Controller components

There are two main components of a controller: Informer/SharedInformer and Workqueue.Informer/SharedInformer watches for changes on the current state of Kubernetes objects and sends events to Workqueue where events are then popped up by worker(s) to process.

Informer

The vital role of a Kubernetes controller is to watch objects for the desired state and the actual state, then send instructions to make the actual state be more like the desired state.In order to retrieve an object’s information, the controller sends a request to Kubernetes API server.

However, repeatedly retrieving information from the API server can become expensive. Thus, in order to get and list objects multiple times in code, Kubernetes developers end up using cache which has already been provided by the client-go library. Additionally, the controller doesn’t really want to send requests continuously. It only cares about events when the object has been created, modified or deleted. The client-go library provides the Listwatcher interface that performs an initial list and starts a watch on a particular resource:

Anuj holds professional certifications in Google Cloud, AWS as well as certifications in Docker and App Performance Tools such as New Relic. He specializes in Cloud Security, Data Encryption and Container Technologies.

Initial Consultation

Anuj Varma – who has written posts on Anuj Varma, Hands-On Technology Architect, Clean Air Activist.

 Twitter Linkedin