krm-fn-sealedsecrets

Usage

Two KRM functions are provided. One for sealing (encrypting) secrets and another for unsealing (decrypting) them.

Unsealing secrets should be considered a debugging or disaster-recovery action that should rarely need to be performed. It relies on having access to the SealedSecret controller private keys, and as such it should (and can) only be done by cluster-admins who have full access to the K8s API server. You should also be very careful not to accidently leak these keys.

Sealing secrets on the other hand can be done by anyone.

The API is a limited subset of the kubeseal CLI with some added features.

Seal

To seal secrets, use the ghcr.io/jashandeep-sohi/krm-fn-sealedsecrets/seal function image.

It takes a list of v1.Secrets and generates SealedSecrets for each of them. Configure it using this ConfigMap.

KPT

It can be used both imperatively and declaratively with KPT.

For example, given a bunch of Secrets:

cat <<EOF > secret-a.yaml
apiVersion: v1
kind: Secret
metadata:
  name: secret-a
  namespace: test
stringData:
  SOMETHING: "VERY SECRET"
EOF

cat <<EOF > secret-b.yaml
apiVersion: v1
kind: Secret
metadata:
  name: secret-b
  namespace: test
stringData:
  SOMETHING_ELSE: "ALSO SECRET"
EOF

To seal them, run:

kpt fn eval --image ghcr.io/jashandeep-sohi/krm-fn-sealedsecrets/seal:latest -- "cert=$(kubeseal --fetch-cert)"

This will generate a SealedSecret for each of them and write it to the same file as the original Secret.

The original Secret is also left in-place by default, but you should remove it as soon as possible to avoid leaking it (e.g. checking it into Git).

To do that, run the function with prune=true:

kpt fn eval --image ghcr.io/jashandeep-sohi/krm-fn-sealedsecrets/seal:latest -- "cert=$(kubeseal --fetch-cert)" prune=true

Here, we're fetching the certificate using kubeseal via a shell command substituion (kubeseal --fetch-cert), but it could come from anywhere (e.g. a local file).

This certificate is safe to check into Git, but keep in mind that the controller generates new ones periodically, so you should always use the latest one.

You can also store the function config in a file:

cat <<EOF > fn-config.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: does-not-matter
  annotations:
    config.kubernetes.io/local-config: "true"
data:
  prune: "true"
  cert: |-
    -----BEGIN CERTIFICATE-----
    MIIFazCCA1OgAwIBAgIUAZIki4fTKG4CPdFjcr+WOTPcZDwwDQYJKoZIhvcNAQEL
    BQAwRTELMAkGA1UEBhMCQVUxEzARBgNVBAgMClNvbWUtU3RhdGUxITAfBgNVBAoM
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    4E78/hmJY7BAPbXBFX0CIauBd3OZiPAfrmgcYCQdWhjdM5QgkD/DiKENOA8Si+2g
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    itwoyXW+ENj8/acRjmLU32dsBOtfEUHOFXnkvoahEGQqvUrOt+s9SJUjwwt4v8ps
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    Nj7Wa3vwV8vMj9t6LUmQWquAjY1hKWiTjywSfDfNgZjqiVwIusyqfk2ceeqCWeQ=
    -----END CERTIFICATE-----
EOF

And pass it to the function with:

kpt fn eval --image ghcr.io/jashandeep-sohi/krm-fn-sealedsecrets/seal:latest --fn-config fn-config.yaml

Kustomize

Kustomize also supports running KRM functions:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - ./secret-a.yaml
  - ./secret-b.yaml

transformers:
  - |-
    apiVersion: v1
    kind: ConfigMap
    metadata:
      name: does-not-matter
      annotations:
        config.kubernetes.io/function: |
          container:
            image: ghcr.io/jashandeep-sohi/krm-fn-sealedsecrets/seal:latest
    data:
      prune: "true"
      cert: |-
        -----BEGIN CERTIFICATE-----
        MIIFazCCA1OgAwIBAgIUAZIki4fTKG4CPdFjcr+WOTPcZDwwDQYJKoZIhvcNAQEL
        BQAwRTELMAkGA1UEBhMCQVUxEzARBgNVBAgMClNvbWUtU3RhdGUxITAfBgNVBAoM
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        LCw/X7btQH45FmtxlVUUpdT97vW39y+t5BjlCcRkPsyE5oEm/KW5tNP3HseqyhL2
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        Nj7Wa3vwV8vMj9t6LUmQWquAjY1hKWiTjywSfDfNgZjqiVwIusyqfk2ceeqCWeQ=
        -----END CERTIFICATE-----

And then run:

kustomize build --enable-alpha-plugins

Name Suffx Hash

You can suffix a hash to the name (that's dependent on the secret data) with nameSuffixHash=true:

kpt fn eval --image ghcr.io/jashandeep-sohi/krm-fn-sealedsecrets/seal:latest -- "cert=$(kubeseal --fetch-cert)" nameSuffixHash=t

Kustomize Stub Secrets

When using Kustomize, you might have some references to Secrets in other resources (e.g. Pod.spec.containers.envFrom.secretsRef.name) that'd you'd like to be updated when the name changes because of nameSuffixHash=true.

You can do that by emmiting stub v1.Secrets along with the SealedSecret:

kpt fn eval --image ghcr.io/jashandeep-sohi/krm-fn-sealedsecrets/seal:latest -- "cert=$(kubeseal --fetch-cert)" nameSuffixHash=t emmitKustomizeStubSecrets=t

Checkout a more complete example.

Note: This is a hack that relies on annotations that are internal to Kustomize. There is no guarntee this will work with all version of Kustomize and may break at any time.

Name Reference Kustomization

If you'd rather not rely on "internal" Kustomize annotation APIs that could break at anytime, you can also get name references to work by using the nameRefKustomizationDir option.

When provided, this will generate a Kustomization to that directory that can be sourced by other Kustomizations to patch any name references:

kpt fn eval --image ghcr.io/jashandeep-sohi/krm-fn-sealedsecrets/seal:latest -- "cert=$(kubeseal --fetch-cert)" nameSuffixHash=t nameRefKustomizationDir=fix-secret-refs

See this for a practical example.

Unseal

To unseal SealedSecrets, use the ghcr.io/jashandeep-sohi/krm-fn-sealedsecrets/unseal function image.

It takes in a list of SealedSecrets and generates v1.SealedSecret for each of them. Configure it using this ConfigMap.

For example, with KPT you can run (subtitute <controller-name> with the namespace that sealed-secrets controller is running in):

kpt fn eval --image ghcr.io/jashandeep-sohi/krm-fn-sealedsecrets/unseal:latest -- "controllerPrivateKeys=$(kubectl -n <controller-namespace> get secret -l 'sealedsecrets.bitnami.com/sealed-secrets-key' -o yaml)"

Unsealed v1.Secrets do not clobber over any preexiting v1.Secrets with the same name/namespace, so in some rare cases you might end up with duplicates, but Secrets generated by this function do have a krm-fn-sealedsecrets.io/unsealed=true annotation set if you'd like to filter them out.

KPT Exec Nix

You can also run these functions locally with Nix (i.e. without any of the restrictions & sandboxing that containers provide):

kpt fn eval --exec 'nix run github:jashandeep-sohi/krm-fn-sealedsecrets#seal' ...

See ./examples/exec-nix-seal/ on how to do it declaratively.

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