ConfigMap, Secret

In Kubernetes, how can we handle situations where a pod's development environment is divided into dev and prod, or security connection (SSH) settings have different values for each environment, such as false on a development server and true in production?

This implies running different containers, but since there might be common values, configuring each one individually and deploying them as new containers would be cumbersome.

A feature is needed to provide necessary environment configurations separately from the containers.

Therefore, ConfigMap allows us to define and manage these environment settings externally from the containers.

ConfigMap stores data in a Key-Value format. (Since both key and value are stored as strings, even boolean values like false must be enclosed in quotes, like 'false'.)

Secret is similar to ConfigMap, but its values must be encoded.

Defining ConfigMap #

The example below defines database configuration files as a ConfigMap.

apiVersion: v1
kind: ConfigMap
metadata:
  name: config-dev
  namespace: default
data:
  DB_URL: localhost
  DB_USER: myuser
  DB_PASS: mypass
  DEBUG_INFO: debug

• Data can be stored in key-value format under data.

There are two ways to define data in a ConfigMap: you can directly input key-value pairs as constants, or you can use a file as the ConfigMap's value.

Key-value format can be defined as shown above.

Defining with a File #

When defining with a file, assuming you've created a file.txt file:

kubectl create configmap dev-file --from-file=./file.txt

As shown above, you specify the ConfigMap's name and the file from which to retrieve values.

A Secret is created as follows:

kubectl create secret generic sec-file --from-file=./file2.txt

A point to note here is that the content of the .txt file should not be encoded. Encoding occurs the moment the command is entered, so if the .txt file already contains encoded content, it will be double-encoded, causing issues.

Using ConfigMap #

Let's use the ConfigMap defined above. You can define the pod in a YAML file as follows:

apiVersion: v1
kind: Pod
metadata:
  name: pod-name
spec:
  containers:
  - name: container-name
    valueFrom:
      configMapKeyRef:
        name: dev-file
        key: file.txt
  - name: container2-name
    valueFrom:
      secretKeyRef:
        name: sec-file
        key: file2.txt

Values are retrieved via valueFrom, and the key is specified. If envFrom is used, it retrieves key-value pairs in environment variable format.

Mounting to a Volume #

apiVersion: v1
kind: Pod
metadata:
  name: pod-name
spec:
  containers:
  - name: container-name
    image: tmkube/init
    volumeMounts:
    - name: file-volume
      mountPath: /mount
  volumes:
  - name: file-volume
    configMap:
      name: dev-file

You can also mount ConfigMap data to a volume as shown above.

You can retrieve values one by one using env:, or use envFrom to retrieve all of them.