[Request] Configuration to grab env vars/system properties and include in registration target node labels/annotations

[andrewazores]

cryostatio/cryostat#635 (comment)

Following on from that discussion, it would be useful for users to be able to configure the Agent to include various things into the node labels and annotations on the Target node that the Agent publishes to the Cryostat server representing itself. These could be specified as MicroProfile Config properties as generic Maps (one for labels and one for annotations). At deployment time, the user can choose to set the values as hardcoded values or to set them by referencing other environment variables. This way, the user can do things like capture Kubernetes Downward API values and embed these into node labels/annotations.

[andrewazores]

Related to #381

[andrewazores]

https://kubernetes.io/docs/concepts/workloads/pods/downward-api/#downwardapi-fieldRef

For reference. Also, putting the Pod's labels/annotations into a mounted volume at a well-known path is another potentially useful avenue here. The Operator could include this in the Agent autoconfiguration feature so that the k8s Pod labels/annotations are automatically mounted to the application, and the Agent can know where to look to find those, then include them in the self-describing discovery node. Then, any labels/annotations that the user applies to their application (ex. via Deployment .spec.template.metadata) would be automatically included in the Agent's discovery node.

[andrewazores]

The Operator can also put the Pod name and namespace into env. vars. via the Downward API and the Agent can pick up those details automatically for use in the discovery publication.