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Concepts - Understanding Operators | Operators | OpenShift Container Platform 4.5
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Operator Lifecycle Manager concepts

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

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 OpenShift Container Platform 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 OpenShift Container Platform 4.5, which aids cluster administrators in installing, upgrading, and granting access to Operators running on their cluster. The OpenShift Container Platform 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.

Cluster service version

A cluster service version (CSV) represents a specific version of a running Operator on an OpenShift Container Platform 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 that OLM can query to discover and install Operators and their dependencies. 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.

There are three primary sourceTypes for a CatalogSource object:

  • 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.

  • internal or configmap: OLM parses the configmap data and runs a pod that can serve the gRPC API over it.

The following example defines a catalog source for OperatorHub.io content:

Example CatalogSource object
apiVersion: operators.coreos.com/v1alpha1
kind: CatalogSource
metadata:
 name: operatorhubio-catalog
 namespace: olm
spec:
 sourceType: grpc
 image: quay.io/operator-framework/upstream-community-operators:latest
 displayName: Community Operators
 publisher: OperatorHub.io

The name of the CatalogSource object is used as input to a subscription, which instructs OLM where to look to find a requested Operator:

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

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: my-operator
  namespace: operators
spec:
  channel: stable
  name: my-operator
  source: my-catalog
  sourceNamespace: operators

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 OpenShift Container Platform 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.

Install plan

An install plan, defined by an InstallPlan object, describes a set of resources to be created to install or upgrade to a specific version of an Operator, as defined by a cluster service version (CSV).

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.

For more information, see the Operator groups guide.