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Secure your secrets with Sealed Secrets

September 25, 2021 - By: Thomas Jungbauer ( Lastmod: 2021-09-25 ) - 3 min read

Working with a GitOps approach is a good way to keep all configurations and settings versioned and in sync on Git. Sensitive data, such as passwords to a database connection, will quickly come around. Obviously, it is not a idea to store clear text strings in a, maybe even public, Git repository. Therefore, all sensitive information should be stored in a secret object. The problem with secrets in Kubernetes is that they are actually not encrypted. Instead, strings are base64 encoded which can be decoded as well. Thats not good … it should not be possible to decrypt secured data. Sealed Secret will help here…

Sealed Secrets by Bitnami[1] is one option to create real, encrypted secrets. It contains two parts:

A cluster-side controller / operator, which decrypts the secrets server-side on OpenShift installed in a dedicated namespace usually called sealed secrets.
kubeseal - a client-side command line tool

Prerequisites

An OpenShift 4 cluster with cluster-admin permissions.

Sealed Secrets Operator

Goto OperatorHub and search for Sealed Secrets (This is a Community Operator)

Figure 1. Search Sealed Secrets in OperatorHub

Install the operator, using the default settings, into the namespace sealed-secrets

Figure 2. Installed Sealed Secret Operator

Install the CRD SealedSecretController

Install the following object. For now the default values can be used.

apiVersion: bitnami.com/v1alpha1
kind: SealedSecretController
metadata:
  name: controller (1)
  namespace: sealed-secrets
spec:
  networkPolicy: false
  nodeSelector: {}
  podLabels: {}
  resources: {}
  affinity: {}
  securityContext:
    fsGroup: ''
    runAsUser: ''
  rbac:
    create: true
    pspEnabled: false
  crd:
    create: true
    keep: true
  ingress:
    annotations: {}
    enabled: false
    hosts:
      - chart-example.local
    path: /v1/cert.pem
    tls: []
  serviceAccount:
    create: true
    name: ''
  image:
    pullPolicy: IfNotPresent
    repository: >-
      quay.io/bitnami/sealed-secrets-controller@sha256:8e9a37bb2e1a6f3a8bee949e3af0e9dab0d7dca618f1a63048dc541b5d554985
  secretName: sealed-secrets-key
  tolerations: []
  controller:
    create: true
  priorityClassName: ''
  podAnnotations: {}

1	Be aware of the name of the controller OBJECT (name: controller). It is used lated as part of the actual controller name

Install the command line tool kubeseal

The kubeseal binary can be easily installed using either

on Mac: brew install kubeseal or

on Linux:

wget https://github.com/bitnami-labs/sealed-secrets/releases/download/v0.16.0/kubeseal-linux-amd64 -O kubeseal

install -m 755 kubeseal /usr/local/bin/

Testing Sealed Secrets

Create a new project oc new-project myproject

Create a secret

echo -n "my_super_secret_string" \
    | kubectl create secret generic mypasswords --dry-run=client --from-file=password=/dev/stdin -o json \
    | kubeseal --controller-namespace=sealed-secrets --controller-name=controller-sealed-secrets --format json > mysealedsecret.json (1)

1	The switches --controller-namespace define the namespace where the operator is installed, --controller-name is a combination of the SealedSecretController object name and the name of the namespace

The password=my_super_secret_string is created and piped into kubeseal which is using the controller, where the server created a certificate for encryption, to create an encrypted json file mysealedsecret.json. It is important to note, that the actually Kubernetes secret object is not created at this stage.

The file mysealedsecret.json is encrypted now and it is safe to store this file on Github.

It looks like this:

{
  "kind": "SealedSecret",
  "apiVersion": "bitnami.com/v1alpha1",
  "metadata": {
    "name": "mypasswords",
    "namespace": "myproject", (1)
    "creationTimestamp": null
  },
  "spec": {
    "template": {
      "metadata": {
        "name": "mypasswords",
        "namespace": "myproject", (1)
        "creationTimestamp": null
      },
      "data": null
    },
    "encryptedData": {
      "password": "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"
    }
  }
}

1	The sealed secret will be created in your project

Upload the sealed secret oc create -f mysealedsecret.json

Verify Secret

The object SealedSecret is created:

oc get SealedSecret

NAME          AGE
mypasswords   3s

The SealedSecretController will decrypt the and store the secret in the namespace. This can take a few seconds:

oc get secret mypasswords

NAME          TYPE     DATA   AGE
mypasswords   Opaque   1      25s

Extract the secret and verify that your string has been stored as "normal" secret

oc extract secret/mypasswords --to=-

# password
my_super_secret_string

Updating or appending new values

The process for updateing or appending a secret is similar. The only difference is that a new value for the key string is new.

# Updaing string
echo -n "my_NEW_super_secret_string" \
    | kubectl create secret generic mypasswords --dry-run=client --from-file=password=/dev/stdin -o json \
    | kubeseal --controller-namespace=sealed-secrets --controller-name=controller-sealed-secrets --format json --merge-into mysealedsecret.json

# Appending
echo -n "my_appended_string" \
    | kubectl create secret generic mypasswords --dry-run=client --from-file=appendedstring=/dev/stdin -o json \
    | kubeseal --controller-namespace=sealed-secrets --controller-name=controller-sealed-secrets --format json --merge-into mysealedsecret.json

Be sure that you are in the namespace you want to install the secret

Upload the sealed secret oc apply -f mysealedsecret.json and extract it again to validate:

oc extract secret/mypasswords --to=-

# appendedstring
my_appended_string
# password
my_NEW_super_secret_string

Sources

[1]: Bitname Readme on Github

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