Beyond the Twelve-Factor App

Chapter 11. Port Binding

Factor 7 states that cloud-native applications export services via port binding.

Avoiding Container-Determined Ports

Web applications, especially those already running within an enterprise, are often executed within some kind of server container. The Java world is full of containers like Tomcat, JBoss, Liberty, and WebSphere. Other web applications might run inside other containers, like Microsoft Internet Information Server (IIS).

In a noncloud environment, web applications are deployed to these containers, and the container is then responsible for assigning ports for applications when they start up.

One extremely common pattern in an enterprise that manages its own web servers is to host a number of applications in the same container, separating applications by port number (or URL hierarchy) and then using DNS to provide a user-friendly facade around that server. For example, you might have a (virtual or physical) host called appserver, and a number of apps that have been assigned ports 8080 through 8090. Rather than making users remember port numbers, DNS is used to associate a host name like app1 with appserver:8080, app2 with appserver:8081, and so on.

Avoiding Micromanaging Port Assignments

Embracing platform-as-a-service here allows developers and devops alike to not have to perform this kind of micromanagement anymore. Your cloud provider should be managing the port assignment for you because it is likely also managing routing, scaling, high ...