Kubernetes is a portable, extensible, open-source platform for managing containerized workloads and services, that facilitates both declarative configuration and automation. It has a large, rapidly growing ecosystem. Kubernetes services, support, and tools are widely available.
An Operator extends Kubernetes to automate the management of the entire lifecycle of a particular application. Operators serve as a packaging mechanism for distributing applications on Kubernetes, and they monitor, maintain, recover, and upgrade the software they deploy.
Operator - the custom controller installed on a Kubernetes cluster, in our case Hazelcast Jet Operator.
Operand - the managed workload provided by the Operator as a service, in our case Hazelcast Jet cluster.
Custom Resource (CR) - an instance of the
the Operator ships that represents the Operand or an Operation on an
Operand (also known as primary resources)
Managed resources - the Kubernetes objects or off-cluster services the Operator uses to constitute an Operand (also known as secondary resources)
Custom Resource Definition (CRD) - an API of the Operator, providing the blueprint and validation rules for Custom Resources.
SDK for building Kubernetes applications. Provides high level APIs, useful abstractions, and project scaffolding.
The SDK provides workflows to develop operators in Go, Ansible, or Helm.
Since we've already had Helm packages for Hazelcast Jet and Hazelcast Jet Enterprise, it makes sense to create first version of the operator based on Helm.
Operator SDK provides a CLI tool to generate Operators from Helm charts, however it is not sufficient to use to generated Operator as is, some tweaks are needed to fine tune its permissions.
Operator Capability Levels
Operators come in different maturity levels in regards to their lifecycle management capabilities for the application or workload they deliver. The capability models aims to provide guidance in terminology to express what features users can expect from an operator.
Hazelcast Jet Helm based operators currently categorized as Level 1 operator.
Operator Lifecycle Manager (OLM)
OLM extends Kubernetes to provide a declarative way to install, manage, and upgrade Operators and their dependencies in a cluster.
OLM defines a schema for Operator metadata, called the Cluster Service Version (CSV), for describing an Operator and its dependencies.
Operators with a CSV can be listed as entries in a catalog (i.e OperatorHub.io) available to OLM running on a Kubernetes cluster. Users then subscribe to an Operator from the catalog to tell OLM to provision and manage a desired Operator. That Operator, in turn, provisions and manages its application or service on the cluster.
Operator SDK CLI tool provides capability to generate CSVs but it's far from catalog listing criteria so manual curation of CSVs needed in our case. After creating the initial version of the CSV, making updates to it is pretty straightforward.
High Level Overview
The image above shows interactions between and user after the Hazelcast
Jet Operator has been deployed to the cluster. User submits the custom
resource with the type of
HazelcastJet and Hazelcast Jet Operator
handles the request.
Based on the contents of the requests Operator either instantiates a new cluster or reconciles the existing ones with the desired state.
RedHat Certified Operators
RedHat has a certification programme for Operators and certified Operators will get published to the OpenShift catalog. The criteria for certification can be found here
We've passed through this process for Hazelcast Jet Enterprise Operator and it can be installed directly from the OpenShift catalog from the UI.
During the process we've created OpenShift specific docker images for Hazelcast Jet Enterprise and Hazelcast Jet Management Center . Those images are built and published using RedHat Partner Connect build service. Released versions of those images can be found in the RedHat Container Catalog for Hazelcast Jet Enterprise and Hazelcast Jet Management Center.
Smoke testing has been done on our OpenShift on-premise test lab for the certified operator.
For community/non-certified versions of the operators which gets published to the OperatorHub.io are tested automatically with a corresponding Jenkins pipeline which deploys them to a regular Kubernetes cluster and verifies the cluster formation.
Automated test pipeline, which creates a Hazelcast Jet cluster with Management Center using OpenShift specific images then verifies its health, has been added to the Jenkins.
It is logical to extend capabilities of the operators to cover more scenarios rather than the basic installation.