kotovalexarian-likes-gitlab/gitlab-org--gitlab-foss

Achilleas Pipinellis 2343d3a5a4

2017-11-23 14:58:10 +01:00

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2017-11-10

Autoscaling GitLab Runner on AWS

One of the biggest advantages of GitLab Runner is its ability to automatically spin up and down VMs to make sure your builds get processed immediately. It's a great feature, and if used correctly, it can be extremely useful in situations where you don't use your Runners 24/7 and want to have a cost-effective and scalable solution.

Introduction

In this tutorial, we'll explore how to properly configure a GitLab Runner in AWS that will serve as the bastion where it will spawn new Docker machines on demand.

In addition, we'll make use of Amazon's EC2 Spot instances which will greatly reduce the costs of the Runner instances while still using quite powerful autoscaling machines.

Prerequisites

The first step is to install GitLab Runner in an EC2 instance that will serve as the bastion to spawning new machines. This doesn't have to be a powerful machine since it will not run any jobs itself, a t2.micro instance will do. This machine will be a dedicated host since we need it always up and running, thus it will be the only standard cost.

NOTE: Note: For the bastion instance, choose a distribution that both Docker and GitLab Runner support, for example either Ubuntu, Debian, CentOS or RHEL will work fine.

Install the prerequisites:

Log in your server
Install GitLab Runner from the official GitLab repository
Install Docker
Install Docker Machine

You can now move on to the most important part, configuring GitLab Runner.

Configuring GitLab Runner to use the AWS machine driver

Before configuring the GitLab Runner, you need to first register it, so that it connects with your GitLab instance.

Edit /etc/gitlab-runner/config.toml:

concurrent = 3
check_interval = 0

[[runners]]
  name = "gitlab-aws-autoscaler"
  url = "<url to your GitLab CI host>"
  token = "<registration token>"
  executor = "docker+machine"
  limit = 4
  [runners.docker]
    image = "alpine"
    privileged = true
    disable_cache = false
    volumes = ["/cache"]
  [runners.cache]
    Type = "s3"
    ServerAddress = "s3.amazonaws.com"
    AccessKey = "<your AWS Access Key ID>"
    SecretKey = "<your AWS Secret Access Key>"
    BucketName = "<the bucket where your cache should be kept>"
    BucketLocation = "us-east-1"
    Shared = true
  [runners.machine]
    IdleCount = 1
    IdleTime = 1800
    MaxBuilds = 100
    MachineDriver = "amazonec2"
    MachineName = "gitlab-docker-machine-%s"
    OffPeakPeriods = ["* * 0-7,19-23 * * mon-fri *", "* * * * * sat,sun *"]
    OffPeakIdleCount = 0
    OffPeakIdleTime = 1200
    MachineOptions = [
      "amazonec2-access-key=XXXX",
      "amazonec2-secret-key=XXXX",
      "amazonec2-region=us-east-1",
      "amazonec2-vpc-id=vpc-xxxxx",
      "amazonec2-subnet-id=subnet-xxxxx",
      "amazonec2-use-private-address=true",
      "amazonec2-tags=Name,gitlab-runner-autoscale",
      "amazonec2-security-group=docker-machine-scaler",
      "amazonec2-instance-type=m4.2xlarge",
      "amazonec2-ssh-user=ubuntu",
      "amazonec2-ssh-keypath=/etc/gitlab-runner/certs/gitlab-aws-autoscaler",
      "amazonec2-zone=a",
      "amazonec2-root-size=32",
    ]

Under MachineOptions you can add anything that the AWS Docker Machine driver supports.

Cutting down costs with Amazon EC2 Spot instances

As described by Amazon:

Amazon EC2 Spot instances allow you to bid on spare Amazon EC2 computing capacity. Since Spot instances are often available at a discount compared to On-Demand pricing, you can significantly reduce the cost of running your applications, grow your application’s compute capacity and throughput for the same budget, and enable new types of cloud computing applications.

In /etc/gitlab-runner/config.toml under the MachineOptions section:

    MachineOptions = [
      "amazonec2-request-spot-instance=true",
      "amazonec2-spot-price=0.03",
      "amazonec2-block-duration-minutes=60"
    ]

With this configuration, Docker Machines are created on Spot instances with a maximum bid price of $0.03 per hour and the duration of the Spot instance is capped at 60 minutes.

To learn more about Amazon EC2 Spot instances, visit the following links:

Caveats of Spot instances

If the Spot price raises, the auto-scale Runner would fail to create new machines.

This eventually eats 60 requests and then AWS won't accept any more. Then once the spot price is acceptable, you are locked out for a bit because the call amount limit is exceeded.

You can use the following command in the bastion machine to see the Docker Machines state:

docker-machine ls -q --filter state=Error --format "{{.NAME}}"

NOTE: Note: Follow issue 2771 for more information.

Conclusion

Using the autoscale feature of GitLab Runner can save you both time and money. Using the spot instances that AWS provides can save you even more.

You can read the following user cases from which this tutorial was influenced:

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