GitOps using FluxCD (v2)

FluxCD is a GitOps operator for Kubernetes. It synchronizes the status of the cluster from manifests allocated in different repositories (Git or Helm). This approach fits perfectly with External Secrets on clusters which are dynamically created, to get credentials with no manual intervention from the beginning.

Advantages

This approach has several advantages as follows:

Homogenize environments allowing developers to use the same toolset in Kind in the same way they do in the cloud provider distributions such as EKS or GKE. This accelerates the development
Reduce security risks, because credentials can be easily obtained, so temptation to store them locally is reduced.
Application compatibility increase: Applications are deployed in different ways, and sometimes they need to share credentials. This can be done using External Secrets as a wire for them at real time.
Automation by default oh, come on!

The approach

FluxCD is composed by several controllers dedicated to manage different custom resources. The most important ones are Kustomization (to clarify, Flux one, not Kubernetes' one) and HelmRelease to deploy using the approaches of the same names.

External Secrets can be deployed using Helm as explained here. The deployment includes the CRDs if enabled on the values.yaml, but after this, you need to deploy some SecretStore to start getting credentials from your secrets manager with External Secrets.

The idea of this guide is to deploy the whole stack, using flux, needed by developers not to worry about the credentials, but only about the application and its code.

The problem

This can sound easy, but External Secrets is deployed using Helm, which is managed by the HelmController, and your custom resources, for example a ClusterSecretStore and the related Secret, are often deployed using a kustomization.yaml, which is deployed by the KustomizeController.

Both controllers manage the resources independently, at different moments, with no possibility to wait each other. This means that we have a wonderful race condition where sometimes the CRs (SecretStore,ClusterSecretStore...) tries to be deployed before than the CRDs needed to recognize them.

The solution

Let's see the conditions to start working on a solution:

The External Secrets operator is deployed with Helm, and admits disabling the CRDs deployment
The race condition only affects the deployment of CustomResourceDefinition and the CRs needed later
CRDs can be deployed directly from the Git repository of the project using a Flux Kustomization
Required CRs can be deployed using a Flux Kustomization too, allowing dependency between CRDs and CRs
All previous manifests can be applied with a Kubernetes kustomization

Create the main kustomization

To have a better view of things needed later, the first manifest to be created is the kustomization.yaml

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

resources:
# Deploy the Vault access secret
- namespace.yaml
- secret-token.yaml

# Deploy the repositories
- repositories.yaml

# Deploy the CRDs
- deployment-crds.yaml

# Deploy the operator
- deployment.yaml

# Deploy default Custom Resources from 'crs' directory
# INFO: This depends on the CRDs deployment. Will happen after it
- deployment-crs.yaml

Create the secret

To access your secret manager, External Secrets needs some credentials. They are stored inside a Secret, which is intended to be deployed by automation as a good practise. This time, a placeholder called secret-token.yaml is show as an example:

# The namespace.yaml first
apiVersion: v1
kind: Namespace
metadata:
  name: external-secrets

apiVersion: v1
kind: Secret
metadata:
  name: vault-token-global
  namespace: external-secrets
stringData:
  # This token must be patched by overlays. Not here for security reasons
  token: change-me-placeholder

Creating the references to repositories

Create a manifest called repositories.yaml to store the references to external repositories for Flux

# Reference to Helm repository
apiVersion: source.toolkit.fluxcd.io/v1
kind: HelmRepository
metadata:
  name: external-secrets
  namespace: flux-system
spec:
  interval: 10m
  url: https://charts.external-secrets.io
---
apiVersion: source.toolkit.fluxcd.io/v1
kind: GitRepository
metadata:
  name: external-secrets
  namespace: flux-system
spec:
  interval: 10m
  ref:
    tag: v0.10.3
  url: http://github.com/external-secrets/external-secrets

Deploy the CRDs

As mentioned, CRDs can be deployed using the official Helm package, but to solve the race condition, they will be deployed from our git repository using a Kustomization manifest called deployment-crds.yaml as follows:

---
apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: external-secrets-crds
  namespace: flux-system
spec:
  interval: 10m
  path: ./deploy/crds
  prune: true
  sourceRef:
    kind: GitRepository
    name: external-secrets

Deploy the operator

The operator is deployed using a HelmRelease manifest to deploy the Helm package, but due to the special race condition, the deployment must be disabled in the values of the manifest called deployment.yaml, as follows:

# How to manage values files. Ref: https://fluxcd.io/docs/guides/helmreleases/#refer-to-values-inside-the-chart
# How to inject values: https://fluxcd.io/docs/guides/helmreleases/#cloud-storage
---
apiVersion: helm.toolkit.fluxcd.io/v2
kind: HelmRelease
metadata:
  name: external-secrets
  namespace: flux-system
spec:
  # Override Release name to avoid the pattern Namespace-Release
  # Ref: https://fluxcd.io/flux/components/helm/api/v2/#helm.toolkit.fluxcd.io/v2.HelmRelease
  releaseName: external-secrets
  targetNamespace: external-secrets
  interval: 10m
  chart:
    spec:
      chart: external-secrets
      version: 0.10.3
      sourceRef:
        kind: HelmRepository
        name: external-secrets
        namespace: flux-system
  values:
    installCRDs: false

  # Ref: https://fluxcd.io/flux/components/helm/api/v2/#helm.toolkit.fluxcd.io/v2.Install
  install:
    createNamespace: true

Deploy the CRs

Now, be ready for the arcane magic. Create a Kustomization manifest called deployment-crs.yaml with the following content:

---
apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: external-secrets-crs
  namespace: flux-system
spec:
  dependsOn:
    - name: external-secrets-crds
  interval: 10m
  path: ./infrastructure/external-secrets/crs
  prune: true
  sourceRef:
    kind: GitRepository
    name: flux-system

There are several interesting details to see here, that finally solves the race condition:

First one is the field dependsOn, which points to a previous Kustomization called external-secrets-crds. This dependency forces this deployment to wait for the other to be ready, before start being deployed.
The reference to the place where to find the CRs
```
path: ./infrastructure/external-secrets/crs
sourceRef:
 kind: GitRepository
 name: flux-system
```
Custom Resources will be searched in the relative path ./infrastructure/external-secrets/crs of the GitRepository called flux-system, which is a reference to the same repository that FluxCD watches to synchronize the cluster. With fewer words, a reference to itself, but going to another directory called crs

Of course, allocate inside the mentioned path ./infrastructure/external-secrets/crs, all the desired CRs to be deployed, for example, a manifest clusterSecretStore.yaml to reach your Hashicorp Vault as follows:

apiVersion: external-secrets.io/v1beta1
kind: ClusterSecretStore
metadata:
  name: vault-backend-global
spec:
  provider:
    vault:
      server: "https://vault.your-domain.com"
      path: secret
      version: v2
      auth:
        # points to a secret that contains a vault token
        # https://www.vaultproject.io/docs/auth/token
        tokenSecretRef:
          name: "vault-token-global"
          key: "token"
          namespace: external-secrets

Results

At the end, the required files tree is shown in the following picture:

FluxCD files tree