Leaked Kubernetes resources when a service-name / service-hostname changes

[mthaddon]

The nginx-ingress-integrator charm creates Kubernetes resources (Services and Ingress Resources) based on the configured service-name and service-hostname.

However, if the charm is then configured with a different service-name and service-hostname, the previous resources are not removed. This happens everytime the configuration options change since the Resource names are based on the aforementioned service-name / service-hostname.

This can also happen for the service-names and service-hostnames received from relation data (+ additional-hostnames for Ingress Resources). This issue occurs on previous revisions as well.

Because the Kubernetes resource names are based on service-name / service-hostname, cleaning them up is not immediately straight-forward since the charm would have to store the previous values and compare them to the current ones.

[weiiwang01]

Juju adds this label app.juju.is/created-by=<app-name> to all the k8s resources that ingress integrator charm created. That label can be used to select and remove unused resources.

$ microk8s kubectl describe service -n test-relation-0r1c any-service
Name:              any-service
Namespace:         test-relation-0r1c
Labels:            app.juju.is/created-by=ingress
Annotations:       <none>
Selector:          app.kubernetes.io/name=any
Type:              ClusterIP
IP Family Policy:  SingleStack
IP Families:       IPv4
IP:                10.152.183.176
IPs:               10.152.183.176
Port:              tcp-18080  18080/TCP
TargetPort:        18080/TCP
Endpoints:         10.1.75.154:18080
Port:              tcp-8080  8080/TCP
TargetPort:        8080/TCP
Endpoints:         10.1.75.154:8080
Session Affinity:  None
Events:            <none>

[mthaddon]

As long as we're looking for the entire app.juju.is/created-by=$app-name string this should be fine, but note that you may have multiple ingress applications deployed in a single model and we'd need to be careful to make sure we don't remove ingresses defined by an application named ingress-extra-cool application if we're deployed as an application named ingress.