Manage Kubernetes secrets with SOPS

In order to store secrets safely in a public or private Git repository, you can use SOPS CLI to encrypt Kubernetes secrets with OpenPGP, AWS KMS, GCP KMS and Azure Key Vault.

Prerequisites

To follow this guide you’ll need a Kubernetes cluster with the GitOps toolkit controllers installed on it. Please see the get started guide or the installation guide.

Install gnupg and SOPS:

brew install gnupg sops

Generate a GPG key

Generate a GPG/OpenPGP key with no passphrase (%no-protection):

export KEY_NAME="cluster0.yourdomain.com"
export KEY_COMMENT="flux secrets"

gpg --batch --full-generate-key <<EOF
%no-protection
Key-Type: 1
Key-Length: 4096
Subkey-Type: 1
Subkey-Length: 4096
Expire-Date: 0
Name-Comment: ${KEY_COMMENT}
Name-Real: ${KEY_NAME}
EOF

The above configuration creates an rsa4096 key that does not expire. For a full list of options to consider for your environment, see Unattended GPG key generation.

Retrieve the GPG key fingerprint (second row of the sec column):

gpg --list-secret-keys "${KEY_NAME}"

sec   rsa4096 2020-09-06 [SC]
      1F3D1CED2F865F5E59CA564553241F147E7C5FA4

Store the key fingerprint as an environment variable:

export KEY_FP=1F3D1CED2F865F5E59CA564553241F147E7C5FA4

Export the public and private keypair from your local GPG keyring and create a Kubernetes secret named sops-gpg in the flux-system namespace:

gpg --export-secret-keys --armor "${KEY_FP}" |
kubectl create secret generic sops-gpg \
--namespace=flux-system \
--from-file=sops.asc=/dev/stdin

It’s a good idea to back up this secret-key/K8s-Secret with a password manager or offline storage. Also consider deleting the secret decryption key from your machine:

gpg --delete-secret-keys "${KEY_FP}"

Configure in-cluster secrets decryption

Register the Git repository on your cluster:

flux create source git my-secrets \
--url=https://github.com/my-org/my-secrets \
--branch=main

Create a kustomization for reconciling the secrets on the cluster:

flux create kustomization my-secrets \
--source=my-secrets \
--path=./clusters/cluster0 \
--prune=true \
--interval=10m \
--decryption-provider=sops \
--decryption-secret=sops-gpg

Note that the sops-gpg can contain more than one key, SOPS will try to decrypt the secrets by iterating over all the private keys until it finds one that works.

Optional: Export the public key into the Git directory

Commit the public key to the repository so that team members who clone the repo can encrypt new files:

gpg --export --armor "${KEY_FP}" > ./clusters/cluster0/.sops.pub.asc

Check the file contents to ensure it’s the public key before adding it to the repo and committing.

git add ./clusters/cluster0/.sops.pub.asc
git commit -am 'Share GPG public key for secrets generation'

Team members can then import this key when they pull the Git repository:

gpg --import ./clusters/cluster0/.sops.pub.asc

Configure the Git directory for encryption

Write a SOPS config file to the specific cluster or namespace directory used to store encrypted objects with this particular GPG key’s fingerprint.

cat <<EOF > ./clusters/cluster0/.sops.yaml
creation_rules:
  - path_regex: .*.yaml
    encrypted_regex: ^(data|stringData)$
    pgp: ${KEY_FP}
EOF

This config applies recursively to all sub-directories. Multiple directories can use separate SOPS configs. Contributors using the sops CLI to create and encrypt files won’t have to worry about specifying the proper key for the target cluster or namespace.

encrypted_regex helps encrypt the data and stringData fields for Secrets. You may wish to add other fields if you are encrypting other types of Objects.

Encrypting secrets using OpenPGP

Generate a Kubernetes secret manifest with kubectl:

kubectl -n default create secret generic basic-auth \
--from-literal=user=admin \
--from-literal=password=change-me \
--dry-run=client \
-o yaml > basic-auth.yaml

Encrypt the secret with SOPS using your GPG key:

sops --encrypt --in-place basic-auth.yaml

You can now commit the encrypted secret to your Git repository.

Encrypting secrets using age

age is a simple, modern alternative to OpenPGP. It’s recommended to use age over OpenPGP, if possible.

Encrypting with age follows the same workflow than PGP.

Generate an age key with age using age-keygen:

$ age-keygen -o age.agekey
Public key: age1helqcqsh9464r8chnwc2fzj8uv7vr5ntnsft0tn45v2xtz0hpfwq98cmsg

Create a secret with the age private key, the key name must end with .agekey to be detected as an age key:

cat age.agekey |
kubectl create secret generic sops-age \
--namespace=flux-system \
--from-file=age.agekey=/dev/stdin

Use sops and the age public key to encrypt a Kubernetes secret:

sops --age=age1helqcqsh9464r8chnwc2fzj8uv7vr5ntnsft0tn45v2xtz0hpfwq98cmsg \
--encrypt --encrypted-regex '^(data|stringData)$' --in-place basic-auth.yaml

And finally set the decryption secret in the Flux Kustomization to sops-age.

Encrypting secrets using HashiCorp Vault

HashiCorp Vault is an identity-based secrets and encryption management system.

Encrypting with HashiCorp Vault follows the same workflow as PGP & Age.

Export the VAULT_ADDR and VAULT_TOKEN environment variables to your shell, then use sops to encrypt a Kubernetes Secret (see HashiCorp Vault for more details on enabling the transit backend and sops).

Then use sops to encrypt a Kubernetes Secret:

export VAULT_ADDR=https://vault.example.com:8200
export VAULT_TOKEN=my-token
sops --hc-vault-transit $VAULT_ADDR/v1/sops/keys/my-encryption-key --encrypt \
--encrypted-regex '^(data|stringData)$' --in-place basic-auth.yaml

Create a secret the vault token, the key name must be sops.vault-token to be detected as a vault token:

echo $VAULT_TOKEN |
kubectl create secret generic sops-hcvault \
--namespace=flux-system \
--from-file=sops.vault-token=/dev/stdin

And finally set the decryption secret in the Flux Kustomization to sops-hcvault.

Encrypting secrets using various cloud providers

When using AWS/GCP KMS, you don’t have to include the gpg secretRef under spec.provider (you can skip the --decryption-secret flag when running flux create kustomization), instead you’ll have to bind an IAM Role with access to the KMS keys to the kustomize-controller service account of the flux-system namespace for kustomize-controller to be able to fetch keys from KMS.

AWS

See the SOPS guide to Encrypting Using AWS KMS.

See the AWS integrations docs for details on how to set up SOPS authentication for AWS KMS in kustomize-controller.

Azure

See the SOPS guide to Encrypting Using Azure Key Vault.

See the Azure integrations docs for details on how to set up SOPS authentication for Azure Key Vault in kustomize-controller.

GCP

See the SOPS guide to Encrypting Using Azure Key Vault.

See the GCP integrations docs for details on how to set up SOPS authentication for GCP KMS in kustomize-controller.

GitOps workflow

A cluster admin should create the Kubernetes secret with the PGP keys on each cluster and add the GitRepository/Kustomization manifests to the fleet repository.

Git repository manifest:

apiVersion: source.toolkit.fluxcd.io/v1
kind: GitRepository
metadata:
  name: my-secrets
  namespace: flux-system
spec:
  interval: 1m
  url: https://github.com/my-org/my-secrets

Kustomization manifest:

apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: my-secrets
  namespace: flux-system
spec:
  interval: 10m0s
  sourceRef:
    kind: GitRepository
    name: my-secrets
  path: ./
  prune: true
  decryption:
    provider: sops
    secretRef:
      name: sops-gpg

Assuming a team member wants to deploy an application that needs to connect to a database using a username and password, they’ll be doing the following:

• create a Kubernetes Secret manifest locally with the db credentials e.g. db-auth.yaml
• encrypt the secret data field with sops
• create a Kubernetes Deployment manifest for the app e.g. app-deployment.yaml
• add the Secret to the Deployment manifest as a volume mount or env var
• commit the manifests db-auth.yaml and app-deployment.yaml to a Git repository that’s being synced by the GitOps toolkit controllers

Once the manifests have been pushed to the Git repository, the following happens:

• source-controller pulls the changes from Git
• kustomize-controller loads the GPG keys from the sops-pgp secret
• kustomize-controller decrypts the Kubernetes secrets with SOPS and applies them on the cluster
• kubelet creates the pods and mounts the secret as a volume or env variable inside the app container

SOPS encrypted_regex conflict

If your resource is encrypted it will be decrypted right before apply, but it may happen, that your patches will bring fields that match SOPS’ encrypted_regex expression and SOPS will fail during the decryption. Let’s say we have a simple resource.

apiVersion: v1
kind: Pod
metadata:
  name: pod
spec:
  containers:
    - name: main
      image: nginx:stable-alpine
      env:
        - name: ENC[AES256_GCM,data:...
          value: ENC[AES256_GCM,data:...
      resources:
        limits:
          memory: 50Mi
          cpu: 50m
sops:
  ...
  encrypted_regex: ^env$ # There it is
  ...

This Pod has every env list encrypted since we have encrypted_regex set during SOPS encryption. But next we have a patch like this.

apiVersion: v1
kind: Pod
metadata:
  name: pod
spec:
  containers:
    - name: patched
      image: nginx:stable-alpine
      env:
        - name: MainEnvValueIsEncrypted
          value: but this one is not

And as a result you will have.

apiVersion: v1
kind: Pod
metadata:
  name: pod
spec:
  containers:
    - name: main
      image: nginx:stable-alpine
      env:
        - name: ENC[AES256_GCM,data:...
          value: ENC[AES256_GCM,data:...
      resources:
        limits:
          memory: 50Mi
          cpu: 50m
    - name: patched
      image: nginx:stable-alpine
      env:
        - name: MainEnvValueIsEncrypted
          value: but this one is not
sops:
  ...
  encrypted_regex: ^env$ # There it is
  ...

At this point, Flux will call SOPS to decrypt the file and SOPS will try to decrypt all env keys, but container patched has this list in a plain text. SOPS will fail here.