Safely set annotation on datacenter

[akshaymankar]

What this PR does:

While setting any annotation, the user must initialize the Annotations
map if it isn't already. The helper metav1.SetMetadataAnnotation takes
care of this.

Which issue(s) this PR fixes:
N/A
The updateConfigHashAnnotation function panics when it encounters a datacenter without any annotations. This PR should fix that.

Checklist

• Changes manually tested
• Automated Tests added/updated
• Documentation added/updated
• CHANGELOG.md updated (not required for documentation PRs)
• CLA Signed: DataStax CLA

[burmanm]

Hi, thank you for the PR. Have you run into a situation where this actually occurs?

[akshaymankar]

Hi, thank you for the PR. Have you run into a situation where this actually occurs?

Yes, I have. The issue only occurs when using a separate kubernetes secret for the cassandra config overrides. The cass-operator gets stuck into a crash loop with this error at the end of the logs:

panic: assignment to entry in nil map

goroutine 328 [running]:
github.com/k8ssandra/cass-operator/pkg/reconciliation.(*ReconciliationContext).updateConfigHashAnnotation(0xc0008c4000, 0xc0008c52c0, 0x18a04b4, 0x6)
        /workspace/pkg/reconciliation/reconcile_configsecret.go:108 +0x1f3
github.com/k8ssandra/cass-operator/pkg/reconciliation.(*ReconciliationContext).CheckConfigSecret(0xc0008c4000, 0x1a95300, 0x2505678)
        /workspace/pkg/reconciliation/reconcile_configsecret.go:58 +0x5e6
github.com/k8ssandra/cass-operator/pkg/reconciliation.(*ReconciliationContext).ReconcileAllRacks(0xc0008c4000, 0x0, 0x0, 0x0, 0x0)
        /workspace/pkg/reconciliation/reconcile_racks.go:2435 +0x50b
github.com/k8ssandra/cass-operator/pkg/reconciliation.(*ReconciliationContext).CalculateReconciliationActions(0xc0008c4000, 0x0, 0x0, 0xc06f72bab7b14d8c, 0x45b80d114)
        /workspace/pkg/reconciliation/handler.go:160 +0x1b7
github.com/k8ssandra/cass-operator/controllers/cassandra.(*CassandraDatacenterReconciler).Reconcile(0xc000343e00, 0x1abb878, 0xc0007ea480, 0xc000253e34, 0x7, 0xc00013fd58, 0x15, 0xc0007ea400, 0x0, 0x0, ...)
        /workspace/controllers/cassandra/cassandradatacenter_controller.go:140 +0x8c7
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler(0xc000531a40, 0x1abb7d0, 0xc0004d9d00, 0x172dea0, 0xc000638140)
        /go/pkg/mod/sigs.k8s.io/controller-runtime@v0.9.2/pkg/internal/controller/controller.go:298 +0x30d
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem(0xc000531a40, 0x1abb7d0, 0xc0004d9d00, 0x4d82f00)
        /go/pkg/mod/sigs.k8s.io/controller-runtime@v0.9.2/pkg/internal/controller/controller.go:253 +0x205
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2(0xc0000495c0, 0xc000531a40, 0x1abb7d0, 0xc0004d9d00)
        /go/pkg/mod/sigs.k8s.io/controller-runtime@v0.9.2/pkg/internal/controller/controller.go:214 +0x6b
created by sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2
        /go/pkg/mod/sigs.k8s.io/controller-runtime@v0.9.2/pkg/internal/controller/controller.go:210 +0x425

A workaround for this is to set any annotation on the datacenter object.

[burmanm]

Apparently it's a bit different configuration than the one used in https://github.com/k8ssandra/cass-operator/blob/master/tests/config_secret/config_secret_suite_test.go ?

Do you think it would be possible to modify that integration test to also trigger this error? To ensure it's not unintentionally reintroduced (by botched mergeconflict for example).