Add support for nginx ingress controller

[stefanprodan]

This PR adds support for nginx ingress controller canary deployments.

How to test this:

Clone this repo and checkout the nginx branch:

git clone https://github.com/weaveworks/flagger
cd flagger
git checkout nginx

Install the nginx ingress controller with Helm:

helm upgrade -i nginx stable/nginx-ingress \
--namespace ingress-nginx \
--set controller.stats.enabled=true \
--set controller.metrics.enabled=true

Install Prometheus:

kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/master/deploy/monitoring/configuration.yaml

kubectl create -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/master/deploy/monitoring/prometheus.yaml

Install Flagger with nginx support:

helm repo add flagger https://flagger.app

helm upgrade -i flagger flagger/flagger \
--namespace ingress-nginx \
--set metricsServer=http://prometheus-server:9090 \
--set meshProvider=nginx \
--set image.tag=nginx-a233b99

Install the load tester:

helm upgrade -i flagger-loadtester flagger/loadtester \
--namespace test

Edit ./artifacts/nginx/ingress and ./artifacts/nginx/canary and replace app.example.com with your own domain.

Deploy the podinfo in the test namespace:

kubectl apply -f ./artifacts/nginx

Check initialisation:

 kubectl get canaries --all-namespaces

Trigger canary deployment:

kubectl -n test set image deployment/podinfo \
podinfod=quay.io/stefanprodan/podinfo:1.4.1

Check deployment:

watch kubectl -n test describe canary/podinfo

Generate 500 errors:

hey -z 2m -c 5 -q 5 http://app.example.com/status/500

Trigger canary deployment:

kubectl -n test set image deployment/podinfo \
podinfod=quay.io/stefanprodan/podinfo:1.4.2

Verify rollback:

kubectl -n ingress-nginx logs deploy/flagger -f | jq .msg

Fix: #169