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Docker in Action
Docker and the container community have come a long way since we started participating in 2013. And Docker has changed in some unexpected ways since 2016, when Jeff released the first edition of this book. Thankfully, most of the user-facing interfaces and core concepts were maintained in a backward-compatible manner. The first two-thirds of the book needed updates only for additional features or closed issues. As anticipated, part 3 of the previous edition needed a full rewrite. Since publication of the previous book, we’ve seen progress in orchestration, app connectivity, proprietary cloud container offerings, multicontainer app packaging, and function-as-a-service platforms. This edition focuses on the fundamental concepts and practices for using Docker containers and steers clear of rapidly changing technologies that complement Docker.
The biggest change is the development and adoption of several container orchestrators. The primary purpose of a container orchestrator is to run applications modeled as services across a cluster of hosts. Kubernetes, the most famous of these orchestrators, has seen significant adoption and gained support from every major technology vendor. The Cloud Native Computing Foundation was formed around that project, and if you ask them, a “cloud native” app is one designed for deployment on Kubernetes. But it is important not to get too caught up in the marketing or the specific orchestration technology. This book does not cover Kubernetes for two reasons.
While Kubernetes is included with Docker for Desktop, it is massive and in constant flux. It could never be covered at any depth in a handful of chapters or even in a book with fewer than 400 pages. A wealth of excellent resources are available online as well as wonderful published books on Kubernetes. We wanted to focus on the big idea—service orchestration—in this book without getting too lost in the nuances.
Second, Docker ships with Swarm clustering and orchestration included. That system is more than adequate for smaller clusters, or clusters in edge computing environments. A huge number of organizations are happily using Swarm every day. Swarm is great for people getting started with orchestration and containers at the same time. Most of the tooling and ideas carry over from containers to services with ease. Application developers will likely benefit the most from this approach. System administrators or cluster operations personnel might be disappointed, or might find that Swarm meets their needs. But, we’re not sure they’ll ever find a long-form written resource that will satisfy their needs.
The next biggest change is that Docker runs everywhere today. Docker for Desktop is well integrated for use on Apple and Microsoft operating systems. It hides the underlying virtual machine from users. For the most part, this is a success; on macOS, the experience is nearly seamless. On Windows, things seem to go well at least for a few moments. Windows users will deal with an intimidating number of configuration variations from corporate firewalls, aggressive antivirus configuration, shell preferences, and several layers of indirection. That variation makes delivering written content for Windows impossible. Any attempt to do so would age out before the material went to production. For that reason, we’ve again limited the included syntax and system-specific material to Linux and macOS. A reader just might find that all the examples actually run in their environment, but we can’t promise that they will or reasonably help guide troubleshooting efforts.
Next, getting an internet-attached virtual machine with Docker installed has become trivial. Every major and minor cloud provider offers as much. For that reason, we’ve removed material pertaining to Docker Machine and installing Docker. We’re confident that our readers will be able to find installation instructions that are most appropriate for the platform of their choice. And today, they might even skip that step and adopt one of the many container-first cloud platforms like AWS ECS. This book won’t cover those platforms. They’re each unique enough to be difficult to discuss in aggregate. And all of them have put significant effort into their adoption stories and documentation.
Finally, containers and networking have had a complicated history. In the last few years, that story became just a little bit more complicated with the emergence of service mesh platforms and other complementary technologies. A service mesh is a platform of application-aware smart pipes that provide microservice networking best practices out of the box. They use proxies to provide point-to-point encryption, authentication, authorization, circuit-breakers, and advanced request routing. The container networking fundamentals presented in this book should prove useful in understanding and evaluating service mesh technologies.
This book is intended as a deep introduction to the fundamentals of working with Docker. A reader might not learn everything that they need in their daily application of this technology. But they will have the fundamental skillset required to learn advanced topics more quickly and further those pursuits. We wish you the best of luck in those containerized ventures.