Named after Joule expansion, Joule helps you to automate the scaling of applications inside cloud scale groups.
Install with snap install joule-expansion --classic.
Set these with snap set joule-expansion ${option}=${value}. The snap will
remain in blocked state until these are set.
provider: name of provider. E.g. "aws".applications: comma separated list of application names. E.g. "microk8s".
debug: set to anything except an empty string to enable debug log level.
Joule is split into 2 parts; the provider and the application. The provider's main loop consumes an application in order to operate it.
A provider object defines how Joule communicates with the cloud provider. It listens to a scale group's event queue in order to prepare the application for scale in and scale out events.
An application object defines how Joule drives the application you're running at scale by responding to events from the provider.
There are 3 events that are abstracted from the provider into the application.
Created after a new instance has started and is only handled on the new instance. Use this for any configuration that needs to be done to the application to join the cluster. For example, passing a token to the application in order to authenticate it into the cluster.
Created on an existing instance when a new instance has been launched by the provider. Use this for handling any actions required before the new instance are joined to the cluster. It could be run on any existing instance in the cluster. For example, adding the new instance to a list of allowed hosts.
Created on a remaining instance when an instance is terminated. Use this to cleanup anything within the cluster after termination of an instance. It could be run on any remaining instance on the cluster. For example, removing the instance from a list of allowed hosts.