haskell-example-operator

{ConfigMap|CRD}-based approach for managing the X in Kubernetes and OpenShift.

This operator uses abstract-operator library.

Info

Very simple operator that calls Haskell code (from Groovy), prints the Nth Fibonacci number (counting from zero) to console and also creates a config map with the result. So it demonstrates the async workload in Kubernetes.

The skeleton of the application is written in Groovy, because Frege currently doesn't support extending existing Java classes. However, the operator calls the haskell pure function in the onAdd method. For demonstration purposes we created very simple haskell code that calculates the Nth fib number, it also demonstrates the lazy evaluation on infinite data structures called from a language that doesn't have such features:

module acme.Fibonacci where

fibs a b = a : fibs b (a + b)
fibonacci = fibs 0L 1L

fib :: Long -> Long
fib n = head $ drop (Long.int n) $ fibonacci

(source)

Example

cat <<EOF | kubectl apply -f -
apiVersion: io.acme/v1
kind: fibonacciinput
metadata:
  name: fourty-second-fib
spec:
  input: 42
EOF

meanwhile in the K8s log:

...
2018-12-03 15:53:05 INFO  AbstractOperator:? - new input has been created: io.operator.types.FibonacciInput@59c12e28[name=fourty-second-fib,input=42,additionalProperties={}]
the 42th fibonacci number is: 267914296
...

Also the corresponding config map with the result (called the same way as the input CM with -result sufix) was created:

kubectl describe cm fourty-second-fib-result

Name:		fourty-second-fib-result
Namespace:	myproject
Labels:		<none>
Annotations:	<none>

Data
====
result:
----
267914296

Build

make build

Quick Start

Run the haskell-example-operator deployment:

kubectl apply -f manifest/operator.yaml

Create new ConfigMap from the prepared example:

kubectl apply -f examples/cm.yaml

For deployment on OpenShift use the same commands as above, but with oc instead of kubectl.

This operator can also work with CRDs. Assuming the admin user is logged in, you can install the operator with:

kubectl apply -f manifest/operator-crd.yaml

and then create the Spark clusters by creating the custom resources (CR).

kubectl apply -f examples/cr.yaml

Development

make devel

This will build the image and deploys the operator into OpenShift. It assumes the oc on PATH.