Conceptually, an Operator takes human operational knowledge and encodes it into software that is more easily packaged and shared with consumers. Think of an Operator as an extension of the software vendor’s engineering team that watches over a Kubernetes environment and uses its current state to make decisions in milliseconds. Advanced Operators are designed to handle upgrades seamlessly, react to failures automatically, and not take shortcuts, like skipping a software backup process to save time.
More technically, an Operator is a method of packaging, deploying and managing a Kubernetes application. A Kubernetes application is an application that is both deployed on Kubernetes and managed using the Kubernetes APIs and kubectl/oc tooling. You can think of Operators as the runtime that manages this type of application on Kubernetes.
A: These APIs are feature rich, have clients for all platforms and plug into the cluster’s access control/auditing. An Operator uses the Kubernetes’ extension mechanism so your custom object, eg “MongoDB”, looks and acts just like the built-in Kubernetes objects.
A: A Service Broker is a step towards programmatic discovery and deployment of an application but it has one flaw: it’s not a long running process, so it can’t execute any Day 2 operations like upgrade, failover, scale out, etc. This is the problem with technologies like Helm. Customizations and parameterization of tunables can only be provided at install time, versus an Operator that is constantly watching your cluster’s current state. Off-cluster services continue to be a good match for a Service Broker, although Operators exist for these as well.
A: Helm charts are a popular framework for templatizing of Kubernetes manifests. They are helpful in simplifying the deployment of applications that have multiple manifests, each with different parameter values depending on context/environment. As such, Helm is a complimentary framework to an Operator backed application. With a complementary approach, the Operator would leverage the Helm chart to deploy the application and the Operator code would provide the day-2 operations logic.