Kubernetes equivalent of env-file in Docker

Question

Background:

Currently we're using Docker and Docker Compose for our services. We have externalized the configuration for different environments into files that define environment variables read by the application. For example a prod.env file:

ENV_VAR_ONE=Something Prod
ENV_VAR_TWO=Something else Prod

and a test.env file:

ENV_VAR_ONE=Something Test
ENV_VAR_TWO=Something else Test

Thus we can simply use the prod.env or test.env file when starting the container:

docker run --env-file prod.env <image>

Our application then picks up its configuration based on the environment variables defined in prod.env.

Questions:

1. Is there a way to provide environment variables from a file in Kubernetes (for example when defining a pod) instead of hardcoding them like this:

apiVersion: v1
kind: Pod
metadata: 
  labels: 
    context: docker-k8s-lab
    name: mysql-pod
  name: mysql-pod
spec: 
  containers: 
    - 
      env: 
        - 
          name: MYSQL_USER
          value: mysql
        - 
          name: MYSQL_PASSWORD
          value: mysql
        - 
          name: MYSQL_DATABASE
          value: sample
        - 
          name: MYSQL_ROOT_PASSWORD
          value: supersecret
      image: "mysql:latest"
      name: mysql
      ports: 
        - 
          containerPort: 3306

2. If this is not possible, what is the suggested approach?

Answer 1

You can populate a container's environment variables through the use of Secrets or ConfigMaps. Use Secrets when the data you are working with is sensitive (e.g. passwords), and ConfigMaps when it is not.

In your Pod definition specify that the container should pull values from a Secret:

apiVersion: v1
kind: Pod
metadata: 
  labels: 
    context: docker-k8s-lab
    name: mysql-pod
  name: mysql-pod
spec: 
  containers:
  - image: "mysql:latest"
    name: mysql
    ports: 
    - containerPort: 3306
    envFrom:
      - secretRef:
         name: mysql-secret

Note that this syntax is only available in Kubernetes 1.6 or later. On an earlier version of Kubernetes you will have to specify each value manually, e.g.:

env: 
- name: MYSQL_USER
  valueFrom:
    secretKeyRef:
      name: mysql-secret
      key: MYSQL_USER

(Note that env take an array as value)

And repeating for every value.

Whichever approach you use, you can now define two different Secrets, one for production and one for dev.

dev-secret.yaml:

apiVersion: v1
kind: Secret
metadata:
  name: mysql-secret
type: Opaque
data:
  MYSQL_USER: bXlzcWwK
  MYSQL_PASSWORD: bXlzcWwK
  MYSQL_DATABASE: c2FtcGxlCg==
  MYSQL_ROOT_PASSWORD: c3VwZXJzZWNyZXQK

prod-secret.yaml:

apiVersion: v1
kind: Secret
metadata:
  name: mysql-secret
type: Opaque
data:
  MYSQL_USER: am9obgo=
  MYSQL_PASSWORD: c2VjdXJlCg==
  MYSQL_DATABASE: cHJvZC1kYgo=
  MYSQL_ROOT_PASSWORD: cm9vdHkK

And deploy the correct secret to the correct Kubernetes cluster:

kubectl config use-context dev
kubectl create -f dev-secret.yaml

kubectl config use-context prod
kubectl create -f prod-secret.yaml

Now whenever a Pod starts it will populate its environment variables from the values specified in the Secret.

Answer 2

A new update for Kubernetes(v1.6) allows what you asked for(years ago).

You can now use the envFrom like this in your yaml file:

  containers:
  - name: django
    image: image/name
    envFrom:
      - secretRef:
         name: prod-secrets

Where development-secrets is your secret, you can create it by:

kubectl create secret generic prod-secrets --from-env-file=prod/env.txt`

Where the txt file content is a key-value:

DB_USER=username_here
DB_PASSWORD=password_here

The docs are still lakes of examples, I had to search really hard on those places:

• Secrets docs, search for --from-file - shows that this option is available.
• The equivalent ConfigMap docs shows an example on how to use it.

Note: there's a difference between --from-file and --from-env-file when creating secret as described in the comments below.

Answer 3

When defining a pod for Kubernetes using a YAML file, there's no direct way to specify a different file containing environment variables for a container. The Kubernetes project says they will improve this area in the future (see Kubernetes docs).

In the meantime, I suggest using a provisioning tool and making the pod YAML a template. For example, using Ansible your pod YAML file would look like:

file my-pod.yaml.template:

apiVersion: v1
kind: Pod
...
spec:
  containers:
  ...
    env:
    - name: MYSQL_ROOT_PASSWORD
      value: {{ mysql_root_pasword }}
    ...

Then your Ansible playbook can specify the variable mysql_root_password somewhere convenient, and substitute it when creating the resource, for example:

file my-playbook.yaml:

- hosts: my_hosts
  vars_files: 
  - my-env-vars-{{ deploy_to }}.yaml
  tasks:
  - name: create pod YAML from template
    template: src=my-pod.yaml.template dst=my-pod.yaml
  - name: create pod in Kubernetes
    command: kubectl create -f my-pod.yaml

file my-env-vars-prod.yaml:

mysql_root_password: supersecret

file my-env-vars-test.yaml:

mysql_root_password: notsosecret

Now you create the pod resource by running, for example:

ansible-playbook -e deploy=test my-playbook.yaml

Answer 4

This works for me:

file env-secret.yaml

apiVersion: v1
kind: Secret
metadata:
  name: env-secret
type: Opaque
stringData:
  .env: |-
    APP_NAME=Laravel
    APP_ENV=local

and into the deployment.yaml or pod.yaml

spec:
  ...
        volumeMounts:
        - name: foo
          mountPath: "/var/www/html/.env"
          subPath: .env
      volumes:
      - name: foo
        secret:
          secretName: env-secret
````

Answer 5

This is an old question but let me describe my answer for future beginner.

You can use kustomize configMapGenerator.

configMapGenerator:
  - name: example
    env: dev.env

and refer this configMap/example in pod definition

Answer 6

I smashed my head aupon tyhis for 2 hours now. I found in the docs a very simple solution to minimize my (and hopefully your) pain.

• Keep env.prod, env.dev as you have them.

• Use a oneliner script to import those into yaml:

  kubectl create configmap my-dev-config --from-env-file=env.dev

  kubectl create configmap my-prod-config --from-env-file=env.prod

You can see the result (for instant gratification):

# You can also save this to disk
kubectl get configmap my-dev-config -o yaml

As a rubyist, I personally find this solution the DRYest as you have a single point to maintain (the ENV bash file, which is compatible with Python/Ruby libraries, ..) and then you YAMLize it in a single execution.

Note that you need to keep your ENV file clean (I have a lot of comments which prevented this to work so had to prepend a cat config.original | egrep -v "^#" | tee config.cleaned) but this doen't change the complexity substantially.

It's all documented here

Answer 7

This is an old question but it has a lot of viewers so I add my answer. The best way to separate the configuration from K8s implementation is using Helm. Each Helm package can have a values.yaml file and we can easily use those values in the Helm chart. If we have a multi-component topology we can create an umbrella Helm package and the parent values package also can overwrite the children values files.