Book Image

Learn Docker - Fundamentals of Docker 18.x

By : Dr. Gabriel N. Schenker
Book Image

Learn Docker - Fundamentals of Docker 18.x

By: Dr. Gabriel N. Schenker

Overview of this book

Docker containers have revolutionized the software supply chain in small and big enterprises. Never before has a new technology so rapidly penetrated the top 500 enterprises worldwide. Companies that embrace containers and containerize their traditional mission-critical applications have reported savings of at least 50% in total maintenance cost and a reduction of 90% (or more) of the time required to deploy new versions of those applications. Furthermore they are benefitting from increased security just by using containers as opposed to running applications outside containers. This book starts from scratch, introducing you to Docker fundamentals and setting up an environment to work with it. Then we delve into concepts such as Docker containers, Docker images, Docker Compose, and so on. We will also cover the concepts of deployment, orchestration, networking, and security. Furthermore, we explain Docker functionalities on public clouds such as AWS. By the end of this book, you will have hands-on experience working with Docker containers and orchestrators such as SwarmKit and Kubernetes.
Table of Contents (21 chapters)
Title Page
Packt Upsell
Contributors
Preface
Index

Kubernetes ReplicaSet


A single pod in an environment with high availability requirements is insufficient. What if the pod crashes?What if we need to update the application running inside the pod but cannot afford any service interruption? These questions and more can only indicate that pods alone are not enough and we need a higher-level concept that can manage multiple instances of the same pod. In Kubernetes, the ReplicaSet is used to define and manage such a collection of identical pods that are running on different cluster nodes. Among other things, a ReplicaSet defines which container images are used by the containers running inside a pod and how many instances of the pod will run in the cluster. These properties and the many others are called the desired state. 

The ReplicaSet is responsible for reconciling the desired state at all times, if the actual state ever deviates from it. Here is a Kubernetes ReplicaSet:

Kubernetes ReplicaSet

In the preceding diagram, we see such a ReplicaSet...