feat: introduce FlagService CRD with reconciliation

[skyerus]

POC

This is a WIP implementation of the FlagService OFEP.

This PR introduces a CRD named FlagService. The creation of a FlagService CR (in OFO's namespace) triggers its reconciliation loop which does the following (in OFO's namespace):

• Creates a Deployment of flagd
• Creates a Service exposing the flagd deployment

How to run the POC

The demo aims to exemplify a legitimate end-to-end deployment scenario by using Kubernetes Gateway API (KGA) to ingest traffic to a demo application & the created flagd Service/Deployment.

Prerequisites:

• Kind
• Checkout OFO at this branch
• istioctl (this can be substituted for any other KGA implementor but make sure to replace references to istio with the substitute)

Note: To get this to work locally I had to add hostnames to my hosts file to route them to localhost. Without this the browser doesn't send the appropriate Host header to the Gateway, preventing it from being able to route the request.

# build OFO
IMG=ghcr.io/open-feature/open-feature-operator:local ARCH=arm64 make docker-build
# create kind cluster
kind create cluster --config ./test/e2e/kind-cluster.yml
# load OFO into cluster
kind load docker-image ghcr.io/open-feature/open-feature-operator:local
# deploy OFO
IMG=ghcr.io/open-feature/open-feature-operator:local make deploy-operator
# install KGA CRDs
kubectl apply -f https://github.com/kubernetes-sigs/gateway-api/releases/download/v0.6.2/standard-install.yaml
# install istio gateway
istioctl install --set profile=minimal -y
# deploy resources
kubectl apply -f config/samples/dev.yaml
# add hostnames to hosts file (location of hosts file is macOS specific in this example)
sudo sh -c 'echo "127.0.0.1 ofoclientapp.com" >> /private/etc/hosts'
sudo sh -c 'echo "127.0.0.1 flagd.ofoclientapp.com" >> /private/etc/hosts'
# port forward 8080 to the gateway pod
kubectl port-forward $(kubectl get pods --selector=istio.io/gateway-name=clientsidegateway -o \
  jsonpath='{.items[*].metadata.name}') 8080:80

Go to http://ofoclientapp.com:8080/ in your browser and click the Update color button to verify that the traffic is routed to flagd correctly.

Further Steps

• Handle update/delete of FlagService
• Create ServiceSpec/DeploymentSpec fields in FlagService to passthrough configuration
• Validation webhook to ensure FlagService is created in OFO's namespace
• Use configured OFO namespace (currently hardcoded)
• Testing
• Documentation (including examples of how to use FlagService in conjunction with KGA/Ingress to route traffic to flagd)

Related Issues

#371

Notes

Follow-up Tasks

How to test

[codecov]

Codecov Report

Merging #417 (7ac9376) into main (29d7cf0) will decrease coverage by 1.13%.
The diff coverage is 88.23%.

@@            Coverage Diff             @@
##             main     #417      +/-   ##
==========================================
- Coverage   78.12%   77.00%   -1.13%     
==========================================
  Files          12       12              
  Lines         855      687     -168     
==========================================
- Hits          668      529     -139     
+ Misses        153      131      -22     
+ Partials       34       27       -7     

Impacted Files	Coverage Δ
webhooks/pod_webhook.go	84.27% <86.66%> (+0.65%)	⬆️
webhooks/pod_webhook_deprecated.go	47.61% <100.00%> (ø)

Flag	Coverage Δ
component-tests	78.99% <88.23%> (-1.30%)	⬇️
unit-tests	45.12% <0.00%> (+8.86%)	⬆️

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