Objects of type
secret are intended to hold sensitive information, such as
passwords, OAuth tokens, and ssh keys. Putting this information in a
is safer and more flexible than putting it verbatim in a
pod definition or in
a docker image. See Secrets design document for more information.
A Secret is an object that contains a small amount of sensitive data such as a password, a token, or a key. Such information might otherwise be put in a Pod specification or in an image; putting it in a Secret object allows for more control over how it is used, and reduces the risk of accidental exposure.
Users can create secrets, and the system also creates some secrets.
To use a secret, a pod needs to reference the secret. A secret can be used with a pod in two ways: as files in a volume mounted on one or more of its containers, or used by kubelet when pulling images for the pod.
Kubernetes automatically creates secrets which contain credentials for accessing the API and it automatically modifies your pods to use this type of secret.
The automatic creation and use of API credentials can be disabled or overridden if desired. However, if all you need to do is securely access the apiserver, this is the recommended workflow.
See the Service Account documentation for more information on how Service Accounts work.
Say that some pods need to access a database. The
username and password that the pods should use is in the files
./password.txt on your local machine.
# Create files needed for rest of example. $ echo -n "admin" > ./username.txt $ echo -n "1f2d1e2e67df" > ./password.txt
kubectl create secret command
packages these files into a Secret and creates
the object on the Apiserver.
$ kubectl create secret generic db-user-pass --from-file=./username.txt --from-file=./password.txt secret "db-user-pass" created
You can check that the secret was created like this:
$ kubectl get secrets NAME TYPE DATA AGE db-user-pass Opaque 2 51s $ kubectl describe secrets/db-user-pass Name: db-user-pass Namespace: default Labels: <none> Annotations: <none> Type: Opaque Data ==== password.txt: 12 bytes username.txt: 5 bytes
Note that neither
describe shows the contents of the file by default.
This is to protect the secret from being exposed accidentally to someone looking
or from being stored in a terminal log.
See decoding a secret for how to see the contents.
You can also create a secret object in a file first, in json or yaml format, and then create that object.
Each item must be base64 encoded:
$ echo -n "admin" | base64 YWRtaW4= $ echo -n "1f2d1e2e67df" | base64 MWYyZDFlMmU2N2Rm
Now write a secret object that looks like this:
apiVersion: v1 kind: Secret metadata: name: mysecret type: Opaque data: username: YWRtaW4= password: MWYyZDFlMmU2N2Rm
The data field is a map. Its keys must match
DNS_SUBDOMAIN, except that leading dots are also
allowed. The values are arbitrary data, encoded using base64.
Create the secret using
$ kubectl create -f ./secret.yaml secret "mysecret" created
Encoding Note: The serialized JSON and YAML values of secret data are
encoded as base64 strings. Newlines are not valid within these strings and must
be omitted. When using the
base64 utility on Darwin/OS X users should avoid
-b option to split long lines. Conversely Linux users should add
-w 0 to
base64 commands or the pipeline
base64 | tr -d '\n' if
-w option is not available.
Secrets can be retrieved via the
kubectl get secret command. For example, to retrieve the secret created in the previous section:
$ kubectl get secret mysecret -o yaml apiVersion: v1 data: username: YWRtaW4= password: MWYyZDFlMmU2N2Rm kind: Secret metadata: creationTimestamp: 2016-01-22T18:41:56Z name: mysecret namespace: default resourceVersion: "164619" selfLink: /api/v1/namespaces/default/secrets/mysecret uid: cfee02d6-c137-11e5-8d73-42010af00002 type: Opaque
Decode the password field:
$ echo "MWYyZDFlMmU2N2Rm" | base64 --decode 1f2d1e2e67df
Secrets can be mounted as data volumes or be exposed as environment variables to be used by a container in a pod. They can also be used by other parts of the system, without being directly exposed to the pod. For example, they can hold credentials that other parts of the system should use to interact with external systems on your behalf.
To consume a Secret in a volume in a Pod:
spec.volumes. Name the volume anything, and have a
spec.volumes.secret.secretNamefield equal to the name of the secret object.
spec.containers.volumeMountsto each container that needs the secret. Specify
spec.containers.volumeMounts.readOnly = trueand
spec.containers.volumeMounts.mountPathto an unused directory name where you would like the secrets to appear.
datamap becomes the filename under
This is an example of a pod that mounts a secret in a volume:
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
Each secret you want to use needs to be referred to in
If there are multiple containers in the pod, then each container needs its
volumeMounts block, but only one
spec.volumes is needed per secret.
You can package many files into one secret, or use many secrets, whichever is convenient.
Projection of secret keys to specific paths
We can also control the paths within the volume where Secret keys are projected.
You can use
spec.volumes.secret.items field to change 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
What will happen:
usernamesecret is stored under
/etc/foo/my-group/my-usernamefile instead of
passwordsecret is not projected
spec.volumes.secret.items is used, only keys specified in
items are projected.
To consume all keys from the secret, all of them must be listed in the
All listed keys must exist in the corresponding secret. Otherwise, the volume is not created.
Secret files permissions
You can also specify the permission mode bits files part of a secret will have.
If you don’t specify any,
0644 is used by default. You can specify a default
mode for the whole secret volume and 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: 256
Then, the secret will be mounted on
/etc/foo and all the files created by the
secret volume mount will have permission
Note that the JSON spec doesn’t support octal notation, so use the value 256 for 0400 permissions. If you use yaml instead of json for the pod, you can use octal notation to specify permissions in a more natural way.
You can also use mapping, as in the previous example, and specify different permission for different files 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 items: - key: username path: my-group/my-username mode: 511
In this case, the file resulting in
/etc/foo/my-group/my-username will have
permission value of
0777. Owing to JSON limitations, you must specify the mode
in decimal notation.
Note that this permission value might be displayed in decimal notation if you read it later.
Consuming Secret Values from Volumes
Inside the container that mounts a secret volume, the secret keys appear as files and the secret values are base-64 decoded and stored inside these files. This is the result of commands executed inside the container from the example above:
$ ls /etc/foo/ username password $ cat /etc/foo/username admin $ cat /etc/foo/password 1f2d1e2e67df
The program in a container is responsible for reading the secrets from the files.
Mounted Secrets are updated automatically
When a secret being already consumed in a volume is updated, projected keys are eventually updated as well. Kubelet is checking whether the mounted secret is fresh on every periodic sync. However, it is using its local ttl-based cache for getting the current value of the secret. As a result, the total delay from the moment when the secret is updated to the moment when new keys are projected to the pod can be as long as kubelet sync period + ttl of secrets cache in kubelet.
To use a secret in an environment variable in a pod:
This is an example of a pod that uses secrets from environment variables:
apiVersion: v1 kind: Pod metadata: name: secret-env-pod spec: containers: - name: mycontainer image: redis env: - name: SECRET_USERNAME valueFrom: secretKeyRef: name: mysecret key: username - name: SECRET_PASSWORD valueFrom: secretKeyRef: name: mysecret key: password restartPolicy: Never
Consuming Secret Values from Environment Variables
Inside a container that consumes a secret in an environment variables, the secret keys appear as normal environment variables containing the base-64 decoded values of the secret data. This is the result of commands executed inside the container from the example above:
$ echo $SECRET_USERNAME admin $ echo $SECRET_PASSWORD 1f2d1e2e67df
An imagePullSecret is a way to pass a secret that contains a Docker (or other) image registry password to the Kubelet so it can pull a private image on behalf of your Pod.
Manually specifying an imagePullSecret
Use of imagePullSecrets is described in the images documentation
You can manually create an imagePullSecret, and reference it from a serviceAccount. Any pods created with that serviceAccount or that default to use that serviceAccount, will get their imagePullSecret field set to that of the service account. See Adding ImagePullSecrets to a service account for a detailed explanation of that process.
Manually created secrets (e.g. one containing a token for accessing a github account) can be automatically attached to pods based on their service account. See Injecting Information into Pods Using a PodPreset for a detailed explanation of that process.
Secret volume sources are validated to ensure 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.
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 creation of very large secrets which would exhaust apiserver and kubelet memory. However, creation of many smaller secrets could also exhaust memory. More comprehensive limits on memory usage due to secrets is a planned feature.
Kubelet only supports use of secrets for Pods it gets from the API server.
This includes any pods created using kubectl, or indirectly via a replication
controller. It does not include pods created via the kubelets
--manifest-url flag, its
--config flag, or its REST API (these are
not common ways to create pods.)
Secrets must be created before they are consumed in pods as environment variables unless they are marked as optional. References to Secrets that do not exist will prevent the pod from starting.
secretKeyRef to keys that do not exist in a named Secret
will prevent the pod from starting.
Secrets used to populate environment variables via
envFrom that have keys
that are considered invalid environment variable names will have those keys
skipped. The pod will be allowed to start. There will be an event whose
InvalidVariableNames and the message will contain the list of
invalid keys that were skipped. The example shows a pod which refers to the
default/mysecret ConfigMap that contains 2 invalid keys, 1badkey and 2alsobad.
$ kubectl get events LASTSEEN FIRSTSEEN COUNT NAME KIND SUBOBJECT TYPE REASON 0s 0s 1 dapi-test-pod Pod Warning InvalidEnvironmentVariableNames kubelet, 127.0.0.1 Keys [1badkey, 2alsobad] from the EnvFrom secret default/mysecret were skipped since they are considered invalid environment variable names.
When a pod is created via the API, there is no check whether a referenced secret exists. Once a pod is scheduled, the kubelet will try to fetch the secret value. If the secret cannot be fetched because it does not exist or because of a temporary lack of connection to the API server, kubelet will periodically retry. It will report an event about the pod explaining the reason it is not started yet. Once the secret is fetched, the kubelet will create and mount a volume containing it. None of the pod’s containers will start until all the pod’s volumes are mounted.
Create a secret containing some ssh keys:
$ kubectl create secret generic ssh-key-secret --from-file=ssh-privatekey=/path/to/.ssh/id_rsa --from-file=ssh-publickey=/path/to/.ssh/id_rsa.pub
Security Note: think carefully before sending your own ssh keys: other users of the cluster may have access to the secret. Use a service account which you want to be accessible to all the users with whom you share the Kubernetes cluster, and can revoke if they are compromised.
Now we can create a pod which references the secret with the ssh key and consumes it in a volume:
kind: Pod apiVersion: v1 metadata: name: secret-test-pod labels: name: secret-test spec: volumes: - name: secret-volume secret: secretName: ssh-key-secret containers: - name: ssh-test-container image: mySshImage volumeMounts: - name: secret-volume readOnly: true mountPath: "/etc/secret-volume"
When the container’s command runs, the pieces of the key will be available in:
The container is then free to use the secret data to establish an ssh connection.
This example illustrates a pod which consumes a secret containing prod credentials and another pod which consumes a secret with test environment credentials.
Make the secrets:
$ kubectl create secret generic prod-db-secret --from-literal=username=produser --from-literal=password=Y4nys7f11 secret "prod-db-secret" created $ kubectl create secret generic test-db-secret --from-literal=username=testuser --from-literal=password=iluvtests secret "test-db-secret" created
Now make the pods:
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"
Both containers will have the following files present on their filesystems with the values for each container’s environment:
Note how the specs for the two pods differ only in one field; this facilitates creating pods with different capabilities from a common pod config template.
You could further simplify the base pod specification by using two Service Accounts:
one called, say,
prod-user with the
prod-db-secret, and one called, say,
test-user with the
test-db-secret. Then, the pod spec can be shortened to, for example:
kind: Pod apiVersion: v1 metadata: name: prod-db-client-pod labels: name: prod-db-client spec: serviceAccount: prod-db-client containers: - name: db-client-container image: myClientImage
In order to make piece of data ‘hidden’ (i.e., in a file whose name begins with a dot character), simply make that key begin with a dot. For example, when the following secret is mounted into a volume:
kind: Secret apiVersion: v1 metadata: name: dotfile-secret data: .secret-file: dmFsdWUtMg0KDQo= --- kind: Pod apiVersion: v1 metadata: name: secret-dotfiles-pod spec: volumes: - name: secret-volume secret: secretName: dotfile-secret containers: - name: dotfile-test-container image: gcr.io/google_containers/busybox command: - ls - "-l" - "/etc/secret-volume" volumeMounts: - name: secret-volume readOnly: true mountPath: "/etc/secret-volume"
secret-volume will contain a single file, called
dotfile-test-container will have this file present at the path
Files beginning with dot characters are hidden from the output of
you must use
ls -la to see them when listing directory contents.
Consider a program that needs to handle HTTP requests, do some complex business logic, and then sign some messages with an HMAC. Because it has complex application logic, there might be an unnoticed remote file reading exploit in the server, which could expose the private key to an attacker.
This could be divided into two processes in two containers: a frontend container which handles user interaction and business logic, but which cannot see the private key; and a signer container that can see the private key, and responds to simple signing requests from the frontend (e.g. over localhost networking).
With this partitioned approach, an attacker now has to trick the application server into doing something rather arbitrary, which may be harder than getting it to read a file.
Secrets often hold values that span a spectrum of importance, many of which can cause escalations within Kubernetes (e.g. service account tokens) and to external systems. Even if an individual app can reason about the power of the secrets it expects to interact with, other apps within the same namespace can render those assumptions invalid.
For these reasons
list requests for secrets within a namespace are
extremely powerful capabilities and should be avoided, since listing secrets allows
the clients to inspect the values if all secrets are in that namespace. The ability to
list all secrets in a cluster should be reserved for only the most
privileged, system-level components.
Applications that need to access the secrets API should perform
get requests on
the secrets they need. This lets administrators restrict access to all secrets
while white-listing access to individual instances that
the app needs.
For improved performance over a looping
get, clients can design resources that
reference a secret then
watch the resource, re-requesting the secret when the
reference changes. Additionally, a “bulk watch” API
to let clients
watch individual resources has also been proposed, and will likely
be available in future releases of Kubernetes.
secret objects can be created independently of the
pods that use
them, there is less risk of the secret being exposed during the workflow of
creating, viewing, and editing pods. The system can also take additional
secret objects, such as avoiding writing them to disk where
A secret is only sent to a node if a pod on that node requires it. It is not written to disk. It is stored in a tmpfs. It is deleted once the pod that depends on it is deleted.
On most Kubernetes-project-maintained distributions, communication between user to the apiserver, and from apiserver to the kubelets, is protected by SSL/TLS. Secrets are protected when transmitted over these channels.
Secret data on nodes is stored in tmpfs volumes and thus does not come to rest on the node.
There may be secrets for several pods on the same node. However, only the secrets that a pod requests are potentially visible within its containers. Therefore, one Pod does not have access to the secrets of another pod.
There may be several containers in a pod. However, each container in a pod has
to request the secret volume in its
volumeMounts for it to be visible within
the container. This can be used to construct useful security partitions at the