Build and run a OPA policy for Kubewarden

In the previous section you wrote your Rego policy. The structure looks like:

.
├── data
│   ├── default-ns.json
│   └── other-ns.json
├── policy.rego
└── request.rego

1 directory, 4 files

Build

To build:

$ opa build -t wasm -e policy/main policy.rego request.rego

This builds the rego policy, with:

target: wasm. You want to build the policy for the wasm target.
entrypoint: policy/main. The entry point is the main rule inside the policy package.
policy.rego: Build and include the policy.rego file.
request.rego: Build and include the request.rego file.

After the build completes, opa build has generated a bundle.tar.gz file. You can extract it:

$ tar -xf bundle.tar.gz /policy.wasm

Now the tree looks like the following:

.
├── bundle.tar.gz
├── data
│   ├── default-ns.json
│   └── other-ns.json
├── policy.rego
├── policy.wasm
└── request.rego

1 directory, 6 file

You have your policy.wasm file:

$ file policy.wasm
policy.wasm: WebAssembly (wasm) binary module version 0x1 (MVP)

Now you run it.

Run

Use kwctl to run the policy:

$ kwctl run -e opa --request-path data/other-ns.json policy.wasm | jq
{
  "uid": "1299d386-525b-4032-98ae-1949f69f9cfc",
  "allowed": true
}

This request is accepted by the policy, since this is the request pointing to the other namespace.

execution-mode: opa. Rego policies can be targeting Open Policy Agent or Gatekeeper. You must tell kwctl what kind of policy you’re running.
request-path: The location of the recorded request that kwctl sends the policy to for evaluation.

Now try to evaluate the request that creates the pod inside the default namespace:

$ kwctl run -e opa --request-path data/default-ns.json policy.wasm | jq
{
  "uid": "1299d386-525b-4032-98ae-1949f69f9cfc",
  "allowed": false,
  "status": {
    "message": "it is forbidden to use the default namespace"
  }
}

The policy is rejecting the request, giving a reason back to the API server that’s returned to the user or API consumer.