Service and documentation for istio (mesh mode)

[muscionig]

closes #56

Changes

This PR adds documentation to run the autoscaler-keda extension with Istio injection.
@skonto I opened this on top of #81, that is why the set of changes is larger. Feel free to directly review only this PR.

Minor Changes

• 🎁 split development guidelines adding a specific section for Istio.
• 🎁 documented istio in mesh mode.
• 🎁 documented installation of prometheus in its own namespace (to facilitate mTLS setup with the documentation provided by Istio) and edits to the config-autoscaler-keda configmap to scrape metric from a specific prometheus address.

istio:

before scaling:

$ kubectl get po -A
NAMESPACE            NAME                                                     READY   STATUS    RESTARTS      AGE
cert-manager         cert-manager-67c98b89c8-gxvtb                            1/1     Running   0             35m
cert-manager         cert-manager-cainjector-5c5695d979-s6jbj                 1/1     Running   0             35m
cert-manager         cert-manager-webhook-7f9f8648b9-zd6jj                    1/1     Running   0             35m
istio-system         istio-ingressgateway-5f8bcfbff9-5cq27                    1/1     Running   0             34m
istio-system         istio-ingressgateway-5f8bcfbff9-lpcpv                    1/1     Running   0             34m
istio-system         istio-ingressgateway-5f8bcfbff9-wh486                    1/1     Running   0             34m
istio-system         istiod-85877f7d98-9gjr9                                  1/1     Running   0             34m
istio-system         istiod-85877f7d98-b87bg                                  1/1     Running   0             34m
istio-system         istiod-85877f7d98-cvchw                                  1/1     Running   0             34m
keda                 keda-admission-webhooks-685d94fcff-kjvlw                 1/1     Running   0             24m
keda                 keda-operator-65f5568c7b-9kbc8                           1/1     Running   1 (24m ago)   24m
keda                 keda-operator-metrics-apiserver-69c577c9cf-qxxhx         1/1     Running   0             24m
knative-serving      activator-5754bdb79d-9gpn5                               2/2     Running   0             34m
knative-serving      autoscaler-57d66f69d9-cmv6j                              2/2     Running   0             34m
knative-serving      autoscaler-keda-fc6b797b4-lvmss                          2/2     Running   0             21m
knative-serving      controller-f48959855-lhrwz                               2/2     Running   1 (34m ago)   34m
knative-serving      net-istio-controller-69858b66f7-qfnq8                    1/1     Running   0             34m
knative-serving      net-istio-webhook-5645569675-jvj2r                       2/2     Running   0             34m
knative-serving      webhook-778946f8-ftjps                                   2/2     Running   0             34m
kube-system          coredns-5dd5756b68-d92j4                                 1/1     Running   0             36m
kube-system          etcd-minikube                                            1/1     Running   0             36m
kube-system          kube-apiserver-minikube                                  1/1     Running   0             36m
kube-system          kube-controller-manager-minikube                         1/1     Running   0             36m
kube-system          kube-proxy-dczz8                                         1/1     Running   0             36m
kube-system          kube-scheduler-minikube                                  1/1     Running   0             36m
kube-system          storage-provisioner                                      1/1     Running   1 (36m ago)   36m
metrics-test-istio   metrics-test-istio-00001-deployment-7d57bbb8d8-86zsg     3/3     Running   0             14m
prometheus           alertmanager-prometheus-kube-prometheus-alertmanager-0   2/2     Running   0             24m
prometheus           prometheus-grafana-69f9ccfd8d-72xb8                      3/3     Running   0             25m
prometheus           prometheus-kube-prometheus-operator-6f4fc4dcbd-2hzqm     1/1     Running   0             25m
prometheus           prometheus-kube-state-metrics-57c8464f66-7h25x           1/1     Running   0             25m
prometheus           prometheus-prometheus-kube-prometheus-prometheus-0       2/2     Running   0             24m
prometheus           prometheus-prometheus-node-exporter-h7gp6                1/1     Running   0             25m

During scaling:

$ kubectl get hpa -n metrics-test-istio
NAME                       REFERENCE                                        TARGETS           MINPODS   MAXPODS   REPLICAS   AGE
metrics-test-istio-00001   Deployment/metrics-test-istio-00001-deployment   105370m/5 (avg)   1         10        1          15m

$ kubectl get po -n metrics-test-istio
NAME                                                   READY   STATUS    RESTARTS   AGE
metrics-test-istio-00001-deployment-7d57bbb8d8-2b7ss   3/3     Running   0          69s
metrics-test-istio-00001-deployment-7d57bbb8d8-2frvl   3/3     Running   0          54s
metrics-test-istio-00001-deployment-7d57bbb8d8-7wn9b   3/3     Running   0          54s
metrics-test-istio-00001-deployment-7d57bbb8d8-86zsg   3/3     Running   0          16m
metrics-test-istio-00001-deployment-7d57bbb8d8-bpbt4   3/3     Running   0          54s
metrics-test-istio-00001-deployment-7d57bbb8d8-fz7qs   3/3     Running   0          39s
metrics-test-istio-00001-deployment-7d57bbb8d8-gx5sb   3/3     Running   0          69s
metrics-test-istio-00001-deployment-7d57bbb8d8-l4ght   3/3     Running   0          54s
metrics-test-istio-00001-deployment-7d57bbb8d8-qdp5j   3/3     Running   0          69s
metrics-test-istio-00001-deployment-7d57bbb8d8-s848s   0/3     Pending   0          39s

/kind documentation
/kind enhancement

[knative-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[knative-prow]

Hi @muscionig. Thanks for your PR.

I'm waiting for a knative-extensions member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[cardil]

/cc @skonto

[skonto]

I will open another issue for documenting Openshift ServiceMesh.

[skonto]

I think it is useful to have the strict mode as well. I have an example here. I will create a PR with some more info so we can finalize content.
Btw did you test encrypted traffic with permissive mode and autoscaling?