruedata/sbt:latest
    additional_containers:
      - name: oracle
        image: container-registry.oracle.com/database/standard:latest
        port: 1521
        cpu: 1
        memory: 8G
   build_script: ./build/build.sh