Converting ConfigMap Output into Environment Variables

Altering the perpetual process#

All the examples we’ve seen so far are differing only in the source. The destination is always the same. No matter whether ConfigMap is created from a file, from a directory, from literal values, or from an environment file, it perpetually resulted in one or more files being injected into a container.

This time we’ll try something different. We’ll see how we can convert a ConfigMap into environment variables.

Looking into first definition#

Let’s take a look at a sample definition of alpine-env.yml file.

The major difference, when compared with alpine.yml, is that volumeMounts and volumes sections are gone. This time we have an env section.

Instead of a value field, we have valueFrom. Further on, we declared that it should get values from a ConfigMap (configMapKeyRef) named my-config. Since that ConfigMap has multiple values, we specified the key as well.

Creating the pod#

Let’s create the Pod.

We created the Pod and executed the env command inside its only container. The output of the latter command, limited to the relevant parts, is as follows.

There’s another, often more useful way to specify environment variables from a ConfigMap. Before we try it, we’ll remove the currently running Pod.

Looking Into Second Definition#

Let’s take a look at yet another definition alpine-env-all.yml.

The difference is only in the way environment variables are defined.

This time, the syntax is much shorter. We have envFrom, instead of the env section. It can be either configMapRef or secretRef. Since we did not yet explore Secrets, we’ll stick with the prior. Inside configMapRef is the name reference to the my-config ConfigMap.

Creating the Pod#

Let’s see it in action.

We created the Pod and retrieved all the environment variables from inside its only container. The output of the latter command, limited to the relevant parts, is as follows.

The result is the same as before. The difference is only in the way we define environment variables.

With env.valueFrom.configMapKeyRef syntax, we need to specify each ConfigMap key separately. That gives us control over the scope and the relation with the names of container variables.

The envFrom.configMapRef converts all ConfigMap’s data into environment variables. That is often a better and simpler option if you don’t need to use different names between ConfigMap and environment variable keys. The syntax is short, and we don’t need to worry whether we forgot to include one of the ConfigMap’s keys.

Try it yourself#

A list of all the commands used in the lesson is given below.