In Kubernetes, there is tight coupling of API group, CRD and Custom Resources managed by operators. CRDs are cluster resource and unique per cluster.
CRD operatorconfigurations.acid.zalan.do defines the operator configurations for postgres operator.
CRD postgresqls.acid.zalan.do defines minimum and maximum supported postgresql versions.
This leads to issues in a multi-tenant k8s cluster, an example provided below.
In Namespace X, user X deploys web tier application which uses zalando postgres-operator with max version PG 15.
In Namespace Y, user Y deploys web tier application which also uses zalando postgres-operator but needs PG 17 runs into an issue as CRD postgresqls.acid.zalan.do supports only PG 15. This happens because CRD is cluster scope and all namespace scoped applications should adhere to it.
With large k8s clusters, postgresql being a very popular database, zalando postgres operator being defacto way to manage databases, there is a need to keep this configurable so applications can manage the API group of CRDs.
Take API group for postgres operator as an env variable, assuming that the relevant CRDs with API groups are installed.
Client-go provides a https://github.com/kubernetes/code-generator package in order to provide the API to work with CRDs similar to the one available for built-in types, i.e. Pods, Statefulsets and so on.
Use this package to generate deepcopy methods (required for CRDs), instead of using an external deepcopy package; we also generate APIs used to manipulate both Postgres and OperatorConfiguration CRDs, as well as informers and listers for the Postgres CRD, instead of using generic informers and CRD REST API; by using generated code we can get rid of some custom and obscure CRD-related code and use a better API.
All generated code resides in /pkg/generated, with an exception of zz_deepcopy.go in apis/acid.zalan.do/v1
Rename postgres-operator-configuration CRD to OperatorConfiguration, since the former broke naming convention in the code-generator.
Moved Postgresql, PostgresqlList, OperatorConfiguration and OperatorConfigurationList and other types used by them into
Change the type of the Error field in the Postgresql crd to a string, so that client-go could generate a deepcopy for it.
Use generated code to set status of CRD objects as well. Right now this is done with patch, however, Kubernetes 1.11 introduces the /status subresources, allowing us to set the status with
the special updateStatus call in the future. For now, we keep the code that is compatible with earlier versions of Kubernetes.
Rename postgresql.go to database.go and status.go to logs_and_api.go to reflect the purpose of each of those files.
Update client-go dependencies.
Minor reformatting and renaming.
Nandan
Oleksii Kliukin