Support turning on alpha features using feature gates

[yujuhong]

minikube already supports all alpha api resources to encourage people to try them out. It should also support turning on alpha features in the feature gate.
https://github.com/kubernetes/kubernetes/blob/v1.5.0-beta.2/pkg/genericapiserver/options/server_run_options.go#L531
https://github.com/kubernetes/kubernetes/blob/v1.5.0-beta.2/pkg/util/config/feature_gate.go

[yujuhong]

/cc @kubernetes/sig-node @timstclair , we can't turn on CRI in minikube without it supporting the feature gates.

[feiskyer]

+1

[timstclair]

/cc @jlowdermilk

[r2d4]

We can already enable this with the --extra-config flag but I'm open to making it easier to enable though a different way

[yujuhong]

@r2d4 I was not able to enable feature gate using --extra-config at all. I skimmed the code and it seems to me that feature gates were directly set through flags, and not included in ServerRunOptions. Could you provide an example of how this could be done?

[dlorenc]

Yeah, we might need to add some code to make featuregate's work. I'll look through the code now.

[r2d4]

Sorry, it looks like you can't enable them through the config. How can I validate that these are actually enabled? Would something like this work?

diff --git a/pkg/localkube/servers.go b/pkg/localkube/servers.go
index 251c8ff..b812bb7 100644
--- a/pkg/localkube/servers.go
+++ b/pkg/localkube/servers.go
@@ -18,6 +18,7 @@ package localkube
 
 import (
        "fmt"
+       "k8s.io/kubernetes/pkg/util/config"
 )
 
 // Servers allows operations to be performed on many servers at once.
@@ -36,6 +37,7 @@ func (servers Servers) Get(name string) (Server, error) {
 
 // StartAll starts all services, starting from 0th item and ascending.
 func (servers Servers) StartAll() {
+       config.DefaultFeatureGate.Set("AllAlpha=true")
        for _, server := range servers {
                fmt.Printf("Starting %s...\n", server.Name())
                server.Start()

$ minikube logs | grep feature
I1208 23:29:29.585829    3084 feature_gate.go:161] feature gates: map[AllAlpha:true DynamicKubeletConfig:true DynamicVolumeProvisioning:true AllowExtTrafficLocalEndpoints:true]

[j3ffml]

@r2d4 I'm not super familiar with minikube, but if you want to always enable alpha features the above snippet will work. You would need similar line in every kube system binary (kublet, apiserver, controller manager, scheduler etc). featuregates are set via a flag (with same value) on every system component if you are deploying k8s normally.

[yujuhong]

@r2d4 this should work since localkube is a single binary and all components are started in one process.

[r2d4]

Any thoughts on the UI to configure this through minikube?
minikube start --feature-gates?

I don't think it makes much sense to do it as a special case of the extra config, but that wouldn't require an extra flag
minikube start --extra-config=global.feature-gates=

[dlorenc]

Is there any downside to enabling them all, all the time?

[yujuhong]

Is there any downside to enabling them all, all the time?

One downside could be that the alpha features don't work well together. There is one jenkins build that enabling all of them (https://k8s-testgrid.appspot.com/google-gce#gce-alpha-features), but it runs very few tests.

[yujuhong]

minikube start --feature-gates?

This sounds good to me.

[yujuhong]

@r2d4 thanks for adding the feature!