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

Defining volumes in images


If we go for a moment back to what we have learned about containers in Chapter 3Working with Containers, then we have this: the filesystem of each container when started is made up of the immutable layers of the underlying image plus a writable container layer specific to this very container. All changes that the processes running inside the container make to the filesystem will be persisted in this container layer. Once the container is stopped and removed from the system, the corresponding container layer is deleted from the system and irreversibly lost.

Some applications, such as databases running in containers, need to persist their data beyond the lifetime of the container. In this case they can use volumes. To make things a bit more explicit let's look at a concrete sample. MongoDB is a popular open source document database. Many developers use MongoDB as a storage service for their applications. The maintainers of MongoDB have created an image and published...