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Inject Data Into Applications

Specify configuration and other data for the Pods that run your workload.

1: Define a Command and Arguments for a Container
2: Define Dependent Environment Variables
3: Define Environment Variables for a Container
4: Expose Pod Information to Containers Through Environment Variables
5: Expose Pod Information to Containers Through Files
6: Distribute Credentials Securely Using Secrets

1 - Define a Command and Arguments for a Container

This page shows how to define commands and arguments when you run a container in a Pod.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

To check the version, enter kubectl version.

Define a command and arguments when you create a Pod

When you create a Pod, you can define a command and arguments for the containers that run in the Pod. To define a command, include the command field in the configuration file. To define arguments for the command, include the args field in the configuration file. The command and arguments that you define cannot be changed after the Pod is created.

The command and arguments that you define in the configuration file override the default command and arguments provided by the container image. If you define args, but do not define a command, the default command is used with your new arguments.

Note: The command field corresponds to entrypoint in some container runtimes.

In this exercise, you create a Pod that runs one container. The configuration file for the Pod defines a command and two arguments:

pods/commands.yaml

apiVersion: v1
kind: Pod
metadata:
  name: command-demo
  labels:
    purpose: demonstrate-command
spec:
  containers:
  - name: command-demo-container
    image: debian
    command: ["printenv"]
    args: ["HOSTNAME", "KUBERNETES_PORT"]
  restartPolicy: OnFailure

Create a Pod based on the YAML configuration file:

kubectl apply -f https://k8s.io/examples/pods/commands.yaml

List the running Pods:
```
kubectl get pods
```
The output shows that the container that ran in the command-demo Pod has completed.
To see the output of the command that ran in the container, view the logs from the Pod:
```
kubectl logs command-demo
```
The output shows the values of the HOSTNAME and KUBERNETES_PORT environment variables:
```
command-demo
tcp://10.3.240.1:443
```

Use environment variables to define arguments

In the preceding example, you defined the arguments directly by providing strings. As an alternative to providing strings directly, you can define arguments by using environment variables:

env:
- name: MESSAGE
  value: "hello world"
command: ["/bin/echo"]
args: ["$(MESSAGE)"]

This means you can define an argument for a Pod using any of the techniques available for defining environment variables, including ConfigMaps and Secrets.

Note: The environment variable appears in parentheses, "$(VAR)". This is required for the variable to be expanded in the command or args field.

Run a command in a shell

In some cases, you need your command to run in a shell. For example, your command might consist of several commands piped together, or it might be a shell script. To run your command in a shell, wrap it like this:

command: ["/bin/sh"]
args: ["-c", "while true; do echo hello; sleep 10;done"]

What's next

Learn more about configuring pods and containers.
Learn more about running commands in a container.
See Container.

2 - Define Dependent Environment Variables

This page shows how to define dependent environment variables for a container in a Kubernetes Pod.

Before you begin

Define an environment dependent variable for a container

When you create a Pod, you can set dependent environment variables for the containers that run in the Pod. To set dependent environment variables, you can use $(VAR_NAME) in the value of env in the configuration file.

In this exercise, you create a Pod that runs one container. The configuration file for the Pod defines a dependent environment variable with common usage defined. Here is the configuration manifest for the Pod:

pods/inject/dependent-envars.yaml

apiVersion: v1
kind: Pod
metadata:
  name: dependent-envars-demo
spec:
  containers:
    - name: dependent-envars-demo
      args:
        - while true; do echo -en '\n'; printf UNCHANGED_REFERENCE=$UNCHANGED_REFERENCE'\n'; printf SERVICE_ADDRESS=$SERVICE_ADDRESS'\n';printf ESCAPED_REFERENCE=$ESCAPED_REFERENCE'\n'; sleep 30; done;
      command:
        - sh
        - -c
      image: busybox:1.28
      env:
        - name: SERVICE_PORT
          value: "80"
        - name: SERVICE_IP
          value: "172.17.0.1"
        - name: UNCHANGED_REFERENCE
          value: "$(PROTOCOL)://$(SERVICE_IP):$(SERVICE_PORT)"
        - name: PROTOCOL
          value: "https"
        - name: SERVICE_ADDRESS
          value: "$(PROTOCOL)://$(SERVICE_IP):$(SERVICE_PORT)"
        - name: ESCAPED_REFERENCE
          value: "$$(PROTOCOL)://$(SERVICE_IP):$(SERVICE_PORT)"

Create a Pod based on that manifest:

kubectl apply -f https://k8s.io/examples/pods/inject/dependent-envars.yaml

pod/dependent-envars-demo created

List the running Pods:

kubectl get pods dependent-envars-demo

NAME                      READY     STATUS    RESTARTS   AGE
dependent-envars-demo     1/1       Running   0          9s

Check the logs for the container running in your Pod:

kubectl logs pod/dependent-envars-demo


UNCHANGED_REFERENCE=$(PROTOCOL)://172.17.0.1:80
SERVICE_ADDRESS=https://172.17.0.1:80
ESCAPED_REFERENCE=$(PROTOCOL)://172.17.0.1:80

As shown above, you have defined the correct dependency reference of SERVICE_ADDRESS, bad dependency reference of UNCHANGED_REFERENCE and skip dependent references of ESCAPED_REFERENCE.

When an environment variable is already defined when being referenced, the reference can be correctly resolved, such as in the SERVICE_ADDRESS case.

Note that order matters in the env list. An environment variable is not considered "defined" if it is specified further down the list. That is why UNCHANGED_REFERENCE fails to resolve $(PROTOCOL) in the example above.

When the environment variable is undefined or only includes some variables, the undefined environment variable is treated as a normal string, such as UNCHANGED_REFERENCE. Note that incorrectly parsed environment variables, in general, will not block the container from starting.

The $(VAR_NAME) syntax can be escaped with a double $, ie: $$(VAR_NAME). Escaped references are never expanded, regardless of whether the referenced variable is defined or not. This can be seen from the ESCAPED_REFERENCE case above.

What's next

Learn more about environment variables.
See EnvVarSource.

3 - Define Environment Variables for a Container

This page shows how to define environment variables for a container in a Kubernetes Pod.

Before you begin

Define an environment variable for a container

When you create a Pod, you can set environment variables for the containers that run in the Pod. To set environment variables, include the env or envFrom field in the configuration file.

The env and envFrom fields have different effects.

env: allows you to set environment variables for a container, specifying a value directly for each variable that you name.
envFrom: allows you to set environment variables for a container by referencing either a ConfigMap or a Secret. When you use envFrom, all the key-value pairs in the referenced ConfigMap or Secret are set as environment variables for the container. You can also specify a common prefix string.

You can read more about ConfigMap and Secret.

This page explains how to use env.

In this exercise, you create a Pod that runs one container. The configuration file for the Pod defines an environment variable with name DEMO_GREETING and value "Hello from the environment". Here is the configuration manifest for the Pod:

pods/inject/envars.yaml

apiVersion: v1
kind: Pod
metadata:
  name: envar-demo
  labels:
    purpose: demonstrate-envars
spec:
  containers:
  - name: envar-demo-container
    image: gcr.io/google-samples/node-hello:1.0
    env:
    - name: DEMO_GREETING
      value: "Hello from the environment"
    - name: DEMO_FAREWELL
      value: "Such a sweet sorrow"

Create a Pod based on that manifest:

kubectl apply -f https://k8s.io/examples/pods/inject/envars.yaml

List the running Pods:

kubectl get pods -l purpose=demonstrate-envars

The output is similar to:

NAME            READY     STATUS    RESTARTS   AGE
envar-demo      1/1       Running   0          9s

List the Pod's container environment variables:

kubectl exec envar-demo -- printenv

The output is similar to this:

NODE_VERSION=4.4.2
EXAMPLE_SERVICE_PORT_8080_TCP_ADDR=10.3.245.237
HOSTNAME=envar-demo
...
DEMO_GREETING=Hello from the environment
DEMO_FAREWELL=Such a sweet sorrow

Note: The environment variables set using the env or envFrom field override any environment variables specified in the container image.

Note: Environment variables may reference each other, however ordering is important. Variables making use of others defined in the same context must come later in the list. Similarly, avoid circular references.

Using environment variables inside of your config

Environment variables that you define in a Pod's configuration under .spec.containers[*].env[*] can be used elsewhere in the configuration, for example in commands and arguments that you set for the Pod's containers. In the example configuration below, the GREETING, HONORIFIC, and NAME environment variables are set to Warm greetings to, The Most Honorable, and Kubernetes, respectively. The environment variable MESSAGE combines the set of all these environment variables and then uses it as a CLI argument passed to the env-print-demo container.

Environment variable names consist of letters, numbers, underscores, dots, or hyphens, but the first character cannot be a digit. If the RelaxedEnvironmentVariableValidation feature gate is enabled, all printable ASCII characters except "=" may be used for environment variable names.

apiVersion: v1
kind: Pod
metadata:
  name: print-greeting
spec:
  containers:
  - name: env-print-demo
    image: bash
    env:
    - name: GREETING
      value: "Warm greetings to"
    - name: HONORIFIC
      value: "The Most Honorable"
    - name: NAME
      value: "Kubernetes"
    - name: MESSAGE
      value: "$(GREETING) $(HONORIFIC) $(NAME)"
    command: ["echo"]
    args: ["$(MESSAGE)"]

Upon creation, the command echo Warm greetings to The Most Honorable Kubernetes is run on the container.

What's next

Learn more about environment variables.
Learn about using secrets as environment variables.
See EnvVarSource.

4 - Expose Pod Information to Containers Through Environment Variables

This page shows how a Pod can use environment variables to expose information about itself to containers running in the Pod, using the downward API. You can use environment variables to expose Pod fields, container fields, or both.

In Kubernetes, there are two ways to expose Pod and container fields to a running container:

Environment variables, as explained in this task
Volume files

Together, these two ways of exposing Pod and container fields are called the downward API.

As Services are the primary mode of communication between containerized applications managed by Kubernetes, it is helpful to be able to discover them at runtime.

Read more about accessing Services here.

Before you begin

Use Pod fields as values for environment variables

In this part of exercise, you create a Pod that has one container, and you project Pod-level fields into the running container as environment variables.

pods/inject/dapi-envars-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: dapi-envars-fieldref
spec:
  containers:
    - name: test-container
      image: registry.k8s.io/busybox
      command: [ "sh", "-c"]
      args:
      - while true; do
          echo -en '\n';
          printenv MY_NODE_NAME MY_POD_NAME MY_POD_NAMESPACE;
          printenv MY_POD_IP MY_POD_SERVICE_ACCOUNT;
          sleep 10;
        done;
      env:
        - name: MY_NODE_NAME
          valueFrom:
            fieldRef:
              fieldPath: spec.nodeName
        - name: MY_POD_NAME
          valueFrom:
            fieldRef:
              fieldPath: metadata.name
        - name: MY_POD_NAMESPACE
          valueFrom:
            fieldRef:
              fieldPath: metadata.namespace
        - name: MY_POD_IP
          valueFrom:
            fieldRef:
              fieldPath: status.podIP
        - name: MY_POD_SERVICE_ACCOUNT
          valueFrom:
            fieldRef:
              fieldPath: spec.serviceAccountName
  restartPolicy: Never

In that manifest, you can see five environment variables. The env field is an array of environment variable definitions. The first element in the array specifies that the MY_NODE_NAME environment variable gets its value from the Pod's spec.nodeName field. Similarly, the other environment variables get their names from Pod fields.

Note: The fields in this example are Pod fields. They are not fields of the container in the Pod.

Create the Pod:

kubectl apply -f https://k8s.io/examples/pods/inject/dapi-envars-pod.yaml

Verify that the container in the Pod is running:

# If the new Pod isn't yet healthy, rerun this command a few times.
kubectl get pods

View the container's logs:

kubectl logs dapi-envars-fieldref

The output shows the values of selected environment variables:

minikube
dapi-envars-fieldref
default
172.17.0.4
default

To see why these values are in the log, look at the command and args fields in the configuration file. When the container starts, it writes the values of five environment variables to stdout. It repeats this every ten seconds.

Next, get a shell into the container that is running in your Pod:

kubectl exec -it dapi-envars-fieldref -- sh

In your shell, view the environment variables:

# Run this in a shell inside the container
printenv

The output shows that certain environment variables have been assigned the values of Pod fields:

MY_POD_SERVICE_ACCOUNT=default
...
MY_POD_NAMESPACE=default
MY_POD_IP=172.17.0.4
...
MY_NODE_NAME=minikube
...
MY_POD_NAME=dapi-envars-fieldref

Use container fields as values for environment variables

In the preceding exercise, you used information from Pod-level fields as the values for environment variables. In this next exercise, you are going to pass fields that are part of the Pod definition, but taken from the specific container rather than from the Pod overall.

Here is a manifest for another Pod that again has just one container:

pods/inject/dapi-envars-container.yaml

apiVersion: v1
kind: Pod
metadata:
  name: dapi-envars-resourcefieldref
spec:
  containers:
    - name: test-container
      image: registry.k8s.io/busybox:1.24
      command: [ "sh", "-c"]
      args:
      - while true; do
          echo -en '\n';
          printenv MY_CPU_REQUEST MY_CPU_LIMIT;
          printenv MY_MEM_REQUEST MY_MEM_LIMIT;
          sleep 10;
        done;
      resources:
        requests:
          memory: "32Mi"
          cpu: "125m"
        limits:
          memory: "64Mi"
          cpu: "250m"
      env:
        - name: MY_CPU_REQUEST
          valueFrom:
            resourceFieldRef:
              containerName: test-container
              resource: requests.cpu
        - name: MY_CPU_LIMIT
          valueFrom:
            resourceFieldRef:
              containerName: test-container
              resource: limits.cpu
        - name: MY_MEM_REQUEST
          valueFrom:
            resourceFieldRef:
              containerName: test-container
              resource: requests.memory
        - name: MY_MEM_LIMIT
          valueFrom:
            resourceFieldRef:
              containerName: test-container
              resource: limits.memory
  restartPolicy: Never

In this manifest, you can see four environment variables. The env field is an array of environment variable definitions. The first element in the array specifies that the MY_CPU_REQUEST environment variable gets its value from the requests.cpu field of a container named test-container. Similarly, the other environment variables get their values from fields that are specific to this container.

Create the Pod:

kubectl apply -f https://k8s.io/examples/pods/inject/dapi-envars-container.yaml

Verify that the container in the Pod is running:

# If the new Pod isn't yet healthy, rerun this command a few times.
kubectl get pods

View the container's logs:

kubectl logs dapi-envars-resourcefieldref

The output shows the values of selected environment variables:

What's next

Read Defining Environment Variables for a Container
Read the spec API definition for Pod. This includes the definition of Container (part of Pod).
Read the list of available fields that you can expose using the downward API.

Read about Pods, containers and environment variables in the legacy API reference:

5 - Expose Pod Information to Containers Through Files

This page shows how a Pod can use a downwardAPI volume, to expose information about itself to containers running in the Pod. A downwardAPI volume can expose Pod fields and container fields.

In Kubernetes, there are two ways to expose Pod and container fields to a running container:

Environment variables
Volume files, as explained in this task

Together, these two ways of exposing Pod and container fields are called the downward API.

Before you begin

Store Pod fields

In this part of exercise, you create a Pod that has one container, and you project Pod-level fields into the running container as files. Here is the manifest for the Pod:

pods/inject/dapi-volume.yaml

apiVersion: v1
kind: Pod
metadata:
  name: kubernetes-downwardapi-volume-example
  labels:
    zone: us-est-coast
    cluster: test-cluster1
    rack: rack-22
  annotations:
    build: two
    builder: john-doe
spec:
  containers:
    - name: client-container
      image: registry.k8s.io/busybox
      command: ["sh", "-c"]
      args:
      - while true; do
          if [[ -e /etc/podinfo/labels ]]; then
            echo -en '\n\n'; cat /etc/podinfo/labels; fi;
          if [[ -e /etc/podinfo/annotations ]]; then
            echo -en '\n\n'; cat /etc/podinfo/annotations; fi;
          sleep 5;
        done;
      volumeMounts:
        - name: podinfo
          mountPath: /etc/podinfo
  volumes:
    - name: podinfo
      downwardAPI:
        items:
          - path: "labels"
            fieldRef:
              fieldPath: metadata.labels
          - path: "annotations"
            fieldRef:
              fieldPath: metadata.annotations

In the manifest, you can see that the Pod has a downwardAPI Volume, and the container mounts the volume at /etc/podinfo.

Look at the items array under downwardAPI. Each element of the array defines a downwardAPI volume. The first element specifies that the value of the Pod's metadata.labels field should be stored in a file named labels. The second element specifies that the value of the Pod's annotations field should be stored in a file named annotations.

Note: The fields in this example are Pod fields. They are not fields of the container in the Pod.

Create the Pod:

kubectl apply -f https://k8s.io/examples/pods/inject/dapi-volume.yaml

Verify that the container in the Pod is running:

kubectl get pods

View the container's logs:

kubectl logs kubernetes-downwardapi-volume-example

The output shows the contents of the labels file and the annotations file:

cluster="test-cluster1"
rack="rack-22"
zone="us-est-coast"

build="two"
builder="john-doe"

Get a shell into the container that is running in your Pod:

kubectl exec -it kubernetes-downwardapi-volume-example -- sh

In your shell, view the labels file:

/# cat /etc/podinfo/labels

The output shows that all of the Pod's labels have been written to the labels file:

cluster="test-cluster1"
rack="rack-22"
zone="us-est-coast"

Similarly, view the annotations file:

/# cat /etc/podinfo/annotations

View the files in the /etc/podinfo directory:

/# ls -laR /etc/podinfo

In the output, you can see that the labels and annotations files are in a temporary subdirectory: in this example, ..2982_06_02_21_47_53.299460680. In the /etc/podinfo directory, ..data is a symbolic link to the temporary subdirectory. Also in the /etc/podinfo directory, labels and annotations are symbolic links.

drwxr-xr-x  ... Feb 6 21:47 ..2982_06_02_21_47_53.299460680
lrwxrwxrwx  ... Feb 6 21:47 ..data -> ..2982_06_02_21_47_53.299460680
lrwxrwxrwx  ... Feb 6 21:47 annotations -> ..data/annotations
lrwxrwxrwx  ... Feb 6 21:47 labels -> ..data/labels

/etc/..2982_06_02_21_47_53.299460680:
total 8
-rw-r--r--  ... Feb  6 21:47 annotations
-rw-r--r--  ... Feb  6 21:47 labels

Using symbolic links enables dynamic atomic refresh of the metadata; updates are written to a new temporary directory, and the ..data symlink is updated atomically using rename(2).

Note: A container using Downward API as a subPath volume mount will not receive Downward API updates.

Exit the shell:

/# exit

Store container fields

The preceding exercise, you made Pod-level fields accessible using the downward API. In this next exercise, you are going to pass fields that are part of the Pod definition, but taken from the specific container rather than from the Pod overall. Here is a manifest for a Pod that again has just one container:

pods/inject/dapi-volume-resources.yaml

apiVersion: v1
kind: Pod
metadata:
  name: kubernetes-downwardapi-volume-example-2
spec:
  containers:
    - name: client-container
      image: registry.k8s.io/busybox:1.24
      command: ["sh", "-c"]
      args:
      - while true; do
          echo -en '\n';
          if [[ -e /etc/podinfo/cpu_limit ]]; then
            echo -en '\n'; cat /etc/podinfo/cpu_limit; fi;
          if [[ -e /etc/podinfo/cpu_request ]]; then
            echo -en '\n'; cat /etc/podinfo/cpu_request; fi;
          if [[ -e /etc/podinfo/mem_limit ]]; then
            echo -en '\n'; cat /etc/podinfo/mem_limit; fi;
          if [[ -e /etc/podinfo/mem_request ]]; then
            echo -en '\n'; cat /etc/podinfo/mem_request; fi;
          sleep 5;
        done;
      resources:
        requests:
          memory: "32Mi"
          cpu: "125m"
        limits:
          memory: "64Mi"
          cpu: "250m"
      volumeMounts:
        - name: podinfo
          mountPath: /etc/podinfo
  volumes:
    - name: podinfo
      downwardAPI:
        items:
          - path: "cpu_limit"
            resourceFieldRef:
              containerName: client-container
              resource: limits.cpu
              divisor: 1m
          - path: "cpu_request"
            resourceFieldRef:
              containerName: client-container
              resource: requests.cpu
              divisor: 1m
          - path: "mem_limit"
            resourceFieldRef:
              containerName: client-container
              resource: limits.memory
              divisor: 1Mi
          - path: "mem_request"
            resourceFieldRef:
              containerName: client-container
              resource: requests.memory
              divisor: 1Mi

In the manifest, you can see that the Pod has a downwardAPI volume, and that the single container in that Pod mounts the volume at /etc/podinfo.

Look at the items array under downwardAPI. Each element of the array defines a file in the downward API volume.

The first element specifies that in the container named client-container, the value of the limits.cpu field in the format specified by 1m should be published as a file named cpu_limit. The divisor field is optional and has the default value of 1. A divisor of 1 means cores for cpu resources, or bytes for memory resources.

Create the Pod:

kubectl apply -f https://k8s.io/examples/pods/inject/dapi-volume-resources.yaml

Get a shell into the container that is running in your Pod:

kubectl exec -it kubernetes-downwardapi-volume-example-2 -- sh

In your shell, view the cpu_limit file:

# Run this in a shell inside the container
cat /etc/podinfo/cpu_limit

You can use similar commands to view the cpu_request, mem_limit and mem_request files.

Project keys to specific paths and file permissions

You can project keys to specific paths and specific permissions on a per-file basis. For more information, see Secrets.

What's next

Read the spec API definition for Pod. This includes the definition of Container (part of Pod).
Read the list of available fields that you can expose using the downward API.

Read about volumes in the legacy API reference:

Check the Volume API definition which defines a generic volume in a Pod for containers to access.
Check the DownwardAPIVolumeSource API definition which defines a volume that contains Downward API information.
Check the DownwardAPIVolumeFile API definition which contains references to object or resource fields for populating a file in the Downward API volume.
Check the ResourceFieldSelector API definition which specifies the container resources and their output format.

6 - Distribute Credentials Securely Using Secrets

This page shows how to securely inject sensitive data, such as passwords and encryption keys, into Pods.

Before you begin

Convert your secret data to a base-64 representation

Suppose you want to have two pieces of secret data: a username my-app and a password 39528$vdg7Jb. First, use a base64 encoding tool to convert your username and password to a base64 representation. Here's an example using the commonly available base64 program:

echo -n 'my-app' | base64
echo -n '39528$vdg7Jb' | base64

The output shows that the base-64 representation of your username is bXktYXBw, and the base-64 representation of your password is Mzk1MjgkdmRnN0pi.

Caution: Use a local tool trusted by your OS to decrease the security risks of external tools.

Create a Secret

Here is a configuration file you can use to create a Secret that holds your username and password:

pods/inject/secret.yaml

apiVersion: v1
kind: Secret
metadata:
  name: test-secret
data:
  username: bXktYXBw
  password: Mzk1MjgkdmRnN0pi

Create the Secret

kubectl apply -f https://k8s.io/examples/pods/inject/secret.yaml

View information about the Secret:

kubectl get secret test-secret

Output:

NAME          TYPE      DATA      AGE
test-secret   Opaque    2         1m

View more detailed information about the Secret:

kubectl describe secret test-secret

Output:

Name:       test-secret
Namespace:  default
Labels:     <none>
Annotations:    <none>

Type:   Opaque

Data
====
password:   13 bytes
username:   7 bytes

Create a Secret directly with kubectl

If you want to skip the Base64 encoding step, you can create the same Secret using the kubectl create secret command. For example:

kubectl create secret generic test-secret --from-literal='username=my-app' --from-literal='password=39528$vdg7Jb'

This is more convenient. The detailed approach shown earlier runs through each step explicitly to demonstrate what is happening.

Create a Pod that has access to the secret data through a Volume

Here is a configuration file you can use to create a Pod:

pods/inject/secret-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: secret-test-pod
spec:
  containers:
    - name: test-container
      image: nginx
      volumeMounts:
        # name must match the volume name below
        - name: secret-volume
          mountPath: /etc/secret-volume
          readOnly: true
  # The secret data is exposed to Containers in the Pod through a Volume.
  volumes:
    - name: secret-volume
      secret:
        secretName: test-secret

Create the Pod:

kubectl apply -f https://k8s.io/examples/pods/inject/secret-pod.yaml

Verify that your Pod is running:

kubectl get pod secret-test-pod

Output:

NAME              READY     STATUS    RESTARTS   AGE
secret-test-pod   1/1       Running   0          42m

Get a shell into the Container that is running in your Pod:
```
kubectl exec -i -t secret-test-pod -- /bin/bash
```
The secret data is exposed to the Container through a Volume mounted under /etc/secret-volume.
In your shell, list the files in the /etc/secret-volume directory:
```
# Run this in the shell inside the container
ls /etc/secret-volume
```
The output shows two files, one for each piece of secret data:
```
password username
```

In your shell, display the contents of the username and password files:

# Run this in the shell inside the container
echo "$( cat /etc/secret-volume/username )"
echo "$( cat /etc/secret-volume/password )"

The output is your username and password:

my-app
39528$vdg7Jb

Modify your image or command line so that the program looks for files in the mountPath directory. Each key in the Secret data map becomes a file name in this directory.

Project Secret keys to specific file paths

You can also control the paths within the volume where Secret keys are projected. Use the .spec.volumes[].secret.items field to change the target path of each key:

apiVersion: v1
kind: Pod
metadata:
  name: mypod
spec:
  containers:
  - name: mypod
    image: redis
    volumeMounts:
    - name: foo
      mountPath: "/etc/foo"
      readOnly: true
  volumes:
  - name: foo
    secret:
      secretName: mysecret
      items:
      - key: username
        path: my-group/my-username

When you deploy this Pod, the following happens:

The username key from mysecret is available to the container at the path /etc/foo/my-group/my-username instead of at /etc/foo/username.
The password key from that Secret object is not projected.

If you list keys explicitly using .spec.volumes[].secret.items, consider the following:

Only keys specified in items are projected.
To consume all keys from the Secret, all of them must be listed in the items field.
All listed keys must exist in the corresponding Secret. Otherwise, the volume is not created.

Set POSIX permissions for Secret keys

You can set the POSIX file access permission bits for a single Secret key. If you don't specify any permissions, 0644 is used by default. You can also set a default POSIX file mode for the entire Secret volume, and you can override per key if needed.

For example, you can specify a default mode like this:

apiVersion: v1
kind: Pod
metadata:
  name: mypod
spec:
  containers:
  - name: mypod
    image: redis
    volumeMounts:
    - name: foo
      mountPath: "/etc/foo"
  volumes:
  - name: foo
    secret:
      secretName: mysecret
      defaultMode: 0400

The Secret is mounted on /etc/foo; all the files created by the secret volume mount have permission 0400.

Note: If you're defining a Pod or a Pod template using JSON, beware that the JSON specification doesn't support octal literals for numbers because JSON considers 0400 to be the decimal value 400. In JSON, use decimal values for the defaultMode instead. If you're writing YAML, you can write the defaultMode in octal.

Define container environment variables using Secret data

You can consume the data in Secrets as environment variables in your containers.

If a container already consumes a Secret in an environment variable, a Secret update will not be seen by the container unless it is restarted. There are third party solutions for triggering restarts when secrets change.

Define a container environment variable with data from a single Secret

Define an environment variable as a key-value pair in a Secret:

kubectl create secret generic backend-user --from-literal=backend-username='backend-admin'

Assign the backend-username value defined in the Secret to the SECRET_USERNAME environment variable in the Pod specification.

pods/inject/pod-single-secret-env-variable.yaml

apiVersion: v1
kind: Pod
metadata:
  name: env-single-secret
spec:
  containers:
  - name: envars-test-container
    image: nginx
    env:
    - name: SECRET_USERNAME
      valueFrom:
        secretKeyRef:
          name: backend-user
          key: backend-username

Create the Pod:

kubectl create -f https://k8s.io/examples/pods/inject/pod-single-secret-env-variable.yaml

In your shell, display the content of SECRET_USERNAME container environment variable.
```
kubectl exec -i -t env-single-secret -- /bin/sh -c 'echo $SECRET_USERNAME'
```
The output is similar to:
```
backend-admin
```

Define container environment variables with data from multiple Secrets

As with the previous example, create the Secrets first.

kubectl create secret generic backend-user --from-literal=backend-username='backend-admin'
kubectl create secret generic db-user --from-literal=db-username='db-admin'

Define the environment variables in the Pod specification.

pods/inject/pod-multiple-secret-env-variable.yaml

apiVersion: v1
kind: Pod
metadata:
  name: envvars-multiple-secrets
spec:
  containers:
  - name: envars-test-container
    image: nginx
    env:
    - name: BACKEND_USERNAME
      valueFrom:
        secretKeyRef:
          name: backend-user
          key: backend-username
    - name: DB_USERNAME
      valueFrom:
        secretKeyRef:
          name: db-user
          key: db-username

Create the Pod:

kubectl create -f https://k8s.io/examples/pods/inject/pod-multiple-secret-env-variable.yaml

In your shell, display the container environment variables.

kubectl exec -i -t envvars-multiple-secrets -- /bin/sh -c 'env | grep _USERNAME'

The output is similar to:

DB_USERNAME=db-admin
BACKEND_USERNAME=backend-admin

Configure all key-value pairs in a Secret as container environment variables

Note: This functionality is available in Kubernetes v1.6 and later.

Create a Secret containing multiple key-value pairs

kubectl create secret generic test-secret --from-literal=username='my-app' --from-literal=password='39528$vdg7Jb'

Use envFrom to define all of the Secret's data as container environment variables. The key from the Secret becomes the environment variable name in the Pod.

pods/inject/pod-secret-envFrom.yaml

apiVersion: v1
kind: Pod
metadata:
  name: envfrom-secret
spec:
  containers:
  - name: envars-test-container
    image: nginx
    envFrom:
    - secretRef:
        name: test-secret

Create the Pod:

kubectl create -f https://k8s.io/examples/pods/inject/pod-secret-envFrom.yaml

In your shell, display username and password container environment variables.

kubectl exec -i -t envfrom-secret -- /bin/sh -c 'echo "username: $username\npassword: $password\n"'

The output is similar to:

username: my-app
password: 39528$vdg7Jb

Example: Provide prod/test credentials to Pods using Secrets

This example illustrates a Pod which consumes a secret containing production credentials and another Pod which consumes a secret with test environment credentials.

Create a secret for prod environment credentials:

kubectl create secret generic prod-db-secret --from-literal=username=produser --from-literal=password=Y4nys7f11

The output is similar to:

secret "prod-db-secret" created

Create a secret for test environment credentials.
```
kubectl create secret generic test-db-secret --from-literal=username=testuser --from-literal=password=iluvtests
```
The output is similar to:
```
secret "test-db-secret" created
```
Note:
Special characters such as $, \, *, =, and ! will be interpreted by your shell and require escaping.
In most shells, the easiest way to escape the password is to surround it with single quotes ('). For example, if your actual password is S!B\*d$zDsb=, you should execute the command as follows:
```
kubectl create secret generic dev-db-secret --from-literal=username=devuser --from-literal=password='S!B\*d$zDsb='
```
You do not need to escape special characters in passwords from files (--from-file).

Create the Pod manifests:

cat <<EOF > pod.yaml
apiVersion: v1
kind: List
items:
- kind: Pod
  apiVersion: v1
  metadata:
    name: prod-db-client-pod
    labels:
      name: prod-db-client
  spec:
    volumes:
    - name: secret-volume
      secret:
        secretName: prod-db-secret
    containers:
    - name: db-client-container
      image: myClientImage
      volumeMounts:
      - name: secret-volume
        readOnly: true
        mountPath: "/etc/secret-volume"
- kind: Pod
  apiVersion: v1
  metadata:
    name: test-db-client-pod
    labels:
      name: test-db-client
  spec:
    volumes:
    - name: secret-volume
      secret:
        secretName: test-db-secret
    containers:
    - name: db-client-container
      image: myClientImage
      volumeMounts:
      - name: secret-volume
        readOnly: true
        mountPath: "/etc/secret-volume"
EOF

Note: How the specs for the two Pods differ only in one field; this facilitates creating Pods with different capabilities from a common Pod template.

Apply all those objects on the API server by running:
```
kubectl create -f pod.yaml
```

Both containers will have the following files present on their filesystems with the values for each container's environment:

/etc/secret-volume/username
/etc/secret-volume/password

You could further simplify the base Pod specification by using two service accounts:

prod-user with the prod-db-secret
test-user with the test-db-secret

The Pod specification is shortened to:

apiVersion: v1
kind: Pod
metadata:
  name: prod-db-client-pod
  labels:
    name: prod-db-client
spec:
  serviceAccount: prod-db-client
  containers:
  - name: db-client-container
    image: myClientImage

References

What's next

Learn more about Secrets.
Learn about Volumes.