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Understanding Docker Vocabulary

The purpose of Docker is to build containers that hold, potentially, all of the components of an application: the application itself, the database engine, any Web services it requires and so on. That container, unlike a virtual machine, doesn't require an operating system so it takes less space than a VM and starts up/shuts down faster.

The good news here is that there are a bunch of prepared containers waiting for you to use on Docker Hub: these are called images. Many of them are Linux based, but for .NET Core applications that's not an issue: Core runs as well on Linux as Windows. Docker Hub is an example of a Docker repository and, if you want, you can create your own repository for your company rather than use Docker Hub.

While you can put all the components of an application in a single container, you can also create individual containers for each component (one for the application, one for the database, one for each Web service). This allows you to upgrade/replace components individually or start multiple copies of one container to improve scalability. When you have multiple containers, you'll want to use Compose to create (and start) an application made up of multiple containers.

In production you'll want to be able to monitor your containers, auto-start the appropriate number of any of containers and automatically restart any container that fails. For that you need an orchestrator -- the elephant in this living room is Kubernetes ... which has its own vocabulary (Kubernetes works with services which are made up of pods, each of which may have one or more containers; servers with pods running on them are called nodes).

Most recently, you have Swarm which allows you to treat all the containers in a group as if it were one service.

It would, of course, help if you knew how all this stuff worked. But, with the right terms (and if you can keep the other person talking), you might be able to get through the interview.

Posted by Peter Vogel on 02/11/2019


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