Labels and annotations¶
Labels and annotations are used to attach additional metadata information to Kubernetes resources.
Labels and annotations are rather similar. The difference between them is that labels are used by Kubernetes to identify and select objects, while annotations are assigning additional non-identifying information to resources. Therefore, typical role of Annotations is facilitating integration with some external tools.
Setting labels and annotations in the Custom Resource¶
You can set labels and/or annotations as key/value string pairs in the Custom
Resource metadata section of the deploy/cr.yaml as follows:
apiVersion: pxc.percona.com/v1
kind: PerconaXtraDBCluster
metadata:
name: cluster1
annotations:
percona.com/issue-vault-token: "true"
labels:
...
Note
Setting percona.com/issue-vault-token: "true" annotation is just an
example, but this exact annotation has a special meaning. If you add this
annotation present and have HashiCorp Vault
installed (for example, it is used for data at rest encryption),
the Operator will not start a cluster but will be printing a
wait for token issuing log message in a loop until the annotation is
deleted (for example, this can be combined with a user’s automation
script making some Vault-related preparations).
The easiest way to check which labels are attached to a specific object with is
using the additional --show-labels option of the kubectl get command.
Checking the annotations is not much more difficult: it can be done as in the
following example:
$ kubectl get pod cluster1-pxc-0 -o jsonpath='{.metadata.annotations}'
Specifying labels and annotations ignored by the Operator¶
Sometimes various Kubernetes flavors can add their own annotations to the objects managed by the Operator.
The Operator keeps track of all changes to its objects and can remove annotations that appeared without its participation.
If there are no annotations or labels in the Custom Resource, the Operator does nothing if new label or annotation added to the object.
If there is an annotation or a label specified in the Custom Resource, the Operator starts to manage annotations and labels. In this case it removes unknown annotations and labels.
Still, it is possible to specify which annotations and labels should be
ignored by the Operator by listing them in the spec.ignoreAnnotations or
spec.ignoreLabels keys of the deploy/cr.yaml, as follows:
spec:
ignoreAnnotations:
- some.custom.cloud.annotation/smth
ignoreLabels:
- some.custom.cloud.label/smth
...
The Operator will ignore any Service annotation or label, key of which
starts with the mentioned above examples. For example, the following
annotations and labels will be ignored after applying the above cr.yaml
fragment:
annotations:
some.custom.cloud.annotation/smth: somethinghere
labels:
some.custom.cloud.label/smth: somethinghere