Chapter 2. Operators

The OLM Operator is responsible for deploying applications defined by CSV resources after the required resources specified in the CSV are present in the cluster.

The OLM Operator is not concerned with the creation of the required resources; users can choose to manually create these resources using the CLI, or users can choose to create these resources using the Catalog Operator. This separation of concern enables users incremental buy-in in terms of how much of the OLM framework they choose to leverage for their application.

While the OLM Operator is often configured to watch all namespaces, it can also be operated alongside other OLM Operators so long as they all manage separate namespaces.

The Catalog Operator is responsible for resolving and installing CSVs and the required resources they specify. It is also responsible for watching CatalogSources for updates to packages in channels and upgrading them (optionally automatically) to the latest available versions.

A user that wishes to track a package in a channel creates a Subscription resource configuring the desired package, channel, and the CatalogSource from which to pull updates. When updates are found, an appropriate InstallPlan is written into the namespace on behalf of the user.

Users can also create an InstallPlan resource directly, containing the names of the desired CSV and an approval strategy, and the Catalog Operator creates an execution plan for the creation of all of the required resources. After it is approved, the Catalog Operator creates all of the resources in an InstallPlan; this then independently satisfies the OLM Operator, which proceeds to install the CSVs.

The Catalog Registry stores CSVs and CRDs for creation in a cluster and stores metadata about packages and channels.

A package manifest is an entry in the Catalog Registry that associates a package identity with sets of CSVs. Within a package, channels point to a particular CSV. Because CSVs explicitly reference the CSV that they replace, a package manifest provides the Catalog Operator all of the information that is required to update a CSV to the latest version in a channel (stepping through each intermediate version).

An Operator is considered a member of an OperatorGroup if the following conditions are true:

An InstallMode consists of an InstallModeType field and a boolean Supported field. A CSV’s spec can contain a set of InstallModes of four distinct InstallModeTypes:

Specify the set of namespaces for the OperatorGroup using a label selector with the spec.selector field:

apiVersion: operators.coreos.com/v1
kind: OperatorGroup
metadata:
  name: my-group
  namespace: my-namespace
  spec:
    selector:
      matchLabels:
        cool.io/prod: "true"

You can also explicitly name the target namespaces using the spec.targetNamespaces field:

apiVersion: operators.coreos.com/v1
kind: OperatorGroup
metadata:
  name: my-group
  namespace: my-namespace
spec:
  targetNamespaces:
  - my-namespace
  - my-other-namespace
  - my-other-other-namespace

Alternatively, you can omit both spec.selector and spec.targetNamespaces to specify a global OperatorGroup, which selects all namespaces:

apiVersion: operators.coreos.com/v1
kind: OperatorGroup
metadata:
  name: my-group
  namespace: my-namespace

The resolved set of selected namespaces is shown in an OperatorGroup’s status.namespaces field. A global OperatorGroup’s status.namespace contains the empty string (""), which signals to a consuming Operator that it should watch all namespaces.

Member CSVs of an OperatorGroup have the following annotations:

Information about what GroupVersionKinds (GVKs) are provided by an OperatorGroup are shown in an olm.providedAPIs annotation. The annotation’s value is a string consisting of <kind>.<version>.<group> delimited with commas. The GVKs of CRDs and APIServices provided by all active member CSVs of an OperatorGroup are included.

Review the following example of an OperatorGroup with a single active member CSV that provides the PackageManifest resource:

apiVersion: operators.coreos.com/v1
kind: OperatorGroup
metadata:
  annotations:
    olm.providedAPIs: PackageManifest.v1alpha1.packages.apps.redhat.com
  name: olm-operators
  namespace: local
  ...
spec:
  selector: {}
  serviceAccount:
    metadata:
      creationTimestamp: null
  targetNamespaces:
  - local
status:
  lastUpdated: 2019-02-19T16:18:28Z
  namespaces:
  - local

When an OperatorGroup is created, three ClusterRoles are generated. Each contains a single AggregationRule with a ClusterRoleSelector set to match a label, as shown below:

The following RBAC resources are generated when a CSV becomes an active member of an OperatorGroup, as long as the CSV is watching all namespaces with the AllNamespaces InstallMode and is not in a failed state with reason InterOperatorGroupOwnerConflict.

OLM creates copies of all active member CSVs of an OperatorGroup in each of that OperatorGroup’s target namespaces. The purpose of a copied CSV is to tell users of a target namespace that a specific Operator is configured to watch resources created there. Copied CSVs have a status reason Copied and are updated to match the status of their source CSV. The olm.targetNamespaces annotation is stripped from copied CSVs before they are created on the cluster. Omitting the target namespace selection avoids the duplication of target namespaces between tenants. Copied CSVs are deleted when their source CSV no longer exists or the OperatorGroup that their source CSV belongs to no longer targets the copied CSV’s namespace.

An OperatorGroup is static if its spec.staticProvidedAPIs field is set to true. As a result, OLM does not modify the OperatorGroup’s olm.providedAPIs annotation, which means that it can be set in advance. This is useful when a user wants to use an OperatorGroup to prevent resource contention in a set of namespaces but does not have active member CSVs that provide the APIs for those resources.

Below is an example of an OperatorGroup that protects Prometheus resources in all namespaces with the something.cool.io/cluster-monitoring: "true" annotation:

apiVersion: operators.coreos.com/v1
kind: OperatorGroup
metadata:
  name: cluster-monitoring
  namespace: cluster-monitoring
  annotations:
    olm.providedAPIs: Alertmanager.v1.monitoring.coreos.com,Prometheus.v1.monitoring.coreos.com,PrometheusRule.v1.monitoring.coreos.com,ServiceMonitor.v1.monitoring.coreos.com
spec:
  staticProvidedAPIs: true
  selector:
    matchLabels:
      something.cool.io/cluster-monitoring: "true"

Two OperatorGroups are said to have intersecting provided APIs if the intersection of their target namespace sets is not an empty set and the intersection of their provided API sets, defined by olm.providedAPIs annotations, is not an empty set.

A potential issue is that OperatorGroups with intersecting provided APIs can compete for the same resources in the set of intersecting namespaces.

For each Operator, the OperatorSource is used to define the external data store used to store Operator bundles. A simple OperatorSource includes:

An Operator’s CatalogSourceConfig is used to enable an Operator present in the OperatorSource on the cluster.

A simple CatalogSourceConfig must identify:

This procedure uses the Couchbase Operator as an example to install and subscribe to an Operator from the OperatorHub using the OpenShift Container Platform web console.

Instead of using the OpenShift Container Platform web console, you can install an Operator from the OperatorHub using the CLI. Use the oc command to create or update a CatalogSourceConfig object, then add a Subscription object.