Secrets
Kubernetes Secrets let you store and manage sensitive information, such as passwords, OAuth tokens, and ssh keys. Storing confidential information in a Secret is safer and more flexible than putting it verbatim in a PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. definition or in a container imageStored instance of a container that holds a set of software needed to run an application. . See Secrets design document for more information.
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. 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 volumeA directory containing data, accessible to the containers in a pod. mounted on one or more of its containers.
- By the 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 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 API server, this is the recommended workflow.
See the ServiceAccount documentation for more information on how service accounts work.
Creating your own Secrets
Creating a Secret Using kubectl
Secrets can contain user credentials required by Pods to access a database.
For example, a database connection string
consists of a username and password. You can store the username in a file ./username.txt
and the password in a file ./password.txt
on your local machine.
# Create files needed for the rest of the example.
echo -n 'admin' > ./username.txt
echo -n '1f2d1e2e67df' > ./password.txt
The kubectl create secret
command packages these files into a Secret and creates
the object on the API server.
The name of a Secret object must be a valid
DNS subdomain name.
kubectl create secret generic db-user-pass --from-file=./username.txt --from-file=./password.txt
The output is similar to:
secret "db-user-pass" 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 isS!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
).
You can check that the secret was created:
kubectl get secrets
The output is similar to:
NAME TYPE DATA AGE
db-user-pass Opaque 2 51s
You can view a description of the secret:
kubectl describe secrets/db-user-pass
The output is similar to:
Name: db-user-pass
Namespace: default
Labels: <none>
Annotations: <none>
Type: Opaque
Data
====
password.txt: 12 bytes
username.txt: 5 bytes
Note: The commandskubectl get
andkubectl describe
avoid showing the contents of a secret by default. This is to protect the secret from being exposed accidentally to an onlooker, or from being stored in a terminal log.
See decoding a secret to learn how to view the contents of a secret.
Creating a Secret manually
You can also create a Secret in a file first, in JSON or YAML format,
and then create that object.
The name of a Secret object must be a valid
DNS subdomain name.
The Secret
contains two maps:
data
and stringData
. The data
field is used to store arbitrary data, encoded using
base64. The stringData
field is provided for convenience, and allows you to provide
secret data as unencoded strings.
For example, to store two strings in a Secret using the data
field, convert
the strings to base64 as follows:
echo -n 'admin' | base64
The output is similar to:
YWRtaW4=
echo -n '1f2d1e2e67df' | base64
The output is similar to:
MWYyZDFlMmU2N2Rm
Write a Secret that looks like this:
apiVersion: v1
kind: Secret
metadata:
name: mysecret
type: Opaque
data:
username: YWRtaW4=
password: MWYyZDFlMmU2N2Rm
Now create the Secret using kubectl apply
:
kubectl apply -f ./secret.yaml
The output is similar to:
secret "mysecret" created
For certain scenarios, you may wish to use the stringData
field instead. This
field allows you to put a non-base64 encoded string directly into the Secret,
and the string will be encoded for you when the Secret is created or updated.
A practical example of this might be where you are deploying an application that uses a Secret to store a configuration file, and you want to populate parts of that configuration file during your deployment process.
For example, if your application uses the following configuration file:
apiUrl: "https://my.api.com/api/v1"
username: "user"
password: "password"
You could store this in a Secret using the following definition:
apiVersion: v1
kind: Secret
metadata:
name: mysecret
type: Opaque
stringData:
config.yaml: |-
apiUrl: "https://my.api.com/api/v1"
username: {{username}}
password: {{password}}
Your deployment tool could then replace the {{username}}
and {{password}}
template variables before running kubectl apply
.
The stringData
field is a write-only convenience field. It is never output when
retrieving Secrets. For example, if you run the following command:
kubectl get secret mysecret -o yaml
The output is similar to:
apiVersion: v1
kind: Secret
metadata:
creationTimestamp: 2018-11-15T20:40:59Z
name: mysecret
namespace: default
resourceVersion: "7225"
uid: c280ad2e-e916-11e8-98f2-025000000001
type: Opaque
data:
config.yaml: YXBpVXJsOiAiaHR0cHM6Ly9teS5hcGkuY29tL2FwaS92MSIKdXNlcm5hbWU6IHt7dXNlcm5hbWV9fQpwYXNzd29yZDoge3twYXNzd29yZH19
If a field, such as username
, is specified in both data
and stringData
,
the value from stringData
is used. For example, the following Secret definition:
apiVersion: v1
kind: Secret
metadata:
name: mysecret
type: Opaque
data:
username: YWRtaW4=
stringData:
username: administrator
Results in the following Secret:
apiVersion: v1
kind: Secret
metadata:
creationTimestamp: 2018-11-15T20:46:46Z
name: mysecret
namespace: default
resourceVersion: "7579"
uid: 91460ecb-e917-11e8-98f2-025000000001
type: Opaque
data:
username: YWRtaW5pc3RyYXRvcg==
Where YWRtaW5pc3RyYXRvcg==
decodes to administrator
.
The keys of data
and stringData
must consist of alphanumeric characters,
‘-’, ‘_’ or ‘.’.
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 thebase64
utility on Darwin/macOS, users should avoid using the-b
option to split long lines. Conversely, Linux users should add the option-w 0
tobase64
commands or the pipelinebase64 | tr -d '\n'
if the-w
option is not available.
Creating a Secret from a generator
Since Kubernetes v1.14, kubectl
supports managing objects using Kustomize. Kustomize provides resource Generators to
create Secrets and ConfigMaps. The Kustomize generators should be specified in a
kustomization.yaml
file inside a directory. After generating the Secret,
you can create the Secret on the API server with kubectl apply
.
Generating a Secret from files
You can generate a Secret by defining a secretGenerator
from the
files ./username.txt and ./password.txt:
cat <<EOF >./kustomization.yaml
secretGenerator:
- name: db-user-pass
files:
- username.txt
- password.txt
EOF
Apply the directory, containing the kustomization.yaml
, to create the Secret.
kubectl apply -k .
The output is similar to:
secret/db-user-pass-96mffmfh4k created
You can check that the secret was created:
kubectl get secrets
The output is similar to:
NAME TYPE DATA AGE
db-user-pass-96mffmfh4k Opaque 2 51s
kubectl describe secrets/db-user-pass-96mffmfh4k
The output is similar to:
Name: db-user-pass
Namespace: default
Labels: <none>
Annotations: <none>
Type: Opaque
Data
====
password.txt: 12 bytes
username.txt: 5 bytes
Generating a Secret from string literals
You can create a Secret by defining a secretGenerator
from literals username=admin
and password=secret
:
cat <<EOF >./kustomization.yaml
secretGenerator:
- name: db-user-pass
literals:
- username=admin
- password=secret
EOF
Apply the directory, containing the kustomization.yaml
, to create the Secret.
kubectl apply -k .
The output is similar to:
secret/db-user-pass-dddghtt9b5 created
Note: When a Secret is generated, the Secret name is created by hashing the Secret data and appending this value to the name. This ensures that a new Secret is generated each time the data is modified.
Decoding a Secret
Secrets can be retrieved by running kubectl get secret
.
For example, you can view the Secret created in the previous section by
running the following command:
kubectl get secret mysecret -o yaml
The output is similar to:
apiVersion: v1
kind: Secret
metadata:
creationTimestamp: 2016-01-22T18:41:56Z
name: mysecret
namespace: default
resourceVersion: "164619"
uid: cfee02d6-c137-11e5-8d73-42010af00002
type: Opaque
data:
username: YWRtaW4=
password: MWYyZDFlMmU2N2Rm
Decode the password
field:
echo 'MWYyZDFlMmU2N2Rm' | base64 --decode
The output is similar to:
1f2d1e2e67df
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 variablesContainer environment variables are name=value pairs that provide useful information into containers running in a Pod. 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: 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 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: 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 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 simply 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).
Note: A container using a Secret as a subPath volume mount will not receive Secret updates.
Kubernetes v1.18
alpha
- The version names contain alpha (e.g. v1alpha1).
- Might be buggy. Enabling the feature may expose bugs. Disabled by default.
- Support for feature may be dropped at any time without notice.
- The API may change in incompatible ways in a later software release without notice.
- Recommended for use only in short-lived testing clusters, due to increased risk of bugs and lack of long-term support.
The Kubernetes alpha 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.
To use this feature, enable the ImmutableEmphemeralVolumes
feature gate and set
your Secret or ConfigMap immutable
field to true
. For example:
apiVersion: v1
kind: Secret
metadata:
...
data:
...
immutable: true
Note: Once a Secret or ConfigMap is marked as immutable, it is not possible to revert this change nor to mutate the contents of thedata
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 Secrets as environment variables
To use a secret in an environment variableContainer environment variables are name=value pairs that provide useful information into containers running in a Pod. 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 an 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
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.
Automatic mounting of manually created Secrets
Manually created secrets (for example, 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.
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 namespaceAn abstraction used by Kubernetes to support multiple virtual clusters on the same physical cluster. . 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.)
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: 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.
Caution: 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 this account if the users are compromised.
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
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 isS!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
.
Note: Files beginning with dot characters are hidden from the output ofls -l
; you must usels -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
- The version names contain beta (e.g. v2beta3).
- Code is well tested. Enabling the feature is considered safe. Enabled by default.
- Support for the overall feature will not be dropped, though details may change.
- The schema and/or semantics of objects may change in incompatible ways in a subsequent beta or stable release. When this happens, we will provide instructions for migrating to the next version. This may require deleting, editing, and re-creating API objects. The editing process may require some thought. This may require downtime for applications that rely on the feature.
- Recommended for only non-business-critical uses because of potential for incompatible changes in subsequent releases. If you have multiple clusters that can be upgraded independently, you may be able to relax this restriction.
- Please do try our beta features and give feedback on them! After they exit beta, it may not be practical for us to make more changes.
You can enable encryption at rest for secret data, so that the secrets are not stored in the clear into etcdConsistent and highly-available key value store used as Kubernetes’ backing store for all cluster data. .
Risks
- In the API server, secret data is stored in etcdConsistent and highly-available key value store used as Kubernetes’ backing store for all cluster data.
;
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.
- Currently, anyone with root permission on any node can read any secret from the API server, by impersonating the kubelet. It is a planned feature to only send secrets to nodes that actually require them, to restrict the impact of a root exploit on a single node.
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