"Sealed Secrets" for Kubernetes

Problem: "I can manage all my K8s config in git, except Secrets."

Solution: Encrypt your Secret into a SealedSecret, which is safe to store - even to a public repository. The SealedSecret can be decrypted only by the controller running in the target cluster and nobody else (not even the original author) is able to obtain the original Secret from the SealedSecret.

Installation

See https://github.com/bitnami-labs/sealed-secrets/releases for the latest release.

See additional TPR->CRD migration section below if updating an existing Sealed Secrets installation from Kubernetes <= 1.7

$ release=$(curl --silent "https://api.github.com/repos/bitnami-labs/sealed-secrets/releases/latest" | sed -n 's/.*"tag_name": *"\([^"]*\)".*/\1/p')

# Install client-side tool into /usr/local/bin/
$ GOOS=$(go env GOOS)
$ GOARCH=$(go env GOARCH)
$ wget https://github.com/bitnami-labs/sealed-secrets/releases/download/$release/kubeseal-$GOOS-$GOARCH
$ sudo install -m 755 kubeseal-$GOOS-$GOARCH /usr/local/bin/kubeseal

# Install SealedSecret TPR (for k8s < 1.7)
$ kubectl create -f https://github.com/bitnami-labs/sealed-secrets/releases/download/$release/sealedsecret-tpr.yaml

# Install SealedSecret CRD (for k8s >= 1.7)
$ kubectl create -f https://github.com/bitnami-labs/sealed-secrets/releases/download/$release/sealedsecret-crd.yaml

# Install server-side controller into kube-system namespace (by default)
$ kubectl create -f https://github.com/bitnami-labs/sealed-secrets/releases/download/$release/controller.yaml

After the SealedSecret resource is created with either sealedsecret-tpr.yaml or sealedsecret-crd.yaml (depending on Kubernetes version), controller.yaml will install the controller into kube-system namespace, create a service account and necessary RBAC roles.

After a few moments, the controller will start, generate a key pair, and be ready for operation. If it does not, check the controller logs.

The key certificate (public key portion) is used for sealing secrets, and needs to be available wherever kubeseal is going to be used. The certificate is not secret information, although you need to ensure you are using the correct file.

kubeseal will fetch the certificate from the controller at runtime (requires secure access to the Kubernetes API server), which is convenient for interactive use. The recommended automation workflow is to store the certificate to local disk with kubeseal --fetch-cert >mycert.pem, and use it offline with kubeseal --cert mycert.pem. The certificate is also printed to the controller log on startup.

Installation from source

If you just want the latest client tool, it can be installed into $GOPATH/bin with:

% go get github.com/bitnami-labs/sealed-secrets/cmd/kubeseal

For a more complete development environment, clone the repository and use the Makefile:

% git clone https://github.com/bitnami-labs/sealed-secrets.git
% cd sealed-secrets

# Build client-side tool and controller binaries
% make

Migration from SealedSecret TPR to CRD (ie: K8s <1.7 to >1.7)

Kubernetes migrated the way custom resources are declared from TPR (ThirdPartyResource) to CRD (CustomResourceDefinition). The migration has a number of steps, but is easy, and preserves existing SealedSecrets.

• The controller is temporarily disabled during the migration, so changes to SealedSecrets will not propagate to Secrets until the controller is restored.
• Existing (decrypted) Secrets remain available throughout.
• This only affects the way the custom resource is defined, and API clients are able to interact with both versions of SealedSecrets without requiring changes.

The following is an adaption of the generic migration doc for Sealed Secrets. See the generic documentation for more information on the process.

1. Be running k8s 1.7.x. Kubernetes 1.7.x is the only Kubernetes release that simultaneously supports both TPRs and CRDs.

2. Install the CRD definition.

   $ release=$(curl --silent "https://api.github.com/repos/bitnami-labs/sealed-secrets/releases/latest" | sed -n 's/.*"tag_name": *"\([^"]*\)".*/\1/p')
   $ kubectl create -f https://github.com/bitnami-labs/sealed-secrets/releases/download/$release/sealedsecret-crd.yaml
   

   Wait until the CRD Established condition becomes True.

   $ kubectl get crd sealedsecrets.bitnami.com -o 'jsonpath={.status.conditions[?(@.type=="Established")].status}'
   

   At this point the TPR is still authoritative. NB: The CRD name is sealedsecrets.bitnami.com, whereas the TPR name is sealed-secret.bitnami.com.

3. Stop controller. For maximum safety, also pause any other processes you have that might modify SealedSecrets during the following steps.

   $ kubectl scale --replicas=0 -n kube-system deployment/sealed-secrets-controller
   

4. Back up existing SealedSecrets data and TPR definition, just in case.

   $ kubectl get sealedsecrets --all-namespaces -o yaml > sealedsecrets.yaml
   $ kubectl get thirdpartyresource sealed-secret.bitnami.com -o yaml --export > tpr.yaml
   

5. Delete TPR definition.

   $ kubectl delete thirdpartyresource sealed-secret.bitnami.com
   

   NB: The CRD name is sealedsecrets.bitnami.com, whereas the TPR name is sealed-secret.bitnami.com.

   This will trigger the Kubernetes TPR controller to migrate existing SealedSecrets to the CRD.

6. Once the migration completes, the resources will be available via the CRD.

   $ kubectl get sealedsecrets --all-namespaces -o yaml
   

   If the copy fails for some reason and needs to be reverted, the TPR definition can be restored with:

   $ kubectl create -f tpr.yaml
   

7. Restore controller, and any other paused processes.

   $ kubectl scale --replicas=1 -n kube-system deployment/sealed-secrets-controller
   

Usage

# Create a json/yaml-encoded Secret somehow:
# (note use of `--dry-run` - this is just a local file!)
$ kubectl create secret generic mysecret --dry-run --from-literal=foo=bar -o json >mysecret.json

# This is the important bit:
$ kubeseal <mysecret.json >mysealedsecret.json

# mysealedsecret.json is safe to upload to github, post to twitter,
# etc.  Eventually:
$ kubectl create -f mysealedsecret.json

# Profit!
$ kubectl get secret mysecret

Note the SealedSecret and Secret must have the same namespace and name. This is a feature to prevent other users on the same cluster from re-using your sealed secrets. kubeseal reads the namespace from the input secret, accepts an explicit --namespace arg, and uses the kubectl default namespace (in that order). Any labels, annotations, etc on the original Secret are preserved, but not automatically reflected in the SealedSecret.

By design, this scheme does not authenticate the user. In other words, anyone can create a SealedSecret containing any Secret they like (provided the namespace/name matches). It is up to your existing config management workflow, cluster RBAC rules, etc to ensure that only the intended SealedSecret is uploaded to the cluster. The only change from existing Kubernetes is that the contents of the Secret are now hidden while outside the cluster.

Details

This controller adds a new SealedSecret custom resource. The interesting part of a SealedSecret is a base64-encoded asymmetrically encrypted Secret.

The controller looks for a cluster-wide private/public key pair on startup, and generates a new 4096 bit (by default) RSA key pair if not found. The key is persisted in a regular Secret in the same namespace as the controller. The public key portion of this (in the form of a self-signed certificate) should be made publicly available to anyone wanting to use SealedSecrets with this cluster. The certificate is printed to the controller log at startup, and available via an HTTP GET to /v1/cert.pem on the controller.

During encryption, each value in the original Secret is symmetrically encrypted using AES-GCM (AES-256) with a randomly-generated single-use 32 byte session key. The session key is then asymmetrically encrypted with the controller's public key using RSA-OAEP (using SHA256), and the original Secret's namespace/name as the OAEP input parameter (aka label). The final output is: 2 byte encrypted session key length || encrypted session key || encrypted Secret.

Note that during decryption by the controller, the SealedSecret's namespace/name is used as the OAEP input parameter, ensuring that the SealedSecret and Secret are tied to the same namespace and name.

The generated Secret is marked as "owned" by the SealedSecret and will be garbage collected if the SealedSecret is deleted.

FAQ

• Will you still be able to decrypt if you no longer have access to your cluster?

No, the private key is only stored in the Secret managed by the controller (unless you have some other backup of your k8s objects). There are no backdoors - without that private key, then you can't decrypt the SealedSecrets. If you can't get to the Secret with the encryption key, and you also can't get to the decrypted versions of your Secrets live in the cluster, then you will need to regenerate new passwords for everything, seal them again with a new sealing key, etc.

• How can I do a backup of my SealedSecrets?

If you do want to make a backup of the encryption private key, it's easy to do from an account with suitable access and:

kubectl get secret -n kube-system sealed-secrets-key -o yaml >master.key

NOTE: This is the controller's public + private key and should be kept omg-safe!

To restore from a backup after some disaster, just put that secret back before starting the controller - or if the controller was already started, replace the newly-created secret and restart the controller:

kubectl replace secret -n kube-system sealed-secrets-key master.key kubectl delete pod -n kube-system -l name=sealed-secrets-controller

• What flags are available for kubeseal?

You can check the flags available using kubeseal --help.