Kubernetes: Up and Running, 3rd Edition

Chapter 13. ConfigMaps and Secrets

It’s good practice to make container images as reusable as possible. The same image should be able to be used for development, staging, and production. It’s even better if the same image is general-purpose enough to be used across applications and services. Testing and versioning are more risky and complicated if images need to be re-created for each new environment. How then do we specialize the use of that image at runtime?

This is where ConfigMaps and Secrets come into play. ConfigMaps are used to provide configuration information for workloads. This can be either fine-grained information like a string or a composite value in the form of a file. Secrets are similar to ConfigMaps but focus on making sensitive information available to the workload. They can be used for things like credentials or TLS certificates.

ConfigMaps

One way to think of a ConfigMap is as a Kubernetes object that defines a small filesystem. Another way is as a set of variables that can be used when defining the environment or command line for your containers. The key thing to note is that the ConfigMap is combined with the Pod right before it is run. This means that the container image and the Pod definition can be reused by many workloads just by changing the ConfigMap that is used.

Creating ConfigMaps

Let’s jump right in and create a ConfigMap. Like many objects in Kubernetes, you can create these in an immediate, imperative way, or you can create them from a manifest ...