Book Image

The Kubernetes Operator Framework Book

By : Michael Dame
1 (1)
Book Image

The Kubernetes Operator Framework Book

1 (1)
By: Michael Dame

Overview of this book

From incomplete collections of knowledge and varying design approaches to technical knowledge barriers, Kubernetes users face various challenges when developing their own operators. Knowing how to write, deploy, and pack operators makes cluster management automation much easier – and that's what this book is here to teach you. Beginning with operators and Operator Framework fundamentals, the book delves into how the different components of Operator Framework (such as the Operator SDK, Operator Lifecycle Manager, and OperatorHub.io) are used to build operators. You’ll learn how to write a basic operator, interact with a Kubernetes cluster in code, and distribute that operator to users. As you advance, you’ll be able to develop a sample operator in the Go programming language using Operator SDK tools before running it locally with Operator Lifecycle Manager, and also learn how to package an operator bundle for distribution. The book covers best practices as well as sample applications and case studies based on real-world operators to help you implement the concepts you’ve learned. By the end of this Kubernetes book, you’ll be able to build and add application-specific operational logic to a Kubernetes cluster, making it easier to automate complex applications and augment the platform.
Table of Contents (16 chapters)
1
Part 1: Essentials of Operators and the Operator Framework
4
Part 2: Designing and Developing an Operator
9
Part 3: Deploying and Distributing Operators for Public Use

Designing a target reconciliation loop

Now that we have defined our Operator's UI by designing a CRD to represent it in the cluster and itemized the Operand resources that it will manage, we can move on to the core logic of the Operator. This logic is nestled within the main reconciliation loop.

As described in earlier chapters, Operators function on the premise of reconciling the current state of the cluster with the desired state set by users. They do this by periodically checking what that current state is. These checks are usually triggered by certain events that are related to the Operand. For example, an Operator will monitor the Pods in its target Operand namespace and react to the creation or deletion of a Pod. It is up to the Operator developers to define which events are of interest to the Operator.

Level- versus edge-based event triggering

When an event triggers the Operator's reconciliation loop, the logic does not receive the context of the whole event...