ConfigMaps: Environment Variables and Volume Mounts

Configuration and Security / Guide 24 of 44 / Beginner

• Kubernetes1.36.4
• Cluster4 nodes
• Runtimecontainerd 2.2.6
• CNICalico v3.32.1
• TimeAbout 16 min

--from-env-file reads KEY=value lines and makes one ConfigMap key per line; --from-file makes ONE key whose name is the filename and whose value is the whole file. Mixing those two up is the usual reason a mounted config file arrives as a directory of fragments or a single unusable blob.

This guide includes

Use this when configuration has to reach a container and the task names one particular way. This matters because there are three ways to create a ConfigMap and four ways to consume one - and a missing key fails differently depending on which you chose.

• creating a ConfigMap three ways - from literals, from a file, and from an env-file
• consuming one four ways inside a single Pod, all visible in one log
• referencing a key that does not exist, and seeing the Pod wait rather than crash
• adding optional: true to that same reference and watching it start

Before you start

• A cluster and kubectl.
• The session creates namespace ckad-cm with three ConfigMaps built three different ways, and four Pods that consume them.

1. 1

   Three ways to create one

2. 2

   Four ways to consume one

3. 3

   The key that is not there

4. 4

   optional makes it tolerable

Official sources

• ConfigMaps
• Configure a Pod to Use a ConfigMap
• Define Environment Variables for a Container