Add health check using TCP

[shamsher31]

Based on istio/istio.io#8246 (comment)

Follow up for istio/istio.io#8246

$ kubectl get pods
NAME                             READY   STATUS    RESTARTS   AGE
liveness-http-86c7cc8f45-s4h7m   1/1     Running   0          1m
liveness-tcp-59f6d56f7-69f7k     1/1     Running   0          2m

Using the HTTP probe

$ kubectl describe pod liveness-http-86c7cc8f45-s4h7m
...
Liveness:       http-get http://:8001/foo delay=5s timeout=1s period=5s #success=1 #failure=3

Using TCP probe

$ kubectl describe pod liveness-tcp-59f6d56f7-69f7k
...
Liveness:       tcp-socket :8001 delay=5s timeout=1s period=5s #success=1 #failure=3

[gofman8]

TCP health checks does not work at all. Check #15178
the documentation and examples are wrong

[howardjohn]

I am not sure this is right. AFAIK TCP socket health check is broken by design in Istio, since its not possible to proxy a "can I connect" check.

[howardjohn]

you can set this to literally any port and it will pass if the sidecar is injected

[shamsher31]

you can set this to literally any port and it will pass if the sidecar is injected.

Closing this as it's not the correct solution.