Config Maps

• Setting environment variables to container template is one option to send configuration to container.
• But if configuration differ from environment to environment like DEV, QA, PROD then setting configuration value on env may not be a good idea.
• Kubernetes has a resource called ConfigMaps which treats configuration as a separate object.
• So each environment can have same objects, but different values.

ConfigMaps YAML

• Let's create simple ConfigMaps that stores our GREETING and NAME environment variable value.

apiVersion: v1
kind: ConfigMap
metadata:
  name: web
data:
  GREETING: Namaste
  NAME: Friends!!! 

• As you can see creating ConfigMap is simple.
• You set kind as ConfigMap.
• You set name of ConfigMap on metadata section.
• On data root node, you add your properties values.
• It is just a key value pair.
• Here we are setting GREETING as Namaste and NAME as Friends!!!

Creating ConfigMap

• Creating a ConfigMap is simple too, you just use your handy kubectl create command.

kubectl create -f configmap.yaml

Using ConfigMap with env property

• If you want to get specific environment variable value using ConfigMap you can use valueFrom property instead of value property.

apiVersion: apps/v1
kind: Deployment
# metadata
spec:
  # replicas & selector
  template:
    # metadata
    spec:
      containers:
        - image: amantuladhar/docker-kubernetes:environment
          name: web
          env:
            - name: GREETING
              valueFrom:
                configMapKeyRef:
                  name: web # Name of ConfigMaps
                  key: GREETING
            - name: NAME
              valueFrom:
                configMapKeyRef:
                  name: web # Name of ConfigMaps
                  key: NAME
          # probes & ports

• In above file, you can see we are using valueFrom property instead of value.
• Using configMapKeyRef tells Kubernetes to search in ConfigMap.
• configMapKeyRef.name states the name of the ConfigMap resource.
• configMapKeyRef.key states which key to look for in defined resource.
• Run the app using above configuration and call your endpoint

➜  http $(minikube service web --url)/test
HTTP/1.1 200
Content-Type: application/json;charset=UTF-8
Date: Wed, 27 Feb 2019 02:00:50 GMT
Transfer-Encoding: chunked

{
    "app.version": "v1-web",
    "host.address": "172.17.0.6",
    "message": "Namaste Friends!!!"
}

• Now our message has Namaste Friends!!!.
• That's the value we have in our ConfigMaps

Updating ConfigMap

Note: Updating ConfigMap doesn't update the value a running container has.

If you change value of ConfigMap, two similar container might be in inconsistent state.

• You can update the ConfigMap values using kubectl patch command.

kubectl patch configmaps web --patch '{"data": {"GREETING": "Yo"}}'

Import All values from ConfigMap

• While previous method gave us power to pull in value from ConfigMap.
• It was troublesome, if we have let's say 20 properties, we have to use valueFrom 20 times.
• Kubernetes has another property envFrom which allows you to import all values from ConfigMaps

apiVersion: apps/v1
kind: Deployment
# metadata
spec:
  # replicas & selector
  template:
    # metadata:
    spec:
      containers:
        - image: amantuladhar/docker-kubernetes:environment
          name: web
          envFrom:
            - configMapRef:
                name: web
          # probe and port

• In above example, we are using envFrom instead of env.
• When we use envFrom property, we import all properties from that resource. (But there is limitation)
• We can also use prefix keyword if you want to prefix your configuration properties with something. env.prefix
• If any of your ConfigMap property has dash -. That won't be imported.
• Because environment variable with dash - are invalid.
• Kubernetes doesn't do any post-processing for you in this case.

There one more way to load the ConfigMaps i.e. using volumes

We don't know how to mount the volumes yet, so this will be skipped for now.