GitOps Driven Configuration of OCM Applications

Introduction#

This guide is the final part of our series exploring OCM, the ocm-controller, and how to drive GitOps processes using OCM as the source of truth.

Check out the previous guides if you haven’t already:

• Deploy Applications with OCM & GitOps
• Air-gapped GitOps with OCM & Flux

In this guide we will pick-up where we left off in the air-gapped example.

We have successfully transferred a component to our private environment and deployed it using the ocm-controller. However, the Kubernetes Deployment for podinfo is failing because it does not have permission to access our private container images.

Let’s fix that.

Table of Contents#

• Introduction
• Table of Contents
• Requirements
  • Component Content Recap
  • GitOps & Configuration
  • Verify Deployment
  • Conclusion

Requirements#

• OCM command line tool
• kubectl
• git
• gh
• kind
• flux

Component Content Recap#

We saw previously that the podinfo component contains three resources:

• podinfo container image
• kubernetes deployment manifest for podinfo
• configuration file read by the ocm-controller

We can list these resources using the ocm CLI:

ocm get resources ghcr.io/phoban01//phoban.io/podinfo -c v6.3.5

NAME       VERSION IDENTITY TYPE      RELATION
config     6.3.5            PlainText local
deployment 6.3.5            Directory local
image      6.3.5            ociImage  external

Let’s examine the config resource once again and this time focus on a section named configuration:

ocm download resource ghcr.io/phoban01//phoban.io/podinfo -c v6.3.5 config -O -

apiVersion: config.ocm.software/v1alpha1
kind: ConfigData
metadata:
  name: ocm-config
configuration:
  defaults:
    serviceAccountName: default # this is the default value for our variable
  rules:
  - value: (( serviceAccountName ))  # this variable
    file: deployment.yaml # will be inserted into this file
    path: spec.template.spec.serviceAccountName # at this path
  schema: # allows us to define constraints for configuration values
    type: object
    additionalProperties: false
    properties:
      serviceAccountName:
        type: string
...

The configuration section contains a set of rules, some default values, and a schema.

These can be used to provide configuration values, which will be inserted into our resources at runtime by the ocm-controller.

In the above resource we can see that there is a variable named serviceAccountName and a rule which specifies that this variable should be inserted into the path spec.template.spec.serviceAccountName in the deployment.yaml file.

GitOps & Configuration#

Similar to how we Localized our deployment resource in the previous guide, we create another Custom Resource with the type Configuration in order to apply our configuration rules:

cat > ./components/localization.yaml >>EOF
apiVersion: delivery.ocm.software/v1alpha1
kind: Configuration
metadata:
  name: podinfo-deployment
  namespace: ocm-system
spec:
  interval: 1m
  sourceRef:
    kind: Localization
    name: podinfo-deployment # this is the podinfo deployment localization
  configRef:
    kind: ComponentVersion
    name: podinfo
    resourceRef:
      name: config # here we reference the configuration resource
  values:
    serviceAccountName: app-ops
EOF

You can see that this time we have used the Localization resource as the input for the Configuration and have provided the configuration rules using the spec.configRef field. Finally, we specify our service account name in the spec.values.serviceAccountName field.

Once again we need to update the FluxDeployer so that it consumes the Configuration rather than the Localization:

apiVersion: delivery.ocm.software/v1alpha1
kind: FluxDeployer
metadata:
  name: podinfo
  namespace: ocm-system
spec:
  sourceRef:
    kind: Configuration
    name: podinfo-deployment
  kustomizationTemplate:
    interval: 1m0s
    path: ./
    prune: true
    targetNamespace: default

Before we push these changes, we need to actually create the ServiceAccount and image-pull Secret in the target namespace.

Let’s create the secret as we did previously (Note that in a real world scenario there are a number of ways to manage secrets when doing Gitops):

kubectl create secret docker-registry -n default ghcr-cred \
  --docker-server=ghcr.io \
  --docker-username=$GITHUB_USER \
  --docker-password=$GITHUB_TOKEN

Now let’s add the ServiceAccount:

cat > ./clusters/kind/service_account.yaml <<EOF

apiVersion: v1
kind: ServiceAccount
metadata:
  name: app-ops
  namespace: default
imagePullSecrets:
- name: ghcr-cred

Finally we are ready commit, push, and reconcile these changes:

git add ./components ./clusters

git commit -m "move to air-gapped repository"

git push

flux reconcile source git flux-system

Verify Deployment#

Flux should now be reconciling the Configured manifest with image references pointing to our private OCM repository and the correct ServiceAccount configured.

We can verify this using kubectl:

kubectl get deployment -n default podinfo -oyaml | grep serviceAccountName | xargs

serviceAccountName: app-ops

kubectl get deployment -n default podinfo -oyaml | grep image | xargs

image: ghcr.io/phoban01/air-gapped/stefanprodan/podinfo:6.3.5

Kubernetes can now retrieve the image and all pods should be happily running.

Conclusion#

We have shown how OCM and Flux can be combined to configure applications at runtime.

GitOps driven configuration in tandem with the powerful Localization functionality provided by OCM offers tremendous flexibility, reliability, and scalability when deploying your applications to any kind of compute environment, be it public, private or edge.