Environment Variable

  • Most of the apps that we develop nowadays depends on some kind of environment variables / configuration files.
  • Using configuration files on containers are a bit tricky.
  • If we push the configuration with container itself, we need to update / build the image every time we change the container.
  • Often times some configuration properties are secret. We don't want some properties to be passed on carelessly.
  • Containers normally use environment variables to get configuration.
  • Kubernetes also supports passing environment variables to containers.

Kubernetes doesn't allow Pod level environment. Environment variables are set on container level.

  • We cannot modify the environment variable for a container once it is set.
  • We can dispose the current container and re-create a new one.
  • If you think about the solution above, it make sense right!
  • Containers are supposed to be immutable, if you change configuration of one container other replicas may not have same configuration.
  • At least until you make changes to all of them.

Example

  • Let's create a Deployment that sets environment variable to container.
apiVersion: apps/v1
kind: Deployment
metadata:
  # metadata
spec:
  # replica & matchLabel selector
  template:
    metadata:
      # metadata
    spec:
      containers:
        - image: amantuladhar/docker-kubernetes:environment   #1
          name: web
          env:                     #2
            - name: GREETING       #3
              value: Namaste       #4
            - name: NAME           #3
              value: Folks!!       #4
          # probe properties
  • #1 - We are using new image i.e docker-kubernetes:environment. I have modified the endpoint so that it changes the message based on environment variables.
    • GREETING - Default is Hello
    • NAME - Default is Fellas!!
  • #2 - We use env properties to set the environment variable to container.
  • #3 - Name of environment variable you want to set
  • #4 - Value of environment variable you want to set

Calling Endpoint

➜ http $(minikube service web --url)/test
HTTP/1.1 200
Content-Type: application/json;charset=UTF-8
Date: Tue, 26 Feb 2019 05:47:37 GMT
Transfer-Encoding: chunked

{
    "app.version": "v1-web",
    "host.address": "172.17.0.7",
    "message": "Namaste Folks!!"
}

Updating environment variable

  • Note: To change the environment variable of container, either you need to restart the container
  • You can update the environment variable easily with command below, but it will restart the container.
kubectl set env deployment web GREETING="Adios"
  • kubectl set env @resource @name @env_var=@env_value
  • If you want to unset environment variable
kubectl set env deployment web GREETING-
  • If you use environment variable and use dash - it will unset the environment variable.