Objects of type `secret` are intended to hold sensitive information, such as
passwords, OAuth tokens, and ssh keys. Putting this information in a `secret`
is safer and more flexible than putting it verbatim in a `pod` definition or in
a docker image. See [Secrets design document](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/docs/design/secrets.md) for more information.
* TOC
{:toc}
## Overview of Secrets
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](/docs/concepts/storage/volumes/) mounted on one or more of
its containers, or used by kubelet when pulling images for the pod.
### Built-in Secrets
#### Service Accounts Automatically Create and Attach Secrets with API Credentials
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](/docs/user-guide/service-accounts) documentation for more
information on how Service Accounts work.
### Creating your own Secrets
#### Creating a Secret Using kubectl create secret
Say that some pods need to access a database. The
username and password that the pods should use is in the files
`./username.txt` and `./password.txt` on your local machine.
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.
#### Using Secrets as Files from a Pod
To consume a Secret in a volume in a Pod:
1. Create a secret or use an existing one. Multiple pods can reference the same secret.
1. Modify your Pod definition to add a volume under `spec.volumes[]`. Name the volume anything, and have a `spec.volumes[].secret.secretName` field equal to the name of the secret object.
1. Add a `spec.containers[].volumeMounts[]` to each container that needs the secret. Specify `spec.containers[].volumeMounts[].readOnly = true` and `spec.containers[].volumeMounts[].mountPath` to an unused directory name where you would like the secrets to appear.
1. Modify your image and/or command line so that the program looks for files in that directory. Each key in the secret `data` map becomes the filename under `mountPath`.
This is an example of a pod that mounts a secret in a volume:
```json
{
"apiVersion": "v1",
"kind": "Pod",
"metadata": {
"name": "mypod",
"namespace": "myns"
},
"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 `spec.volumes`.
If there are multiple containers in the pod, then each container needs its
own `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:
```json
{
"apiVersion": "v1",
"kind": "Pod",
"metadata": {
"name": "mypod",
"namespace": "myns"
},
"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:
*`username` secret is stored under `/etc/foo/my-group/my-username` file instead of `/etc/foo/username`.
*`password` secret is not projected
If `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 `items` field.
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:
```json
{
"apiVersion": "v1",
"kind": "Pod",
"metadata": {
"name": "mypod",
"namespace": "myns"
},
"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 `0400`.
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:
```json
{
"apiVersion": "v1",
"kind": "Pod",
"metadata": {
"name": "mypod",
"namespace": "myns"
},
"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:
```shell
$ 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.
#### Using Secrets as Environment Variables
To use a secret in an environment variable in a pod:
1. Create a secret or use an existing one. Multiple pods can reference the same secret.
1. Modify your Pod definition in each container that you wish to consume the value of a secret key to add an environment variable for each secret key you wish to consume. The environment variable that consumes the secret key should populate the secret's name and key in `env[x].valueFrom.secretKeyRef`.
1. Modify your image and/or command line so that the program looks for values in the specified environment variables
This is an example of a pod that uses secrets from environment variables:
```yaml
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:
```shell
$ echo $SECRET_USERNAME
admin
$ echo $SECRET_PASSWORD
1f2d1e2e67df
```
#### Using imagePullSecrets
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](/docs/concepts/containers/images/#specifying-imagepullsecrets-on-a-pod)
### Arranging for imagePullSecrets to be Automatically Attached
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 [here](/docs/user-guide/service-accounts/#adding-imagepullsecrets-to-a-service-account)
for a detailed explanation of that process.
#### Automatic Mounting of Manually Created Secrets
We plan to extend the service account behavior so that 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.
*This is not implemented yet. See [issue 9902](http://issue.k8s.io/9902).*
## Details
### Restrictions
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
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.
References via `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
reason is `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.
```shell
$ kubectl.sh 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.
**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 have 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:
```json
{
"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:
```shell
/etc/secret-volume/ssh-publickey
/etc/secret-volume/ssh-privatekey
```
The container is then free to use the secret data to establish an ssh connection.
### Use-Case: Pods with prod / test credentials
This example illustrates a pod which consumes a secret containing prod
credentials and another pod which consumes a secret with test environment
