Labels and annotations

Resources in Kubernetes are organized in a flat structure, with no hierarchical information or relationship between them. However, such resources and objects can be linked together and put in relationship through labels and annotations.

Info

For more information, please refer to the Kubernetes documentation on annotations and labels.

In short:

an annotation is used to assign additional non-identifying information to resources with the goal to facilitate integration with external tools
a label is used to group objects and query them through Kubernetes' native selector capability

You can select one or more labels and/or annotations you will use in your CloudNativePG deployments. Then you need to configure the operator so that when you define these labels and/or annotations in a cluster's metadata, they are automatically inherited by all resources created by it (including pods).

Note

Label and annotation inheritance is the technique adopted by CloudNativePG in lieu of alternative approaches such as pod templates.

Predefined labels

Below is a list of predefined labels that are managed by CloudNativePG.

cnpg.io/backupName: Backup identifier, only available on Backup and VolumeSnapshot resources
cnpg.io/cluster: Name of the cluster
cnpg.io/immediateBackup: Applied to a Backup resource if the backup is the first one created from a ScheduledBackup object having immediate set to true.
cnpg.io/instanceName: Name of the PostgreSQL instance - this label replaces the old and deprecated postgresql label
cnpg.io/jobRole: Role of the job (i.e. import, initdb, join, ...)
cnpg.io/podRole: Currently fixed to instance to identify a pod running PostgreSQL
cnpg.io/poolerName: Name of the PgBouncer pooler
cnpg.io/pvcRole: Purpose of the PVC, such as PG_DATA or PG_WAL
cnpg.io/reload: Available on ConfigMap and Secret resources. When set to true, a change in the resource will be automatically reloaded by the operator.
cnpg.io/scheduled-backup: When available, name of the ScheduledBackup resource that created a given Backup object.
role: Whether the instance running in a pod is a primary or a replica

Predefined annotations

Below is a list of predefined annotations that are managed by CloudNativePG.

container.apparmor.security.beta.kubernetes.io/*: Name of the AppArmor profile to apply to the named container. See AppArmor documentation for details
cnpg.io/coredumpFilter: Filter to control the coredump of Postgres processes, expressed with a bitmask. By default it is set to 0x31 in order to exclude shared memory segments from the dump. Please refer to "PostgreSQL core dumps" for more information.
cnpg.io/clusterManifest: Manifest of the Cluster owning this resource (such as a PVC) - this label replaces the old and deprecated cnpg.io/hibernateClusterManifest label
cnpg.io/fencedInstances: List, expressed in JSON format, of the instances that need to be fenced. The whole cluster is fenced if the list contains the * element.
cnpg.io/forceLegacyBackup: Applied to a Cluster resource for testing purposes only, in order to simulate the behavior of barman-cloud-backup prior to version 3.4 (Jan 2023) when the --name option was not available.
cnpg.io/hash: The hash value of the resource
cnpg.io/hibernation: Applied to a Cluster resource to control the declarative hibernation feature. Allowed values are on and off.
cnpg.io/managedSecrets: Pull secrets managed by the operator and automatically set in the ServiceAccount resources for each Postgres cluster
cnpg.io/nodeSerial: On a pod resource, identifies the serial number of the instance within the Postgres cluster
cnpg.io/operatorVersion: Version of the operator
cnpg.io/pgControldata: Output of the pg_controldata command - this annotation replaces the old and deprecated cnpg.io/hibernatePgControlData annotation
cnpg.io/podEnvHash: Deprecated as the cnpg.io/podSpec annotation now also contains the pod environment
cnpg.io/podSpec: Snapshot of the spec of the Pod generated by the operator - this annotation replaces the old and deprecated cnpg.io/podEnvHash annotation
cnpg.io/poolerSpecHash: Hash of the pooler resource
cnpg.io/pvcStatus: Current status of the pvc, one of initializing, ready, detached
cnpg.io/reconciliationLoop: When set to disabled on a Cluster, the operator prevents the reconciliation loop from running
cnpg.io/reloadedAt: Contains the latest cluster reload time, reload is triggered by user through plugin
cnpg.io/skipEmptyWalArchiveCheck: When set to true on a Cluster resource, the operator disables the check that ensures that the WAL archive is empty before writing data. Use at your own risk.
kubectl.kubernetes.io/restartedAt: When available, the time of last requested restart of a Postgres cluster

Pre-requisites

By default, no label or annotation defined in the cluster's metadata is inherited by the associated resources. In order to enable label/annotation inheritance, you need to follow the instructions provided in the "Operator configuration" section.

Below we will continue on that example and limit it to the following:

annotations: categories
labels: app, environment, and workload

Note

Feel free to select the names that most suit your context for both annotations and labels. Remember that you can also use wildcards in naming and adopt strategies like mycompany/* for all labels or annotations starting with mycompany/ to be inherited.

Defining cluster's metadata

When defining the cluster, before any resource is deployed, you can properly set the metadata as follows:

apiVersion: postgresql.cnpg.io/v1
kind: Cluster
metadata:
  name: cluster-example
  annotations:
    categories: database
  labels:
    environment: production
    workload: database
    app: sso
spec:
     # ... <snip>

Once the cluster is deployed, you can verify, for example, that the labels have been correctly set in the pods with:

kubectl get pods --show-labels

Current limitations

Currently, CloudNativePG does not automatically propagate labels or annotations deletions. Therefore, when an annotation or label is removed from a Cluster, which was previously propagated to the underlying pods, the operator will not automatically remove it on the associated resources.