Most applications these days do not run in isolation; they need to communicate with other systems over the network. If we want to run a website, web service, database, or a cache server inside a Docker container, we need to first understand how to run a service and expose its port to other applications.
Docker networking
Running services
Let's start with a simple example, and run a Tomcat server directly from Docker Hub:
$ docker run -d tomcat
Tomcat is a web application server whose user interface can be accessed by port 8080. Therefore, if we installed Tomcat on our machine, we could browse it at http://localhost:8080. In our case, however, Tomcat is running inside the Docker container.
We started it the same way we...
