Architecture
Summary
Fundamentally, Aegir5 maps a web GUI to CLI commands. It is made up of several components:
- There is a front-end built on Drupal 8. This is the default Admin UI and authoritative Object Model for the sytem.
- There is a queue system based on a RabbitMQ/Celery task queue to dispatch tasks.
- There is a back-end which consumes queued tasks and uses the data to execute Operations by rendering templates and running commands.
- The Drupal REST API enables any number of alternate frontends to manipulate the Object Model and trigger Operations.
The front-end UI allows users to construct the Object Model, creating Projects, Applications and Deployments to represent the applications and instances they need to provision, host, and manage. Users can interact with Projects and Applications by running Operations, composed of Tasks, which pass configuration variables into a distributed task queue, built on Celery.
The back-end is intended to be pluggable, and we have the basics of an Ansible-based backend in place, as well as a standalone Kubernetes-based backend which we intend to incorporate.
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The queue system Celery worker (dispatcherd) receives these tasks, and
runs provisioner commands, based on the variables passed into the task from the
front-end. Currently the only backend provisioner is Ansible, but the system is
designed to support pluggable provisioners such as Terraform, Kubernetes, or
plain shell scripts.
In previous editions of Aegir, we sometimes saw the split-brain problem arise as a result of the Frontend and Backend sharing responsibility for the state of the system.
In Aegir5, the Frontend is intended to be canonical with regards to the data about the state of a running application. Aegir manages the Environment, consisting of the application state (files + database).
The Project incorporates the infrastructure Kubernetes resources required to host the application. Drumkit provides commands to initialize a project with such resource definitions.