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Concepts and resources - Understanding Operators | Operators | OKD 4.7
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Operator Lifecycle Manager concepts and resources

This guide provides an overview of the concepts that drive Operator Lifecycle Manager (OLM) in OKD.

What is Operator Lifecycle Manager?

Operator Lifecycle Manager (OLM) helps users install, update, and manage the lifecycle of Kubernetes native applications (Operators) and their associated services running across their OKD clusters. It is part of the Operator Framework, an open source toolkit designed to manage Operators in an effective, automated, and scalable way.

olm workflow
Figure 1. Operator Lifecycle Manager workflow

OLM runs by default in OKD 4.7, which aids cluster administrators in installing, upgrading, and granting access to Operators running on their cluster. The OKD web console provides management screens for cluster administrators to install Operators, as well as grant specific projects access to use the catalog of Operators available on the cluster.

For developers, a self-service experience allows provisioning and configuring instances of databases, monitoring, and big data services without having to be subject matter experts, because the Operator has that knowledge baked into it.

OLM resources

The following custom resource definitions (CRDs) are defined and managed by Operator Lifecycle Manager (OLM):

Table 1. CRDs managed by OLM and Catalog Operators
Resource Short name Description

ClusterServiceVersion (CSV)

csv

Application metadata. For example: name, version, icon, required resources.

CatalogSource

catsrc

A repository of CSVs, CRDs, and packages that define an application.

Subscription

sub

Keeps CSVs up to date by tracking a channel in a package.

InstallPlan

ip

Calculated list of resources to be created to automatically install or upgrade a CSV.

OperatorGroup

og

Configures all Operators deployed in the same namespace as the OperatorGroup object to watch for their custom resource (CR) in a list of namespaces or cluster-wide.

OperatorConditions

-

Creates a communication channel between OLM and an Operator it manages. Operators can write to the Status.Conditions array to communicate complex states to OLM.

Cluster service version

A cluster service version (CSV) represents a specific version of a running Operator on an OKD cluster. It is a YAML manifest created from Operator metadata that assists Operator Lifecycle Manager (OLM) in running the Operator in the cluster.

OLM requires this metadata about an Operator to ensure that it can be kept running safely on a cluster, and to provide information about how updates should be applied as new versions of the Operator are published. This is similar to packaging software for a traditional operating system; think of the packaging step for OLM as the stage at which you make your rpm, deb, or apk bundle.

A CSV includes the metadata that accompanies an Operator container image, used to populate user interfaces with information such as its name, version, description, labels, repository link, and logo.

A CSV is also a source of technical information required to run the Operator, such as which custom resources (CRs) it manages or depends on, RBAC rules, cluster requirements, and install strategies. This information tells OLM how to create required resources and set up the Operator as a deployment.

Catalog source

A catalog source represents a store of metadata, typically by referencing an index image stored in a container registry. Operator Lifecycle Manager (OLM) queries catalog sources to discover and install Operators and their dependencies. The OperatorHub in the OKD web console also displays the Operators provided by catalog sources.

Cluster administrators can view the full list of Operators provided by an enabled catalog source on a cluster by using the Administration → Cluster Settings → Global Configuration → OperatorHub page in the web console.

The spec of a CatalogSource object indicates how to construct a pod or how to communicate with a service that serves the Operator Registry gRPC API.

Example CatalogSource object 
apiVersion: operators.coreos.com/v1alpha1
kind: CatalogSource
metadata:
  generation: 1
  name: example-catalog (1)
  namespace: olm (2)
spec:
  displayName: Example Catalog (3)
  image: quay.io/example-org/example-catalog:v1 (4)
  priority: -400 (5)
  publisher: Example Org
  sourceType: grpc (6)
  updateStrategy:
    registryPoll: (7)
      interval: 30m0s
status:
  connectionState:
    address: example-catalog.olm.svc:50051
    lastConnect: 2021-08-26T18:14:31Z
    lastObservedState: READY (8)
  latestImageRegistryPoll: 2021-08-26T18:46:25Z (9)
  registryService: (10)
    createdAt: 2021-08-26T16:16:37Z
    port: 50051
    protocol: grpc
    serviceName: example-catalog
    serviceNamespace: olm
1 Name for the CatalogSource object. This value is also used as part of the name for the related pod that is created in the requested namespace.
2 Namespace to create the catalog available. To make the catalog available cluster-wide in all namespaces, set this value to olm. The default Red Hat-provided catalog sources also use the olm namespace. Otherwise, set the value to a specific namespace to make the Operator only available in that namespace.
3 Display name for the catalog in the web console and CLI.
4 Index image for the catalog.
5 Weight for the catalog source. OLM uses the weight for prioritization during dependency resolution. A higher weight indicates the catalog is preferred over lower-weighted catalogs.
6 Source types include the following:

  • grpc with an image reference: OLM pulls the image and runs the pod, which is expected to serve a compliant API.

  • grpc with an address field: OLM attempts to contact the gRPC API at the given address. This should not be used in most cases.

  • configmap: OLM parses config map data and runs a pod that can serve the gRPC API over it.
7 Automatically check for new versions at a given interval to stay up-to-date.
8 Last observed state of the catalog connection. For example:

  • READY: A connection is successfully established.

  • CONNECTING: A connection is attempting to establish.

  • TRANSIENT_FAILURE: A temporary problem has occurred while attempting to establish a connection, such as a timeout. The state will eventually switch back to CONNECTING and try again.

See States of Connectivity in the gRPC documentation for more details.
9 Latest time the container registry storing the catalog image was polled to ensure the image is up-to-date.
10 Status information for the catalog’s Operator Registry service.

Referencing the name of a CatalogSource object in a subscription instructs OLM where to search to find a requested Operator:

Example Subscription object referencing a catalog source 
apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
  name: example-operator
  namespace: example-namespace
spec:
  channel: stable
  name: example-operator
  source: example-catalog
  sourceNamespace: olm
Additional resources

Subscription

A subscription, defined by a Subscription object, represents an intention to install an Operator. It is the custom resource that relates an Operator to a catalog source.

Subscriptions describe which channel of an Operator package to subscribe to, and whether to perform updates automatically or manually. If set to automatic, the subscription ensures Operator Lifecycle Manager (OLM) manages and upgrades the Operator to ensure that the latest version is always running in the cluster.

Example Subscription object
apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
  name: example-operator
  namespace: example-namespace
spec:
  channel: stable
  name: example-operator
  source: example-catalog
  sourceNamespace: olm

This Subscription object defines the name and namespace of the Operator, as well as the catalog from which the Operator data can be found. The channel, such as alpha, beta, or stable, helps determine which Operator stream should be installed from the catalog source.

The names of channels in a subscription can differ between Operators, but the naming scheme should follow a common convention within a given Operator. For example, channel names might follow a minor release update stream for the application provided by the Operator (1.2, 1.3) or a release frequency (stable, fast).

In addition to being easily visible from the OKD web console, it is possible to identify when there is a newer version of an Operator available by inspecting the status of the related subscription. The value associated with the currentCSV field is the newest version that is known to OLM, and installedCSV is the version that is installed on the cluster.

Additional resources

Install plan

An install plan, defined by an InstallPlan object, describes a set of resources that Operator Lifecycle Manager (OLM) creates to install or upgrade to a specific version of an Operator. The version is defined by a cluster service version (CSV).

To install an Operator, a cluster administrator, or a user who has been granted Operator installation permissions, must first create a Subscription object. A subscription represents the intent to subscribe to a stream of available versions of an Operator from a catalog source. The subscription then creates an InstallPlan object to facilitate the installation of the resources for the Operator.

The install plan must then be approved according to one of the following approval strategies:

  • If the subscription’s spec.installPlanApproval field is set to Automatic, the install plan is approved automatically.

  • If the subscription’s spec.installPlanApproval field is set to Manual, the install plan must be manually approved by a cluster administrator or user with proper permissions.

After the install plan is approved, OLM creates the specified resources and installs the Operator in the namespace that is specified by the subscription.

Example InstallPlan object 
apiVersion: operators.coreos.com/v1alpha1
kind: InstallPlan
metadata:
  name: install-abcde
  namespace: operators
spec:
  approval: Automatic
  approved: true
  clusterServiceVersionNames:
    - my-operator.v1.0.1
  generation: 1
status:
  ...
  catalogSources: []
  conditions:
    - lastTransitionTime: '2021-01-01T20:17:27Z'
      lastUpdateTime: '2021-01-01T20:17:27Z'
      status: 'True'
      type: Installed
  phase: Complete
  plan:
    - resolving: my-operator.v1.0.1
      resource:
        group: operators.coreos.com
        kind: ClusterServiceVersion
        manifest: >-
        ...
        name: my-operator.v1.0.1
        sourceName: redhat-operators
        sourceNamespace: openshift-marketplace
        version: v1alpha1
      status: Created
    - resolving: my-operator.v1.0.1
      resource:
        group: apiextensions.k8s.io
        kind: CustomResourceDefinition
        manifest: >-
        ...
        name: webservers.web.servers.org
        sourceName: redhat-operators
        sourceNamespace: openshift-marketplace
        version: v1beta1
      status: Created
    - resolving: my-operator.v1.0.1
      resource:
        group: ''
        kind: ServiceAccount
        manifest: >-
        ...
        name: my-operator
        sourceName: redhat-operators
        sourceNamespace: openshift-marketplace
        version: v1
      status: Created
    - resolving: my-operator.v1.0.1
      resource:
        group: rbac.authorization.k8s.io
        kind: Role
        manifest: >-
        ...
        name: my-operator.v1.0.1-my-operator-6d7cbc6f57
        sourceName: redhat-operators
        sourceNamespace: openshift-marketplace
        version: v1
      status: Created
    - resolving: my-operator.v1.0.1
      resource:
        group: rbac.authorization.k8s.io
        kind: RoleBinding
        manifest: >-
        ...
        name: my-operator.v1.0.1-my-operator-6d7cbc6f57
        sourceName: redhat-operators
        sourceNamespace: openshift-marketplace
        version: v1
      status: Created
      ...
Additional resources

Operator groups

An Operator group, defined by the OperatorGroup resource, provides multitenant configuration to OLM-installed Operators. An Operator group selects target namespaces in which to generate required RBAC access for its member Operators.

The set of target namespaces is provided by a comma-delimited string stored in the olm.targetNamespaces annotation of a cluster service version (CSV). This annotation is applied to the CSV instances of member Operators and is projected into their deployments.

Additional resources

Operator conditions

As part of its role in managing the lifecycle of an Operator, Operator Lifecycle Manager (OLM) infers the state of an Operator from the state of Kubernetes resources that define the Operator. While this approach provides some level of assurance that an Operator is in a given state, there are many instances where an Operator might need to communicate information to OLM that could not be inferred otherwise. This information can then be used by OLM to better manage the lifecycle of the Operator.

OLM provides a custom resource definition (CRD) called OperatorCondition that allows Operators to communicate conditions to OLM. There are a set of supported conditions that influence management of the Operator by OLM when present in the Status.Conditions array of an OperatorCondition resource.

Additional resources