fix(kubernetes): switch k8s readiness check from exec to httpGet for ingress support

[paulczar]

services that have a healthcheck defined were getting an exec check
for the kubernetes readiness check and were running a wget command
against localhost to verify health. Kubernetes has the httpGet option
for readiness check that does this in a more k8s native way and doesn't
rely on running a command inside the pod.

This is especially important for people that want to put spinnaker
behind an ingress controller or istio as by default many ingress controllers
look for a http or tcp socket readiness check to be used by the cloud
loadbalancer to ensure the service is up.

From Ingress
documentation:

It’s also worth noting that even though health checks are not exposed directly through the ingress, there exist parallel concepts in Kubernetes such as readiness probes which allow you to achieve the same end result. Please review the controller specific docs to see how they handle health checks ( nginx, GCE).

The Google Ingress controller requires a http/tcp based readiness check
and the nginx Ingress controller can utilize them as well.

fixes spinnaker/spinnaker#3864

Signed-off-by: Paul Czarkowski username.taken@gmail.com

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[paulczar]

Oh also an unavailable version of kubectl was being referenced in the dockerfiles so I had to update that to get a working kubectl in there to verify functionality.

[lwander]

Can you verify this works with the latest istio release? We started using exec as a workaround to their strange tls setup.

[paulczar]

@lwander thanks for the heads up on istio. I've modified this to have a config setting to determine if the healthcheck should be an exec or not, with a default to exec. This way the current functionality with istio works, but is easily flagged to use httpGet instead. This should keep both use cases happy.

[lwander]

Awesome. I'll merge now & could you update the docs here to point out the new flag? https://www.spinnaker.io/reference/halyard/custom/#tweakable-service-settings