Architecture
Package Operator Manager
The main work of Package Operator is done by the Package Operator Manager. This
component is run as a deployment with a single replica. It contains the controllers
for (Cluster)Package, (Cluster)ObjectDeployment, and (Cluster)ObjectSet resources.
It also contains a controller for (Cluster)ObjectSetPhase objects. This controller
reconciles (Cluster)ObjectSetPhases with the .spec.class set to default.
Package Operator Manager also contains functionality to copy its own binary and load packages, which is discussed in the Loading Package Images Section, and functionality to allow Package Operator to bootstrap itself, which is discussed on the Installation Page.
Webhooks
There is a validation webhook server that can optionally be run with package operator.
This webhook server verifies the immutability of certain fields of ObjectSet
and ObjectSetPhase resources. If one of these immutable fields is changed in
an update, the webhook server will disallow the update.
Loading Package Images
A package is a single artifact that contains all manifests, configuration,
and metadata needed to run an application or operator. This single artifact takes
the form of a non-runnable container image. This image is supplied to Package
Operator in a (Cluster)Package object.
When Package Operator reconciles a (Cluster)Package object, it needs to access
the content of the package image. Package Operator does this by deploying a separate
Kubernetes Job. This Job has two containers, an init container called prepare-loader
and a regular container called package-loader.
The prepare-loader container uses the package-operator-manager image and copies
the package-operator-manager binary to a shared volume that both containers in
the Job have access to. We have to do this because as mentioned before, the package
image is non-runnable, so we have to assume it has no shell or copy utilities to
unpack the files it contains.
The package-loader container then uses the package-operator-manager binary to
create an ObjectDeployment that contains all the necessary information from the
package image. The Job then finishes and is garbage collected.