Kubernetes External Secrets

Kubernetes External Secrets allows you to use external secret management systems, like AWS Secrets Manager or HashiCorp Vault, to securely add secrets in Kubernetes. Read more about the design and motivation for Kubernetes External Secrets on the GoDaddy Engineering Blog.

How it works

The project extends the Kubernetes API by adding a ExternalSecrets object using Custom Resource Definition and a controller to implement the behavior of the object itself.

An ExternalSecret declares how to fetch the secret data, while the controller converts all ExternalSecrets to Secrets. The conversion is completely transparent to Pods that can access Secrets normally.

System architecture

1. ExternalSecrets are added in the cluster (e.g., kubectl apply -f external-secret-example.yml)
2. Controller fetches ExternalSecrets using the Kubernetes API
3. Controller uses ExternalSecrets to fetch secret data from external providers (e.g, AWS Secrets Manager)
4. Controller upsert Secrets
5. Pods can access Secrets normally

How to use it

Install with Helm

The official helm chart can be used to create the kubernetes-external-secrets resources and Deployment on a Kubernetes cluster using the Helm package manager.

$ helm repo add external-secrets https://godaddy.github.io/kubernetes-external-secrets/
$ helm install external-secrets/kubernetes-external-secrets

For more details about configuration see the helm chart docs

Install with kubectl

If you don't want to install helm on your cluster and just want to use kubectl to install kubernetes-external-secrets, you could get the helm client cli first and then use the following sample command to generate kubernetes manifests:

$ helm template -f charts/kubernetes-external-secrets/values.yaml --output-dir ./output_dir ./charts/kubernetes-external-secrets/

The generated kubernetes manifests will be in ./output_dir and can be applied to deploy kubernetes-external-secrets to the cluster.

Use IAM credentials for Secrets Manager access

If not running on EKS you will have to use an IAM user (in lieu of a role). Set AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY env vars in the session/pod. You can use envVarsFromSecret in the helm chart to create these env vars from existing k8s secrets

Additionally, you can specify a roleArn which will be assumed before retrieving the secret. You can limit the range of roles which can be assumed by this particular namespace by using annotations on the namespace resource. The annotation key is configurable (see above). The annotation value is evaluated as a regular expression and tries to match the roleArn.

kind: Namespace
metadata:
  name: iam-example
  annotations:
    # annotation key is configurable
    iam.amazonaws.com/permitted: "arn:aws:iam::123456789012:role/.*"

Add a secret

Add your secret data to your backend. For example, AWS Secrets Manager:

aws secretsmanager create-secret --name hello-service/password --secret-string "1234"

AWS Parameter Store:

aws ssm put-parameter --name "/hello-service/password" --type "String" --value "1234"

and then create a hello-service-external-secret.yml file:

apiVersion: 'kubernetes-client.io/v1'
kind: ExternalSecret
metadata:
  name: hello-service
spec:
  backendType: secretsManager
  # optional: specify role to assume when retrieving the data
  roleArn: arn:aws:iam::123456789012:role/test-role
  data:
    - key: hello-service/password
      name: password
  # optional: specify a template with any additional markup you would like added to the downstream Secret resource.
  # This template will be deep merged without mutating any existing fields. For example: you cannot override metadata.name.
  template:
    metadata:
      annotations:
        cat: cheese
      labels:
        dog: farfel

or

apiVersion: 'kubernetes-client.io/v1'
kind: ExternalSecret
metadata:
  name: hello-service
spec:
  backendType: systemManager
  data:
    - key: /hello-service/password
      name: password

The following IAM policy allows a user or role to access parameters matching prod-*.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "ssm:GetParameter",
      "Resource": "arn:aws:ssm:us-west-2:123456789012:parameter/prod-*"
    }
  ]
}

The IAM policy for Secrets Manager is similar (see docs):

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "secretsmanager:GetResourcePolicy",
        "secretsmanager:GetSecretValue",
        "secretsmanager:DescribeSecret",
        "secretsmanager:ListSecretVersionIds"
      ],
      "Resource": [
        "arn:aws:secretsmanager:us-west-2:111122223333:secret:aes128-1a2b3c",
        "arn:aws:secretsmanager:us-west-2:111122223333:secret:aes192-4D5e6F",
        "arn:aws:secretsmanager:us-west-2:111122223333:secret:aes256-7g8H9i"
      ]
    }
  ]
}

Save the file and run:

kubectl apply -f hello-service-external-secret.yml

Wait a few minutes and verify that the associated Secret has been created:

kubectl get secret hello-service -o=yaml

The Secret created by the controller should look like:

apiVersion: v1
kind: Secret
metadata:
  name: hello-service
  annotations:
    cat: cheese
  labels:
    dog: farfel
type: Opaque
data:
  password: MTIzNA==

Deprecations

A few properties has changed name overtime, we still maintain backwards compatbility with these but they will eventually be removed, and they are not validated using the CRD validation.

Old	New
secretDescriptor	spec
spec.type	spec.template.type
spec.properties	spec.data
backendType: secretManager	backendType: secretsManager

Backends

kubernetes-external-secrets supports AWS Secrets Manager, AWS System Manager, and Hashicorp Vault.

AWS Secrets Manager

kubernetes-external-secrets supports both JSON objects ("Secret key/value" in the AWS console) or strings ("Plaintext" in the AWS console). Using JSON objects is useful when you need to atomically update multiple values. For example, when rotating a client certificate and private key.

When writing an ExternalSecret for a JSON object you must specify the properties to use. For example, if we add our hello-service credentials as a single JSON object:

aws secretsmanager create-secret --region us-west-2 --name hello-service/credentials --secret-string '{"username":"admin","password":"1234"}'

We can declare which properties we want from hello-service/credentials:

apiVersion: kubernetes-client.io/v1
kind: ExternalSecret
metadata:
  name: hello-service
spec:
  backendType: secretsManager
  # optional: specify role to assume when retrieving the data
  roleArn: arn:aws:iam::123456789012:role/test-role
  data:
    - key: hello-service/credentials
      name: password
      property: password
    - key: hello-service/credentials
      name: username
      property: username
    - key: hello-service/credentials
      name: password
      # Version Stage in Secrets Manager
      versionStage: AWSPREVIOUS
      property: password_previous

alternatively you can use dataFrom and get all the values from hello-service/credentials:

apiVersion: kubernetes-client.io/v1
kind: ExternalSecret
metadata:
  name: hello-service
spec:
  backendType: secretsManager
  # optional: specify role to assume when retrieving the data
  roleArn: arn:aws:iam::123456789012:role/test-role
  dataFrom:
    - hello-service/credentials

data and dataFrom can of course be combined, any naming conflicts will use the last defined, with data overriding dataFrom

apiVersion: kubernetes-client.io/v1
kind: ExternalSecret
metadata:
  name: hello-service
spec:
  backendType: secretsManager
  # optional: specify role to assume when retrieving the data
  roleArn: arn:aws:iam::123456789012:role/test-role
  dataFrom:
    - hello-service/credentials
  data:
    - key: hello-service/migration-credentials
      name: password
      property: password

Hashicorp Vault

kubernetes-external-secrets supports fetching secrets from Hashicorp Vault, using the Kubernetes authentication method.

You will need to set the VAULT_ADDR environment variables so that kubernetes-external-secrets knows which endpoint to connect to, then create ExternalSecret definitions as follows:

apiVersion: 'kubernetes-client.io/v1'
kind: ExternalSecret
metadata:
  name: hello-vault-service
spec:
  backendType: vault
  # Your authentication mount point, e.g. "kubernetes"
  vaultMountPoint: my-kubernetes-vault-mount-point
  # The vault role that will be used to fetch the secrets
  # This role will need to be bound to kubernetes-external-secret's ServiceAccount; see Vault's documentation:
  # https://www.vaultproject.io/docs/auth/kubernetes.html
  vaultRole: my-vault-role
  data:
  - name: password
    # The full path of the secret to read, as in `vault read secret/data/hello-service/credentials`
    key: secret/data/hello-service/credentials
    property: password
  # Vault values are matched individually. If you have several keys in your Vault secret, you will need to add them all separately
  - name: api-key
    key: secret/data/hello-service/credentials
    property: api-key

Metrics

kubernetes-external-secrets exposes the following metrics over a prometheus endpoint:

Metric	Description	Example
sync_calls	This metric counts the number of sync calls by backend, secret name and status	sync_calls{name="foo",namespace="example",backend="foo",status="success"} 1

Development

Minikube is a tool that makes it easy to run a Kubernetes cluster locally.

Start minikube and the daemon. This creates the CustomerResourceDefinition, and starts to process ExternalSecrets:

minikube start

npm run nodemon

Development with localstack

Localstack mocks AWS services locally so you can test without connecting to AWS.

Run localstack in a seperate terminal window

npm run localstack

Start minikube as above

minikube start

Run the daemon with localstack

npm run local

Add secrets using the AWS cli (example)

AWS_ACCESS_KEY_ID=foobar AWS_SECRET_ACCESS_KEY=foobar aws --region=us-west-2 --endpoint-url=http://localhost:4584 secretsmanager create-secret --name hello-service/password --secret-string "1234"