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

Demystifying declarative versus imperative


Docker Compose is a tool provided by Docker that is mainly used where one needs to run and orchestrate containers running on a single Docker host. This includes but is not limited to development, continuous integration (CI), automated testing, and manual QA.

Docker Compose uses files formatted in YAML as input. By default, Docker Compose expects these files to be called docker-compose.yml, but other names are possible. The content of a docker-compose.yml is said to be a declarative way of describing and running a containerized application potentially consisting of more than a single container.

So, what is the meaning of declarative?

First of all, declarative is the antonym of imperative. Well, that doesn't help much. Now that I have introduced another definition, I need to explain both of them:

  • Imperative: It's a way in which we can solve problems by specifying the exact procedure which has to be followed by the system.

If I tell a system such as the...