Using Secrets

This topic discusses important properties of secrets and provides an overview on how developers can use them.

The Secret object type provides a mechanism to hold sensitive information such as passwords, OpenShift Container Platform client configuration files, dockercfg files, private source repository credentials, and so on. Secrets decouple sensitive content from the pods. You can mount secrets into containers using a volume plug-in or the system can use secrets to perform actions on behalf of a pod.

apiVersion: "v1"
kind: "Secret"
metadata:
  name: "mysecret"
namespace: "myns"
data: (1)
  username: "dmFsdWUtMQ0K"
  password: "dmFsdWUtMg0KDQo="
1 The allowable format for the keys in the data field must meet the guidelines in the DNS_SUBDOMAIN value in the Kubernetes identifiers glossary.

Properties of Secrets

Key properties include:

  • Secret data can be referenced independently from its definition.

  • Secret data volumes are backed by temporary file-storage facilities (tmpfs) and never come to rest on a node.

  • Secret data can be shared within a namespace.

Creating Secrets

You must create a secret before creating the pods that depend on that secret.

When creating secrets:

  • Create a secret object with secret data.

  • Update the pod’s service account to allow the reference to the secret.

  • Create a pod, which consumes the secret as an environment variable or as a file (using a secret volume).

To create a secret object, use the following command, where the JSON file is a predefined secret:

$ oc create -f secret.json

Updating Secrets

When you modify the value of a secret, the value (used by an already running pod) will not dynamically change. To change a secret, you must delete the original pod and create a new pod (perhaps with an identical PodSpec).

Updating a secret follows the same workflow as deploying a new container image. You can use the kubectl rolling-update command.

The resourceVersion value in a secret is not specified when it is referenced. Therefore, if a secret is updated at the same time as pods are starting, then the version of the secret will be used for the pod will not be defined.

Currently, it is not possible to check the resource version of a secret object that was used when a pod was created. It is planned that pods will report this information, so that a controller could restart ones using a old resourceVersion. In the interim, do not update the data of existing secrets, but create new ones with distinct names.

Secrets in Volumes and Environment Variables

See examples of YAML files with secret data.

After you create a secret, you can:

  1. Create the pod to reference your secret:

    $ oc create -f <your_yaml_file>.yaml
  2. Get the logs:

    $ oc logs secret-example-pod
  3. Delete the pod:

    $ oc delete pod secret-example-pod

Image Pull Secrets

See Using Image Pull Secrets for more information.

Source Clone Secrets

See Source Secrets for more information.

Service Serving Certificate Secrets

This feature is currently in Technology Preview.

To secure communication to your service, have the cluster generate a signed serving certificate/key pair into a secret in your namespace. To do this, set the service.alpha.openshift.io/serving-cert-secret-name to the name you want to use for your secret. Then, your PodSpec can mount that secret. When it is available, your pod will run. The certificate will be good for the internal service DNS name, <service.name>.<service.namespace>.svc. The certificate and key are in PEM format, stored in tls.crt and tls.key respectively. They are regenerated upon expiration. View the expiration date in the service.alpha.openshift.io/expiry annotation on the secret, which is in RFC3339 format.

In most cases, the service DNS name <service.name>.<service.namespace>.svc is not externally routable. The primary use of <service.name>.<service.namespace>.svc is for intracluster or intraservice communication, and with re-encrypt routes.

Other pods can trust cluster-created certificates (which are only signed for internal DNS names), by using the CA bundle in the /var/run/secrets/kubernetes.io/serviceaccount/service-ca.crt file that is automatically mounted in their pod.

Restrictions

To use a secret, a pod needs to reference the secret. A secret can be used with a pod in three ways: - to populate environment variables for containers. - as files in a volume mounted on one or more of its containers. - by kubelet when pulling images for the pod.

Volume type secrets write data into the container as a file using the volume mechanism. imagePullSecrets use service accounts for the automatic injection of the secret into all pods in a namespaces.

When a template contains a secret definition, the only way for the template to use the provided secret is to ensure that the secret volume sources are validated and that the specified object reference actually points to an object of type Secret. Therefore, a secret needs to be created before any pods that depend on it. The most effective way to ensure this is to have it get injected automatically through the use of a service account.

Secret API objects reside in a namespace. They can only be referenced by pods in that same namespace.

Individual secrets are limited to 1MB in size. This is to discourage the creation of large secrets that would exhaust apiserver and kubelet memory. However, creation of a number of smaller secrets could also exhaust memory.

Secret Data Keys

Secret keys must be in a DNS subdomain.

Examples

Example 1. YAML of a Pod Populating Files in a Volume with Secret Data
apiVersion: v1
kind: Pod
metadata:
  name: secret-example-pod
spec:
  containers:
    - name: secret-test-container
      image: busybox
      command: [ "/bin/sh", "-c", "cat /etc/secret-volume/*" ]
      volumeMounts:
          # name must match the volume name below
          - name: secret-volume
            mountPath: /etc/secret-volume
            readOnly: true
  volumes:
    - name: secret-volume
      secret:
        secretName: test-secret
  restartPolicy: Never
Example 2. YAML of a Pod Populating Environment Variables with Secret Data
apiVersion: v1
kind: Pod
metadata:
  name: secret-example-pod
spec:
  containers:
    - name: secret-test-container
      image: busybox
      command: [ "/bin/sh", "-c", "export" ]
      env:
        - name: TEST_SECRET_USERNAME_ENV_VAR
          valueFrom:
            secretKeyRef:
              name: test-secret
              key: username
  restartPolicy: Never