• Prepare the environment
• Configuration
• Example: 1 job per instance using AWS Autoscaling group

Docker Autoscaler executor (Experiment)

The Docker Autoscaler executor is an autoscale-enabled Docker executor that creates instances on-demand to accommodate the jobs that the runner manager processes.

The autoscaler uses fleeting plugins. fleeting is an abstraction for a group of autoscaled instances and uses plugins that support different cloud providers (such as GCP, AWS and Azure). This allows instances to be created on-demand to accommodate the jobs that the runner manager processes.

Prepare the environment

To prepare your environment for autoscaling, install the AWS fleeting plugin. The fleeting plugin targets the platform that you want to autoscale on.

The AWS fleeting plugin is an Experiment. You can find our other official plugins here.

To install the AWS plugin:

1. Download the binary for your host platform.
2. Ensure that the plugin binaries are discoverable through the PATH environment variable.

Configuration

The Docker Autoscaler executor wraps the Docker executor, which means that all Docker executor options and features are supported. To enable the autoscaler, define the executor as docker-autoscaler.

• Docker Executor configuration
• Autoscaler configuration

Example: 1 job per instance using AWS Autoscaling group

Prerequisites:

• An AMI with Docker Engine installed.
• An AWS Autoscaling group. For the scaling policy use “none”, as Runner handles the scaling.
• An IAM Policy with the correct permissions

This configuration supports:

• A capacity per instance of 1
• A use count of 1
• An idle scale of 5
• An idle time of 20 minutes
• A maximum instance count of 10

By setting the capacity and use count to both 1, each job is given a secure ephemeral instance that cannot be affected by other jobs. As soon the job is complete the instance it was executed on is immediately deleted.

With an idle scale of 5, the runner tries to keep 5 whole instances (because the capacity per instance is 1) available for future demand. These instances stay for at least 20 minutes.

The runner concurrent field is set to 10 (maximum number instances * capacity per instance).

concurrent = 10

[[runners]]
  name = "instance autoscaler example"
  url = "https://gitlab.com"
  token = "<token>"
  shell = "sh"                                        # use powershell or pwsh for Windows AMIs

  # uncomment for Windows AMIs when the Runner manager is hosted on Linux
  # environment = ["FF_USE_POWERSHELL_PATH_RESOLVER=1"]

  executor = "docker-autoscaler"

  # Docker Executor config
  [runners.docker]
    image = "busybox:latest"

  # Autoscaler config
  [runners.autoscaler]
    plugin = "fleeting-plugin-aws"

    capacity_per_instance = 1
    max_use_count = 1
    max_instances = 10

    [runners.autoscaler.plugin_config] # plugin specific configuration (see plugin documentation)
      name             = "my-docker-asg"               # AWS Autoscaling Group name
      profile          = "default"                     # optional, default is 'default'
      config_file      = "/home/user/.aws/config"      # optional, default is '~/.aws/config'
      credentials_file = "/home/user/.aws/credentials" # optional, default is '~/.aws/credentials'

    [runners.autoscaler.connector_config]
      username          = "ec2-user"
      use_external_addr = true

    [[runners.autoscaler.policy]]
      idle_count = 5
      idle_time = "20m0s"