buildkite-spot-fleet-scaler

What is this?

buildkite-spot-fleet-scaler is a script that scales fleet(s) of Buildkite agents up/down as necessary based on the number of queued jobs for each fleet.

Dependencies

The AWS CLI (aws) command
Data::Compare (libdata-compare-perl on Debian)
IPC::Run (libipc-run-perl on Debian)
JSON (libjson-perl on Debian)
List::Compare (liblist-compare-perl on Debian)
List::Util (included in Perl core)
LWP (included in Perl core)

The AWS user used for the script needs to have permissions like the following IAM policy:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": "ec2:ModifySpotFleetRequest",
            "Resource": "arn:aws:ec2:*:652694334613:spot-fleet-request/*",
            "Condition": {
                "ForAllValues:StringEquals": {
                    "ec2:ResourceTag/buildkite-scaler-enable": "1"
                }
            }
        },
        {
            "Sid": "VisualEditor1",
            "Effect": "Allow",
            "Action": [
                "ec2:DescribeTags",
                "ec2:DescribeSpotFleetRequests"
            ],
            "Resource": "*"
        }
    ]
}

An "API Token" must be created on Buildkite that has the "Read Builds" permission.

How to use it?

This script only handles scaling of existing Spot Fleet Requests, you have to create those yourself.

To enable automatic scaling add the following tags to your Spot Fleet Requests:

# 'meta-data' parameter from buildkite-agent.cfg
buildkite-agent-meta-data = "queue=default"

# 'spawn' parameter from buildkite-agent.cfg
buildkite-agent-spawn = "1"

# Minimum and maximum number of allowed spot instances.
buildkite-scaler-min-instances = "0"
buildkite-scaler-max-instances = "2"

# Enable the scaler on this fleet.
buildkite-scaler-enable = "1"

# Automatically terminate agents when there is no work (optional).
# NOTE: This is prone to race conditions. I suggest leaving this disabled and designing the agent
# AMIs so that they shut themselves down when idle instead.
buildkite-scaler-terminate-on-scale-down = "1"

Set BUILDKITE_ORGANIZATION and BUILDKITE_API_KEY in the environment and run the buildkite-spot-fleet-scaler script with no arguments. The script will update the fleet target capacities as necessary once and then exit. Run it from cron or another part of your automation pipeline.

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