2.3.1 OpenShift image requirements

Mon, 01 Jan 0001 00:00:00 +0000

Task 2.3.1.1: Additional requirements

OpenShift has additional security features enabled in comparison to Docker or a vanilla Kubernetes plattform. The most relevant mechanism are prevention of root user, SELinux enabled and arbitrary user ids.

This adds additional requirements to the container images that will be deployed to OpenShift. This lab shows how to deal with them.

Task 2.3.1.2: Demo application

We use a Go application running a HTTP server listening on port 8080. Every request is logged with the actual time and the client IP address. The log file is placed under /home/golang/hello-go.log.

2.3.2 Best practices

Mon, 01 Jan 0001 00:00:00 +0000

Here you find best practices. It is not a lab to play through.

Best practices for container in general

Best practices for writing Dockerfiles

One process per container

It is recommended to start only one process per container. This simplifies the following things.

Docker can recognize if your container failed and restart it if needed
Reduce Image size and startup time
Signal handling flows are clearer
Reusable Images and looser coupling

Instructions order

The order of the Docker instruction matters. When a single Layer becomes invalid, because of changing files or modifying lines in the Dockerfile, the subsequent layers become invalid too. As a rule of thumb: Order your steps from least to most frequently changing steps to optimize caching.