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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 a container image. Using a Secret means that you don't need to include confidential data in your application code.
Because Secrets can be created independently of the Pods that use them, there is less risk of the Secret (and its data) being exposed during the workflow of creating, viewing, and editing Pods. Kubernetes, and applications that run in your cluster, can also take additional precautions with Secrets, such as avoiding writing confidential data to nonvolatile storage.
Secrets are similar to ConfigMaps but are specifically intended to hold confidential data.
Kubernetes Secrets are, by default, stored unencrypted in the API server's underlying data store (etcd). Anyone with API access can retrieve or modify a Secret, and so can anyone with access to etcd. Additionally, anyone who is authorized to create a Pod in a namespace can use that access to read any Secret in that namespace; this includes indirect access such as the ability to create a Deployment.
In order to safely use Secrets, take at least the following steps:
- Enable Encryption at Rest for Secrets.
- Enable or configure RBAC rules that restrict reading data in Secrets (including via indirect means).
- Where appropriate, also use mechanisms such as RBAC to limit which principals are allowed to create new Secrets or replace existing ones.
Overview of Secrets
To use a Secret, a Pod needs to reference the Secret. A Secret can be used with a Pod in three ways:
- As files in a volume mounted on one or more of its containers.
- As container environment variable.
- By the kubelet when pulling images for the Pod.
The Kubernetes control plane also uses Secrets; for example, bootstrap token Secrets are a mechanism to help automate node registration.
The name of a Secret object must be a valid
DNS subdomain name.
You can specify the data
and/or the stringData
field when creating a
configuration file for a Secret. The data
and the stringData
fields are optional.
The values for all keys in the data
field have to be base64-encoded strings.
If the conversion to base64 string is not desirable, you can choose to specify
the stringData
field instead, which accepts arbitrary strings as values.
The keys of data
and stringData
must consist of alphanumeric characters,
-
, _
or .
. All key-value pairs in the stringData
field are internally
merged into the data
field. If a key appears in both the data
and the
stringData
field, the value specified in the stringData
field takes
precedence.
Types of Secret
When creating a Secret, you can specify its type using the type
field of
a Secret resource, or certain equivalent kubectl
command line flags (if available).
The type
of a Secret is used to facilitate programmatic handling of different
kinds of confidential data.
Kubernetes provides several builtin types for some common usage scenarios. These types vary in terms of the validations performed and the constraints Kubernetes imposes on them.
Builtin Type | Usage |
---|---|
Opaque |
arbitrary user-defined data |
kubernetes.io/service-account-token |
service account token |
kubernetes.io/dockercfg |
serialized ~/.dockercfg file |
kubernetes.io/dockerconfigjson |
serialized ~/.docker/config.json file |
kubernetes.io/basic-auth |
credentials for basic authentication |
kubernetes.io/ssh-auth |
credentials for SSH authentication |
kubernetes.io/tls |
data for a TLS client or server |
bootstrap.kubernetes.io/token |
bootstrap token data |
You can define and use your own Secret type by assigning a non-empty string as the
type
value for a Secret object. An empty string is treated as an Opaque
type.
Kubernetes doesn't impose any constraints on the type name. However, if you
are using one of the builtin types, you must meet all the requirements defined
for that type.
Opaque secrets
Opaque
is the default Secret type if omitted from a Secret configuration file.
When you create a Secret using kubectl
, you will use the generic
subcommand to indicate an Opaque
Secret type. For example, the following
command creates an empty Secret of type Opaque
.
kubectl create secret generic empty-secret
kubectl get secret empty-secret
The output looks like:
NAME TYPE DATA AGE
empty-secret Opaque 0 2m6s
The DATA
column shows the number of data items stored in the Secret.
In this case, 0
means we have created an empty Secret.
Service account token Secrets
A kubernetes.io/service-account-token
type of Secret is used to store a
token that identifies a service account. When using this Secret type, you need
to ensure that the kubernetes.io/service-account.name
annotation is set to an
existing service account name. A Kubernetes controller fills in some other
fields such as the kubernetes.io/service-account.uid
annotation and the
token
key in the data
field set to actual token content.
The following example configuration declares a service account token Secret:
apiVersion: v1
kind: Secret
metadata:
name: secret-sa-sample
annotations:
kubernetes.io/service-account.name: "sa-name"
type: kubernetes.io/service-account-token
data:
# You can include additional key value pairs as you do with Opaque Secrets
extra: YmFyCg==
When creating a Pod
, Kubernetes automatically creates a service account Secret
and automatically modifies your Pod to use this Secret. The service account token
Secret contains credentials for accessing the API.
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 API server, this is the recommended workflow.
See the ServiceAccount
documentation for more information on how service accounts work.
You can also check the automountServiceAccountToken
field and the
serviceAccountName
field of the
Pod
for information on referencing service account from Pods.
Docker config Secrets
You can use one of the following type
values to create a Secret to
store the credentials for accessing a Docker registry for images.
kubernetes.io/dockercfg
kubernetes.io/dockerconfigjson
The kubernetes.io/dockercfg
type is reserved to store a serialized
~/.dockercfg
which is the legacy format for configuring Docker command line.
When using this Secret type, you have to ensure the Secret data
field
contains a .dockercfg
key whose value is content of a ~/.dockercfg
file
encoded in the base64 format.
The kubernetes.io/dockerconfigjson
type is designed for storing a serialized
JSON that follows the same format rules as the ~/.docker/config.json
file
which is a new format for ~/.dockercfg
.
When using this Secret type, the data
field of the Secret object must
contain a .dockerconfigjson
key, in which the content for the
~/.docker/config.json
file is provided as a base64 encoded string.
Below is an example for a kubernetes.io/dockercfg
type of Secret:
apiVersion: v1
kind: Secret
metadata:
name: secret-dockercfg
type: kubernetes.io/dockercfg
data:
.dockercfg: |
"<base64 encoded ~/.dockercfg file>"
stringData
field instead.
When you create these types of Secrets using a manifest, the API
server checks whether the expected key does exists in the data
field, and
it verifies if the value provided can be parsed as a valid JSON. The API
server doesn't validate if the JSON actually is a Docker config file.
When you do not have a Docker config file, or you want to use kubectl
to create a Docker registry Secret, you can do:
kubectl create secret docker-registry secret-tiger-docker \
--docker-username=tiger \
--docker-password=pass113 \
--docker-email=tiger@acme.com \
--docker-server=my-registry.example:5000
This command creates a Secret of type kubernetes.io/dockerconfigjson
.
If you dump the .dockerconfigjson
content from the data
field, you will
get the following JSON content which is a valid Docker configuration created
on the fly:
{
"apiVersion": "v1",
"data": {
".dockerconfigjson": "eyJhdXRocyI6eyJteS1yZWdpc3RyeTo1MDAwIjp7InVzZXJuYW1lIjoidGlnZXIiLCJwYXNzd29yZCI6InBhc3MxMTMiLCJlbWFpbCI6InRpZ2VyQGFjbWUuY29tIiwiYXV0aCI6ImRHbG5aWEk2Y0dGemN6RXhNdz09In19fQ=="
},
"kind": "Secret",
"metadata": {
"creationTimestamp": "2021-07-01T07:30:59Z",
"name": "secret-tiger-docker",
"namespace": "default",
"resourceVersion": "566718",
"uid": "e15c1d7b-9071-4100-8681-f3a7a2ce89ca"
},
"type": "kubernetes.io/dockerconfigjson"
}
Basic authentication Secret
The kubernetes.io/basic-auth
type is provided for storing credentials needed
for basic authentication. When using this Secret type, the data
field of the
Secret must contain one of the following two keys:
username
: the user name for authentication;password
: the password or token for authentication.
Both values for the above two keys are base64 encoded strings. You can, of
course, provide the clear text content using the stringData
for Secret
creation.
The following YAML is an example config for a basic authentication Secret:
apiVersion: v1
kind: Secret
metadata:
name: secret-basic-auth
type: kubernetes.io/basic-auth
stringData:
username: admin
password: t0p-Secret
The basic authentication Secret type is provided only for user's convenience.
You can create an Opaque
for credentials used for basic authentication.
However, using the builtin Secret type helps unify the formats of your credentials
and the API server does verify if the required keys are provided in a Secret
configuration.
SSH authentication secrets
The builtin type kubernetes.io/ssh-auth
is provided for storing data used in
SSH authentication. When using this Secret type, you will have to specify a
ssh-privatekey
key-value pair in the data
(or stringData
) field
as the SSH credential to use.
The following YAML is an example config for a SSH authentication Secret:
apiVersion: v1
kind: Secret
metadata:
name: secret-ssh-auth
type: kubernetes.io/ssh-auth
data:
# the data is abbreviated in this example
ssh-privatekey: |
MIIEpQIBAAKCAQEAulqb/Y ...
The SSH authentication Secret type is provided only for user's convenience.
You can create an Opaque
for credentials used for SSH authentication.
However, using the builtin Secret type helps unify the formats of your credentials
and the API server does verify if the required keys are provided in a Secret
configuration.
known_hosts
file added to a
ConfigMap.
TLS secrets
Kubernetes provides a builtin Secret type kubernetes.io/tls
for storing
a certificate and its associated key that are typically used for TLS . This
data is primarily used with TLS termination of the Ingress resource, but may
be used with other resources or directly by a workload.
When using this type of Secret, the tls.key
and the tls.crt
key must be provided
in the data
(or stringData
) field of the Secret configuration, although the API
server doesn't actually validate the values for each key.
The following YAML contains an example config for a TLS Secret:
apiVersion: v1
kind: Secret
metadata:
name: secret-tls
type: kubernetes.io/tls
data:
# the data is abbreviated in this example
tls.crt: |
MIIC2DCCAcCgAwIBAgIBATANBgkqh ...
tls.key: |
MIIEpgIBAAKCAQEA7yn3bRHQ5FHMQ ...
The TLS Secret type is provided for user's convenience. You can create an Opaque
for credentials used for TLS server and/or client. However, using the builtin Secret
type helps ensure the consistency of Secret format in your project; the API server
does verify if the required keys are provided in a Secret configuration.
When creating a TLS Secret using kubectl
, you can use the tls
subcommand
as shown in the following example:
kubectl create secret tls my-tls-secret \
--cert=path/to/cert/file \
--key=path/to/key/file
The public/private key pair must exist beforehand. The public key certificate
for --cert
must be .PEM encoded (Base64-encoded DER format), and match the
given private key for --key
.
The private key must be in what is commonly called PEM private key format,
unencrypted. In both cases, the initial and the last lines from PEM (for
example, --------BEGIN CERTIFICATE-----
and -------END CERTIFICATE----
for
a certificate) are not included.
Bootstrap token Secrets
A bootstrap token Secret can be created by explicitly specifying the Secret
type
to bootstrap.kubernetes.io/token
. This type of Secret is designed for
tokens used during the node bootstrap process. It stores tokens used to sign
well known ConfigMaps.
A bootstrap token Secret is usually created in the kube-system
namespace and
named in the form bootstrap-token-<token-id>
where <token-id>
is a 6 character
string of the token ID.
As a Kubernetes manifest, a bootstrap token Secret might look like the following:
apiVersion: v1
kind: Secret
metadata:
name: bootstrap-token-5emitj
namespace: kube-system
type: bootstrap.kubernetes.io/token
data:
auth-extra-groups: c3lzdGVtOmJvb3RzdHJhcHBlcnM6a3ViZWFkbTpkZWZhdWx0LW5vZGUtdG9rZW4=
expiration: MjAyMC0wOS0xM1QwNDozOToxMFo=
token-id: NWVtaXRq
token-secret: a3E0Z2lodnN6emduMXAwcg==
usage-bootstrap-authentication: dHJ1ZQ==
usage-bootstrap-signing: dHJ1ZQ==
A bootstrap type Secret has the following keys specified under data
:
token-id
: A random 6 character string as the token identifier. Required.token-secret
: A random 16 character string as the actual token secret. Required.description
: A human-readable string that describes what the token is used for. Optional.expiration
: An absolute UTC time using RFC3339 specifying when the token should be expired. Optional.usage-bootstrap-<usage>
: A boolean flag indicating additional usage for the bootstrap token.auth-extra-groups
: A comma-separated list of group names that will be authenticated as in addition to thesystem:bootstrappers
group.
The above YAML may look confusing because the values are all in base64 encoded strings. In fact, you can create an identical Secret using the following YAML:
apiVersion: v1
kind: Secret
metadata:
# Note how the Secret is named
name: bootstrap-token-5emitj
# A bootstrap token Secret usually resides in the kube-system namespace
namespace: kube-system
type: bootstrap.kubernetes.io/token
stringData:
auth-extra-groups: "system:bootstrappers:kubeadm:default-node-token"
expiration: "2020-09-13T04:39:10Z"
# This token ID is used in the name
token-id: "5emitj"
token-secret: "kq4gihvszzgn1p0r"
# This token can be used for authentication
usage-bootstrap-authentication: "true"
# and it can be used for signing
usage-bootstrap-signing: "true"
Creating a Secret
There are several options to create a Secret:
Editing a Secret
An existing Secret may be edited with the following command:
kubectl edit secrets mysecret
This will open the default configured editor and allow for updating the base64 encoded Secret values in the data
field:
# Please edit the object below. Lines beginning with a '#' will be ignored,
# and an empty file will abort the edit. If an error occurs while saving this file will be
# reopened with the relevant failures.
#
apiVersion: v1
data:
username: YWRtaW4=
password: MWYyZDFlMmU2N2Rm
kind: Secret
metadata:
annotations:
kubectl.kubernetes.io/last-applied-configuration: { ... }
creationTimestamp: 2016-01-22T18:41:56Z
name: mysecret
namespace: default
resourceVersion: "164619"
uid: cfee02d6-c137-11e5-8d73-42010af00002
type: Opaque
Using Secrets
Secrets can be mounted as data volumes or exposed as environment variables to be used by a container in a Pod. Secrets can also be used by other parts of the system, without being directly exposed to the Pod. For example, Secrets 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:
- Create a secret or use an existing one. Multiple Pods can reference the same secret.
- 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. - 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. - Modify your image or command line so that the program looks for files in that directory. Each key in the secret
data
map becomes the filename undermountPath
.
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 .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
You can also control the paths within the volume where Secret keys are projected.
You can 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
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 set the 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 mode for the entire 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: 0400
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.
Note if you kubectl exec
into the Pod, you need to follow the symlink to find
the expected file mode. For example,
Check the secrets file mode on the pod.
kubectl exec mypod -it sh
cd /etc/foo
ls -l
The output is similar to this:
total 0
lrwxrwxrwx 1 root root 15 May 18 00:18 password -> ..data/password
lrwxrwxrwx 1 root root 15 May 18 00:18 username -> ..data/username
Follow the symlink to find the correct file mode.
cd /etc/foo/..data
ls -l
The output is similar to this:
total 8
-r-------- 1 root root 12 May 18 00:18 password
-r-------- 1 root root 5 May 18 00:18 username
You can also use mapping, as in the previous example, and specify different permissions 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: 0777
In this case, the file resulting in /etc/foo/my-group/my-username
will have
permission value of 0777
. If you use JSON, owing to JSON limitations, you
must specify the mode in decimal notation, 511
.
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 base64 decoded and stored inside these files. This is the result of commands executed inside the container from the example above:
ls /etc/foo/
The output is similar to:
username
password
cat /etc/foo/username
The output is similar to:
admin
cat /etc/foo/password
The output is similar to:
1f2d1e2e67df
The program in a container is responsible for reading the secrets from the files.
Mounted Secrets are updated automatically
When a secret currently consumed in a volume is updated, projected keys are eventually updated as well.
The kubelet checks whether the mounted secret is fresh on every periodic sync.
However, the kubelet uses its local cache for getting the current value of the Secret.
The type of the cache is configurable using the ConfigMapAndSecretChangeDetectionStrategy
field in
the KubeletConfiguration struct.
A Secret can be either propagated by watch (default), ttl-based, or by redirecting
all requests directly to the API server.
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 the kubelet sync period + cache
propagation delay, where the cache propagation delay depends on the chosen cache type
(it equals to watch propagation delay, ttl of cache, or zero correspondingly).
Using Secrets as environment variables
To use a secret in an environment variable in a Pod:
- Create a secret or use an existing one. Multiple Pods can reference the same secret.
- 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[].valueFrom.secretKeyRef
. - 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:
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 the environment variables, the secret keys appear as normal environment variables containing the base64 decoded values of the secret data. This is the result of commands executed inside the container from the example above:
echo $SECRET_USERNAME
The output is similar to:
admin
echo $SECRET_PASSWORD
The output is similar to:
1f2d1e2e67df
Environment variables are not updated after a secret update
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.
Immutable Secrets
Kubernetes v1.21 [stable]
The Kubernetes feature Immutable Secrets and ConfigMaps provides an option to set individual Secrets and ConfigMaps as immutable. For clusters that extensively use Secrets (at least tens of thousands of unique Secret to Pod mounts), preventing changes to their data has the following advantages:
- protects you from accidental (or unwanted) updates that could cause applications outages
- improves performance of your cluster by significantly reducing load on kube-apiserver, by closing watches for secrets marked as immutable.
This feature is controlled by the ImmutableEphemeralVolumes
feature gate,
which is enabled by default since v1.19. You can create an immutable
Secret by setting the immutable
field to true
. For example,
apiVersion: v1
kind: Secret
metadata:
...
data:
...
immutable: true
data
field. You can only delete and recreate the Secret.
Existing Pods maintain a mount point to the deleted Secret - it is recommended to recreate
these pods.
Using imagePullSecrets
The imagePullSecrets
field is a list of references to secrets in the same namespace.
You can use an imagePullSecrets
to pass a secret that contains a Docker (or other) image registry
password to the kubelet. The kubelet uses this information to pull a private image on behalf of your Pod.
See the PodSpec API for more information about the imagePullSecrets
field.
Manually specifying an imagePullSecret
You can learn how to specify ImagePullSecrets
from the container images documentation.
Arranging for imagePullSecrets to be automatically attached
You can manually create imagePullSecrets
, and reference it from
a ServiceAccount. Any Pods created with that ServiceAccount
or created with that ServiceAccount by default, will get their imagePullSecrets
field set to that of the service account.
See Add ImagePullSecrets to a service account
for a detailed explanation of that process.
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 resources reside in a namespace. Secrets can only be referenced by Pods in that same namespace.
Individual secrets are limited to 1MiB in size. This is to discourage creation of very large secrets which would exhaust the API server 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.
The kubelet only supports the use of secrets for Pods where the secrets
are obtained from the API server.
This includes any Pods created using kubectl
, or indirectly via a replication
controller. It does not include Pods created as a result of the kubelet
--manifest-url
flag, its --config
flag, or its REST API (these are
not common ways to create Pods).
The spec
of a static Pod cannot refer to a Secret
or any other API objects.
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 (secretKeyRef
field) to keys that do not exist in a named Secret
will prevent the Pod from starting.
Secrets used to populate environment variables by the envFrom
field 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 that contains 2 invalid keys: 1badkey
and 2alsobad
.
kubectl get events
The output is similar to:
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.
Secret and Pod lifetime interaction
When a Pod is created by calling the Kubernetes API, there is no check if 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, the 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.
Use cases
Use-Case: As container environment variables
Create a secret
apiVersion: v1
kind: Secret
metadata:
name: mysecret
type: Opaque
data:
USER_NAME: YWRtaW4=
PASSWORD: MWYyZDFlMmU2N2Rm
Create the Secret:
kubectl apply -f mysecret.yaml
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.
apiVersion: v1
kind: Pod
metadata:
name: secret-test-pod
spec:
containers:
- name: test-container
image: k8s.gcr.io/busybox
command: [ "/bin/sh", "-c", "env" ]
envFrom:
- secretRef:
name: mysecret
restartPolicy: Never
Use-Case: Pod with ssh keys
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
The output is similar to:
secret "ssh-key-secret" created
You can also create a kustomization.yaml
with a secretGenerator
field containing ssh keys.
Now you can create a Pod which references the secret with the ssh key and consumes it in a volume:
apiVersion: v1
kind: Pod
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:
/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 production credentials and another Pod which consumes a secret with test environment credentials.
You can create a kustomization.yaml
with a secretGenerator
field or run
kubectl create secret
.
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
You can also 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
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$zDsb=
, you should execute the command this way:
kubectl create secret generic dev-db-secret --from-literal=username=devuser --from-literal=password='S!B\*d$zDsb='
You do not need to escape special characters in passwords from files (--from-file
).
Now make the Pods:
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
Add the pods to the same kustomization.yaml:
cat <<EOF >> kustomization.yaml
resources:
- pod.yaml
EOF
Apply all those objects on the API server by running:
kubectl apply -k .
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
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.
You could further simplify the base Pod specification by using two service accounts:
prod-user
with theprod-db-secret
test-user
with thetest-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
Use-case: dotfiles in a secret volume
You can make your data "hidden" by defining a key that begins with a dot.
This key represents a dotfile or "hidden" file. For example, when the following secret
is mounted into a volume, secret-volume
:
apiVersion: v1
kind: Secret
metadata:
name: dotfile-secret
data:
.secret-file: dmFsdWUtMg0KDQo=
---
apiVersion: v1
kind: Pod
metadata:
name: secret-dotfiles-pod
spec:
volumes:
- name: secret-volume
secret:
secretName: dotfile-secret
containers:
- name: dotfile-test-container
image: k8s.gcr.io/busybox
command:
- ls
- "-l"
- "/etc/secret-volume"
volumeMounts:
- name: secret-volume
readOnly: true
mountPath: "/etc/secret-volume"
The volume will contain a single file, called .secret-file
, and
the dotfile-test-container
will have this file present at the path
/etc/secret-volume/.secret-file
.
ls -l
;
you must use ls -la
to see them when listing directory contents.
Use-case: Secret visible to one container in a Pod
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 (for example, 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.
Best practices
Clients that use the Secret API
When deploying applications that interact with the Secret API, you should limit access using authorization policies such as RBAC.
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 watch
and 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 of all secrets that are in that namespace. The ability to
watch
and list
all secrets in a cluster should be reserved for only the most
privileged, system-level components.
Applications that need to access the Secret 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.
Security properties
Protections
Because secrets 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 precautions with Secrets, such as avoiding writing them to disk where possible.
A secret is only sent to a node if a Pod on that node requires it.
The kubelet stores the secret into a tmpfs
so that the secret is not written
to disk storage. Once the Pod that depends on the secret is deleted, the kubelet
will delete its local copy of the secret data as well.
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
Pod level.
On most Kubernetes distributions, communication between users and the API server, and from the API server to the kubelets, is protected by SSL/TLS. Secrets are protected when transmitted over these channels.
Kubernetes v1.13 [beta]
You can enable encryption at rest for secret data, so that the secrets are not stored in the clear into etcd.
Risks
- In the API server, secret data is stored in etcd;
therefore:
- Administrators should enable encryption at rest for cluster data (requires v1.13 or later).
- Administrators should limit access to etcd to admin users.
- Administrators may want to wipe/shred disks used by etcd when no longer in use.
- If running etcd in a cluster, administrators should make sure to use SSL/TLS for etcd peer-to-peer communication.
- If you configure the secret through a manifest (JSON or YAML) file which has the secret data encoded as base64, sharing this file or checking it in to a source repository means the secret is compromised. Base64 encoding is not an encryption method and is considered the same as plain text.
- Applications still need to protect the value of secret after reading it from the volume, such as not accidentally logging it or transmitting it to an untrusted party.
- A user who can create a Pod that uses a secret can also see the value of that secret. Even if the API server policy does not allow that user to read the Secret, the user could run a Pod which exposes the secret.
What's next
- Learn how to manage Secret using
kubectl
- Learn how to manage Secret using config file
- Learn how to manage Secret using kustomize
- Read the API reference for
Secret