Multipass Target Plugin (for Nomad Autoscaler)

This repo contains a plugin for the Nomad Autoscaler, which enables cluster scaling policies to target Multipass VMs.

Prerequisites

The intended use-case for this plugin is you:

• having installed Multipass on your local workstation and
• having deployed a set of Multipass VMs to host a Nomad cluster,
• need the capability to auto-scale the Nomad client VMs in your cluster.

This document will not cover Multipass installation, as it is better handled in the official docs.

If the Nomad Autoscaler is run within a Multipass VM (as opposed to running on the Multipass host), the Multipass daemon must be configured to accept remote communication, which requires that the local.passphrase configuration key has been set.

An example of deploying a Nomad cluster on Multipass VMs can be found here.

Installation

Presuming that the Autoscaler will be run as a Nomad job, this plugin can be installed using an artifact block in the job spec:

locals {
  # eg. https://github.com/michaelmosher/nomad-plugin-multipass-target/releases/download/v1/nomad-plugin-multipass-target-linux-amd64
  plugin_repo     = "https://github.com/michaelmosher/nomad-plugin-multipass-target"
  plugin_version  = "v13"
  plugin_artifact = "multipass-target-${attr.kernel.name}-${attr.cpu.arch}.zip"
  plugin_artifact_url = format("%s/releases/download/%s/%s",
    local.plugin_repo, local.plugin_version, local.plugin_artifact,
  )
}

job "nomad-auto-scaler" {
  ...
  group "agent" {
    ...
    task "main" {
      ...
      artifact {
        source      = local.plugin_artifact_url
        destination = "local/plugins"
      }
    }
  }
}

Plugin Configuration

When configuring the plugin itself (ie. in the target block of the auto-scaler config file), the following attributes must be provided:

Name	Description
multipass_address	The network address for the Multipass daemon. If the Autoscaler is run on the Multipass host, this can instead be the path to a Unix socket (eg. unix:///var/run/multipass_socket).
client_cert_path	The path to the PEM-encoded public certificate of an X.509 certificate which the plugin can use when opening a TLS connection to the Multipass daemon.
client_key_path	The path to the PEM-encoded private key of an X.509 certificate which the plugin can use when opening a TLS connection to the Multipass daemon.
passphrase	The value of local.passphrase for the Multipass daemon, as configured above.

Scaling Target Configuration

When configuring a Multipass scaling target (ie. in the target block of a cluster scaling policy), the following attributes must be provided:

Name	Description
cloud_init_user_data_path	The path to a Cloud-init user-data file to use when launching new Multipass VMs.
instance_image_name	The name of the image to use when launching new Multipass VMs (ie. as shown by multipass find).
node_class	The node_class of the auto-scaled Nomad clients. This is also used as a name prefix when launching new Multipass VMs.

Note: for auto-scaling to work properly, it is essential that the user-data provided configures the Nomad client as a member of the node_class provided.