Support for Jsonnet

What is JSONNET

jsonnet is a data templating language and configuration file format designed to simplify the creation and management of complex JSON or YAML data structures. It provides a concise and flexible syntax for generating JSON-like data by defining reusable templates, composing objects and arrays, and applying transformations.

If you want to use jsonnet in conjunction with Sveltos, you can install the jsonnet controller by performing the below:

$ kubectl apply -f https://raw.githubusercontent.com/gianlucam76/jsonnet-controller/main/manifest/manifest.yaml

The above command will install the necessary components for jsonnet controller.

The jsonnet controller offers the capability to process jsonnet files using different sources, such as Flux Sources (GitRepository/OCIRepository/Bucket), ConfigMap, or Secrets. It then programmatically invokes jsonnet go module and stores the output in the Status section making it available for Sveltos to consume.

Option 1: GitRepository

We can leverage GitRepository as a source for the jsonnet controller². For example, in the provided GitHub repository jsonnet-examples, we can find the jsonnet files that Flux will sync.

To instruct the jsonnet controller to fetch files from this repository, create a JsonnetSource CRD instance with the below configuration:

apiVersion: extension.projectsveltos.io/v1alpha1
kind: JsonnetSource
metadata:
  name: jsonnetsource-flux
spec:
  namespace: flux-system
  name: flux-system
  kind: GitRepository
  path: ./variables/deployment.jsonnet
  variables:
    deploymentName: eng
    namespace: staging
    replicas: "3"

The path field specifies the location within the Git repository where the jsonnet file is stored. Once Flux detects changes in the repository and syncs it, the jsonnet-controller will automatically invoke the jsonnet module and store the output in the Status section of the JsonnetSource instance.

At this point, you can use the Sveltos' template feature to deploy the output of the jsonnet (Kubernetes resources) to a managed cluster. The Kubernetes add-on controller will take care of deploying it¹.

ClusterProfile

apiVersion: config.projectsveltos.io/v1alpha1
kind: ClusterProfile
metadata:
  name: deploy-resources
spec:
  clusterSelector: env=fv
  templateResourceRefs:
  - resource:
      apiVersion: extension.projectsveltos.io/v1alpha1
      kind: JsonnetSource
      name: jsonnetsource-flux
      namespace: default
    identifier: JsonnetSource
  policyRefs:
  - kind: ConfigMap
    name: jsonnet-resources
    namespace: default
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: jsonnet-resources
  namespace: default
  annotations:
    projectsveltos.io/template: "true"  # add annotation to indicate Sveltos content is a template
data:
  resource.yaml: |
    {{ (index .MgmtResources "JsonnetSource").status.resources }}

The above configuration instructs Sveltos to deploy the resources generated by jsonnet to the selected managed clusters.

$ sveltosctl show addons 
+-------------------------------------+-----------------+-----------+------+---------+-------------------------------+------------------+
|               CLUSTER               |  RESOURCE TYPE  | NAMESPACE | NAME | VERSION |             TIME              | CLUSTER PROFILES |
+-------------------------------------+-----------------+-----------+------+---------+-------------------------------+------------------+
| default/sveltos-management-workload | apps:Deployment | staging   | eng  | N/A     | 2023-05-26 00:24:57 -0700 PDT | deploy-resources |
+-------------------------------------+-----------------+-----------+------+---------+-------------------------------+------------------+

Option 2: ConfigMap/Secret

Alternatively, you can use a ConfigMap/Secret as a source for the jsonnet controller

Step 1: Create a tarball containing the jsonnet files

$ tar -czf jsonnet.tar.gz -C ~mgianluc/go/src/github.com/gianlucam76/jsonnet-examples/multiple-files .

Step 2: Create a ConfigMap with the tarball

$ kubectl create configmap jsonnet --from-file=jsonnet.tar.gz=jsonnet.tar.gz

Step 3: Create a JsonnetSource instance that references this ConfigMap

apiVersion: extension.projectsveltos.io/v1alpha1
kind: JsonnetSource
metadata:
  name: jsonnetsource-configmap
spec:
  namespace: default
  name: jsonnet
  kind: ConfigMap
  path: ./main.jsonnet
  variables:
    namespace: production

Outcome will be same as seen above with Flux GitRepository:

apiVersion: extension.projectsveltos.io/v1alpha1
kind: JsonnetSource
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"extension.projectsveltos.io/v1alpha1","kind":"JsonnetSource","metadata":{"annotations":{},"name":"jsonnetsource-configmap","namespace":"default"},"spec":{"kind":"ConfigMap","name":"jsonnet","namespace":"default","path":"./main.jsonnet","variables":{"namespace":"production"}}}
  creationTimestamp: "2023-05-26T08:28:48Z"
  generation: 1
  name: jsonnetsource-configmap
  namespace: default
  resourceVersion: "121599"
  uid: eea93390-771d-4176-92fe-2b761b803764
spec:
  kind: ConfigMap
  name: jsonnet
  namespace: default
  path: ./main.jsonnet
  variables:
    namespace: production
status:
  resources: |
    ---
    {"apiVersion":"apps/v1","kind":"Deployment","metadata":{"name":"my-deployment","namespace":"production"},"spec":{"replicas":3,"selector":{"matchLabels":{"app":"my-app"}},"template":{"metadata":{"labels":{"app":"my-app"}},"spec":{"containers":[{"image":"my-image:latest","name":"my-container","ports":[{"containerPort":8080}]}]}}}}
    ---
    {"apiVersion":"v1","kind":"Service","metadata":{"name":"my-service","namespace":"production"},"spec":{"ports":[{"port":80,"protocol":"TCP","targetPort":8080}],"selector":{"app":"my-app"},"type":"LoadBalancer"}}

  apiVersion: source.toolkit.fluxcd.io/v1
  kind: GitRepository
  metadata:
    finalizers:
    - finalizers.fluxcd.io
    name: flux-system
    namespace: flux-system
  spec:
    interval: 1m0s
    ref:
      branch: main
    secretRef:
      name: flux-system
    timeout: 60s
    url: ssh://git@github.com/gianlucam76/jsonnet-examples

---

1. Instructing Sveltos involves the initial step of retrieving a resource from the management cluster, which is the JsonnetSource instance named jsonnetsource-flux in the default namespace. Sveltos is then responsible for deploying the resources found within the jsonnet-resources ConfigMap. However, this ConfigMap acts as a template, requiring instantiation before deployment. Within the Data section of the ConfigMap, there is a single entry called resource.yaml. After instantiation, this entry will contain the content that the jsonnet controller has stored in the JsonnetSource instance. ↩

2. Flux is present in the management cluster and it is used to sync from GitHub repository. The GitRepository instance is the below. ↩