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Configuration

Kubernetes has an integrated pattern for decoupling configuration from application or container.

This pattern makes use of two Kubernetes components: ConfigMaps and Secrets.

Both types of objects hold key-value pairs that can be injected into Pods through a variety of means.

Index

ConfigMaps

A ConfigMap is externalized data stored within Kubernetes that can be referenced through several different means:

  • Environment variable
  • A command line argument (via env var)
  • Injected as a file into a volume mount

ConfigMaps can be created from a manifest, literals, a directory, or from the files the directly.

Exercise: Creating ConfigMaps

Objective: Go over the four methods of creating ConfigMaps.

From Manifest

Create ConfigMap manifest-example from the manifest manifests/cm-manifest.yaml or use the yaml below.

manifests/cm-manifest.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: manifest-example
data:
  city: Ann Arbor
  state: Michigan

Command

$ kubectl create -f manifests/cm-manifest.yaml

View the created ConfigMap.

$ kubectl get configmap manifest-example -o yaml

From Literal

Create ConfigMap literal-example using the --from-literal flag and city=Ann Arbor along with state=Michigan for the values.

$ kubectl create cm literal-example --from-literal="city=Ann Arbor" --from-literal=state=Michigan

View the created ConfigMap.

$ kubectl get cm literal-example -o yaml

From Directory

Create ConfigMap dir-example by using the manifests/cm directory as the source.

$ kubectl create cm dir-example --from-file=manifests/cm/

View the created ConfigMap.

$ kubectl get cm dir-example -o yaml

From File

Create ConfigMap file-example by using the city and state files in the manifests/cm directory.

$ kubectl create cm file-example --from-file=manifests/cm/city --from-file=manifests/cm/state

View the created ConfigMap.

$ kubectl get cm file-example -o yaml

Note: When creating a ConfigMap from a file or directory the content will assume to be multiline as signified by the pipe symbol (|) in the yaml.

Summary: There are four primary methods of creating ConfigMaps with kubectl. From a manifest, passing literals on the command-line, supplying a path to a directory, or to the individual files themselves. These ConfigMaps are stored within etcd, and may be used in a multitude of ways.

Exercise: Using ConfigMaps with Environment Variables

Objective: Dive into how ConfigMap items may be referenced as Environment Variables and how this method may be extended to use them as command-line arguments.

Note: This exercise builds off the previous exercise: Creating ConfigMaps. If you have not, complete it first before continuing.

  1. Create Job cm-env-example using the manifest manifests/cm-env-example.yaml or the yaml below.

manifests/cm-env-example.yaml

apiVersion: batch/v1
kind: Job
metadata:
  name: cm-env-example
spec:
  template:
    spec:
      containers:
      - name: env
        image: alpine:latest
        command: ["/bin/sh", "-c"]
        args: ["printenv CITY"]
        env:
        - name: CITY
          valueFrom:
            configMapKeyRef:
              name: manifest-example
              key: city
      restartPolicy: Never

Command

$ kubectl create -f manifests/cm-env-example.yaml

Note how the Environment Variable is injected using valueFrom and configMapKeyRef. This queries a specific key from the ConfigMap and injects it as an Environment Variable.

  1. List the Pods.
$ kubectl get pods
  1. Copy the pod name and view the output of the Job.
$ kubectl logs cm-env-example-<pod-id>

It should echo the value from the manifest-example ConfigMap city key-value pair.

This same technique can be used to inject the value for use in a Command.

  1. Create another Job cm-cmd-example from the manifest manifests/cm-cmd-example.yaml or use the yaml below.

manifests/cm-cmd-example.yaml

apiVersion: batch/v1
kind: Job
metadata:
  name: cm-cmd-example
spec:
  template:
    spec:
      containers:
      - name: env
        image: alpine:latest
        command: ["/bin/sh", "-c"]
        args: ["echo Hello from ${CITY}!"]
        env:
        - name: CITY
          valueFrom:
            configMapKeyRef:
              name: manifest-example
              key: city
      restartPolicy: Never

Command

$ kubectl create -f manifests/cm-cmd-example.yaml
  1. List the Pods.
$ kubectl get pods
  1. Copy the pod name of the cm-cmd-example job and view the output of the Pod.
$ kubectl logs cm-cmd-example-<pod-id>

It should echo the string "Hello from <data[city]>" referencing the value from the manifest-example ConfigMap.

Summary: Items within a ConfigMap can be injected into a Pod's Environment Variables at container creation. These items may be picked up by the application being run in the container directly, or referenced as a command-line argument. Both methods are commonly used and enable a wide-variety of use-cases.

Clean Up Command:

kubectl delete job cm-env-example cm-cmd-example

Exercise: Using ConfigMaps with Volumes

Objective: Learn how to mount a ConfigMap or specific items stored within a ConfigMap as a volume.

Note: This exercise builds off the previous exercise: Creating ConfigMaps. If you have not, complete it first before continuing.

  1. Create the Pod cm-vol-example using the manifest manifests/cm-vol-example.yaml or use the yaml below.

manifests/cm-vol-example.yaml

apiVersion: v1
kind: Pod
metadata:
  name: cm-vol-example
spec:
  containers:
  - name: mypod
    image: alpine:latest
    command: ["/bin/sh", "-c"]
    args:
    - while true; do
      sleep 10;
      done
    volumeMounts:
    - name: config-volume
      mountPath: /myconfig
    - name: city
      mountPath: /mycity
      readOnly: true
  volumes:
  - name: config-volume
    configMap:
      name: manifest-example
  - name: city
    configMap:
      name: manifest-example
      items:
      - key: city
        path: thisismycity

Command

$ kubectl create -f manifests/cm-vol-example.yaml

Note the volumes and how they are being referenced. The volume city, has an array of items that contains a sub-set of the key-value pairs stored in the manifest-example ConfigMap. When working with the individual items, it is possible to override the name or path to the generated file by supplying an argument for the path parameter.

  1. View the contents of the /myconfig volume mount.
$ kubectl exec cm-vol-example -- ls /myconfig

It will contain two files, matching the names of the keys stored in configMap manifest-example.

  1. cat the contents of the files.
$ kubectl exec cm-vol-example -- /bin/sh -c "cat /myconfig/*"

It will match the values stored in the configMap manifest-example concatenated together.

  1. View the contents of the other Volume Mount mycity.
$ kubectl exec cm-vol-example -- ls /mycity

A file will be present that represents the single item being referenced in the city volume. This file bears the name thisismycity as specified by the path variable.

  1. cat contents of the thisismycity file.
$ kubectl exec cm-vol-example -- cat /mycity/thisismycity

The contents should match the value of data[city].

Summary: In addition to being injected as Environment Variables it's possible to mount the contents of a ConfigMap as a volume. This same method may be augmented to mount specific items from a ConfigMap instead of the entire thing. These items can be renamed or be made read-only to meet a variety of application needs providing an easy to use avenue to further decouple application from configuration.

Clean Up Command:

kubectl delete pod cm-vol-example
kubectl delete cm dir-example file-example literal-example manifest-example

Back to Index

Secrets

A Secret is externalized "private" base64 encoded data stored within Kubernetes that can be referenced through several different means:

  • Environment variable
  • A command line argument (via env var)
  • Injected as a file into a volume mount

Like ConfigMaps, Secrets can be created from a manifest, literals, or from files directly.

Note: For all intents and purposes, Secrets are created and used just like ConfigMaps. If you have completed the ConfigMap Exercises, the Secrets section may be skimmed over glossing a few of the minor syntax differences.

Exercise: Creating Secrets

Objective: Learn to use the four different methods of creating Secrets, and how they different slightly from their ConfigMap counterparts.

From Manifest

Create Secret manifest-example from the manifest manifests/secret-manifest.yaml or use the yaml below.

manifests/secret-manifest.yaml

apiVersion: v1
kind: Secret
metadata:
  name: manifest-example
type: Opaque
data:
  username: ZXhhbXBsZQ==
  password: bXlwYXNzd29yZA==

Command

$ kubectl create -f manifests/secret-manifest.yaml

Note the Secret has the additional attribute type when compared to a ConfigMap. The Opaque value simply means the data is unstructured. Additionally, the content referenced in data itself is base64 encoded. Decoded, they are username=example and password=mypassword.

View the created Secret.

$ kubectl get secret manifest-example -o yaml

From Literal

Create Secret literal-example using the --from-literal flag and username=example along with password=mypassword for the values.

$ kubectl create secret generic literal-example --from-literal=username=example --from-literal=password=mypassword

Note: Unlike ConfigMaps you must also specify the type of Secret you are creating. There are 3 types:

  • docker-registry - Credentials used to interact with a container registry.
  • generic - Eeuivalent to Opaque. Used for unstructured data.
  • tls - A TLS key pair (PEM Format) that accepts a cert (--cert) and key (--key).

View the created Secret.

$ kubectl get secret literal-example -o yaml

From Directory

Create Secret dir-example by using the manifests/secret directory as the source.

$ kubectl create secret generic dir-example --from-file=manifests/secret/

View the created Secret.

$ kubectl get secret dir-example -o yaml

From File

Create ConfigMap file-example by using the username and password files in the manifests/secret directory.

$ kubectl create secret generic  file-example --from-file=manifests/secret/username --from-file=manifests/secret/password

View the created Secret.

$ kubectl get secret file-example -o yaml

Summary: Just like ConfigMaps, there are four primary methods of creating Secrets with kubectl. From manifests and literals to directories and files; no one method is better than another. The fundamental difference when working with Secrets over ConfigMaps, is that they require a type such as generic or opaque and the contents itself is stored in a base64 encoded form.

Exercise: Using Secrets with Environment Variables

Objective: Examine how Secrets may be referenced as Environment Variables and how this may be extended to use them in command-line arguments.

Note: This exercise builds off the previous exercise: Creating Secrets. If you have not, complete it first before continuing.

  1. Create Job secret-env-example using the manifest manifests/secret-env-example.yaml or the yaml below.

manifests/secret-env-example.yaml

apiVersion: batch/v1
kind: Job
metadata:
  name: cm-env-example
spec:
  template:
    spec:
      containers:
      - name: env
        image: alpine:latest
        command: ["/bin/sh", "-c"]
        args: ["printenv USERNAME"]
        env:
        - name: USERNAME
          valueFrom:
            secretKeyRef:
              name: manifest-example
              key: username
      restartPolicy: Never

Command

$ kubectl create -f manifests/secret-env-example.yaml

Note how the Environment Variable is injected using valueFrom and secretKeyRef. This queries a specific key from the Secret and injects it as an Environment Variable.

  1. List the Pods.
$ kubectl get pods
  1. Copy the pod name and view the output of the Job.
$ kubectl logs secret-env-example-<pod-id>

It should echo the value from the manifest-example Secret username key-value pair.

This same technique can be used to inject the value for use in a Command.

  1. Create another Job secret-cmd-example from the manifest manifests/secret-cmd-example.yaml or use the yaml below.

manifests/secret-cmd-example.yaml

apiVersion: batch/v1
kind: Job
metadata:
  name: secret-cmd-example
spec:
  template:
    spec:
      containers:
      - name: env
        image: alpine:latest
        command: ["/bin/sh", "-c"]
        args: ["echo Hello there ${USERNAME}!"]
        env:
        - name: USERNAME
          valueFrom:
            secretKeyRef:
              name: manifest-example
              key: username
      restartPolicy: Never

Command

$ kubectl create -f manifests/secret-cmd-example.yaml
  1. List the Pods.
$ kubectl get pods
  1. Copy the pod name of the secret-cmd-example job and view the output of the Pod.
$ kubectl logs secret-cmd-example-<pod-id>

It should echo the string "Hello there <data[username]>!" referencing the value from the manifest-example Secret.

Summary: Secrets may be injected into a Pod's Environment Variables at container creation. These variables may be picked up by the application being run in the container directly, or referenced as a command-line argument. Both methods are useful in a wide-variety of scenarios enabling further decoupling of application and configuration.

Clean Up Command:

kubectl delete job secret-env-example secret-cmd-example

Exercise: Using Secrets with Volumes

Objective: Learn how to mount a Secret or specific items stored within a Secret as a volume.

Note: This exercise builds off the previous exercise: Creating Secrets. If you have not, complete it first before continuing.

  1. Create the Pod secret-vol-example using the manifest manifests/secret-vol-example.yaml or use the yaml below.

manifests/secret-vol-example.yaml

apiVersion: v1
kind: Pod
metadata:
  name: secret-vol-example
spec:
  containers:
  - name: mypod
    image: alpine:latest
    command: ["/bin/sh", "-c"]
    args:
    - while true; do
      sleep 10;
      done
    volumeMounts:
    - name: secret-volume
      mountPath: /mysecret
    - name: password
      mountPath: /mypass
      readOnly: true
  volumes:
  - name: secret-volume
    secret:
      secretName: manifest-example
  - name: password
    secret:
      secretName: manifest-example
      items:
      - key: password
        path: supersecretpass

Command

$ kubectl create -f manifests/secret-vol-example.yaml

Note the volumes and how they are being referenced. The volume password, has an array of items that contains a sub-set of the key-value pairs stored in the manifest-example Secret. When working with the individual items, it is possible to override the name or path to the generated file by supplying an argument for the path parameter.

  1. View the contents of the /mysecret volume mount.
$ kubectl exec secret-vol-example -- ls /mysecret

It will contain two files, matching the names of the keys stored in Secret manifest-example.

  1. cat the contents of the files.
$ kubectl exec secret-vol-example -- /bin/sh -c "cat /mysecret/*"

It will match the values stored in the Secret manifest-example concatenated together.

  1. View the contents of the other Volume Mount mypass.
$ kubectl exec secret-vol-example -- ls /mypass

A file will be present that represents the single item being referenced in the password volume. This file bears the name supersecretpass as specified by the path variable.

  1. cat contents of the supersecretpass file.
$ kubectl exec secret-vol-example -- cat /mypass/supersecretpass

The contents should match the value of data[password].

Summary: Secrets can be consumed in multiple ways. One of the more flexible (and secure) methods being mounting as a volume. It's possible to mount the entire contents of a Secret as a volume, or alternatively mount specific items stored in a Secret. These items can be renamed or be made read-only to meet a variety of application needs.

Clean Up Command:

kubectl delete pod secret-vol-example
kubectl delete secret dir-example file-example literal-example manifest-example

Back to Index

Cleaning Up

kubectl delete cm manifest-example literal-example dir-example file-example
kubectl delete secret manifest-example literal-example dir-example file-example

Back to Index

Helpful Resources

Back to Index