Gloo pod panics with empty static.hosts upstream configured in failoverscheme as primary

Gloo Edge Version

1.10.x

Kubernetes Version

1.23.x

Describe the bug

Having VirtualService point to upstream with empty static.hosts configuration causes the gloo pod to panic on upstream validation when the upstream is primary target of a failoverscheme.

Steps to reproduce the bug

Setup 2 glooe clusters and register them for federation.
enable failover and apply following steps in local(mgmt) cluster

Configure static upstream with empty static.hosts and virtualservice routing to the upstream


apiVersion: gloo.solo.io/v1
kind: Upstream
metadata:
name: custom-service-blue-10000
namespace: gloo-system
spec:
healthChecks:
- healthyThreshold: 1
httpHealthCheck:
  path: /health
interval: 1s
timeout: 1s
unhealthyThreshold: 1
static:
hosts:
---
apiVersion: gateway.solo.io/v1
kind: VirtualService
metadata:
name: vs
namespace: gloo-system
spec:
virtualHost:
routes:
  - matchers:
      - prefix: /
    routeAction:
      single:
        upstream:
          name: custom-service-blue-10000
          namespace: gloo-system

5. Apply failoverscheme pointing to the misconfigured upstream:

kubectl apply -f - <<EOF apiVersion: fed.solo.io/v1 kind: FailoverScheme metadata: finalizers:

fed.solo.io/finalizer name: failover-scheme namespace: gloo-system spec: failoverGroups:
priorityGroup:
- cluster: remote upstreams:
  - name: default-service-green-10000 namespace: gloo-system primary: clusterName: local name: custom-service-blue-10000 namespace: gloo-system
```
6. Gloo pod enters a CrashLoopBack with following log:
```
    {"level":"info","ts":"2022-04-08T09:54:59.199Z","logger":"proxy-validator","caller":"validation/server.go:181","msg":"received proxy validation request"} panic: runtime error: invalid memory address or nil pointer dereference [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x32bd8ea]

goroutine 554 [running]: github.com/solo-io/solo-projects/projects/gloo/pkg/plugins/failover.(failoverPluginImpl).ProcessUpstream(0xc001a43050, 0x4c52cf0, 0xc00300efc0, 0xc0017b8700, 0xc002eb89c0, 0xc002f3dc00, 0x0, 0x0) /workspace/solo-projects/projects/gloo/pkg/plugins/failover/plugin.go:137 +0x74a github.com/solo-io/gloo/projects/gloo/pkg/translator.(translatorInstance).computeCluster(0xc002db6e58, 0x4c52cf0, 0xc00300efc0, 0xc0017b8700, 0xc002eb89c0, 0xc00300ecc0, 0xc00300ec90, 0x0) /go/pkg/mod/github.com/solo-io/gloo@v1.10.10/projects/gloo/pkg/translator/clusters.go:65 +0x22f github.com/solo-io/gloo/projects/gloo/pkg/translator.(translatorInstance).computeClusters(0xc002db6e58, 0x4c52cf0, 0xc00300ee40, 0xc0017b8700, 0xc00300ec90, 0xc00300ecc0, 0xc002de6300, 0x0, 0x0, 0x0, ...) /go/pkg/mod/github.com/solo-io/gloo@v1.10.10/projects/gloo/pkg/translator/clusters.go:47 +0x39f github.com/solo-io/gloo/projects/gloo/pkg/translator.(translatorInstance).translateClusterSubsystemComponents(0xc002db6e58, 0x4c52cf0, 0xc00300e9c0, 0xc0017b8700, 0xc002de6300, 0xc00300ec90, 0x0, 0x0, 0x0, 0x0, ...) /go/pkg/mod/github.com/solo-io/gloo@v1.10.10/projects/gloo/pkg/translator/translator.go:163 +0x436 github.com/solo-io/gloo/projects/gloo/pkg/translator.(translatorInstance).Translate(0xc002db6e58, 0x4c52cf0, 0xc00300e9c0, 0xc0017b8700, 0xc002de6300, 0x0, 0x0, 0x0, 0x0, 0x0, ...) /go/pkg/mod/github.com/solo-io/gloo@v1.10.10/projects/gloo/pkg/translator/translator.go:119 +0x4f6 github.com/solo-io/gloo/projects/gloo/pkg/translator.(translatorFactory).Translate(0xc0017af4d0, 0x4c52cf0, 0xc00300e630, 0xc0017b8700, 0xc002de6300, 0x0, 0x0, 0x0, 0x0, 0x0, ...) /go/pkg/mod/github.com/solo-io/gloo@v1.10.10/projects/gloo/pkg/translator/translator.go:79 +0x27f github.com/solo-io/gloo/projects/gloo/pkg/validation.(validator).Validate(0xc001bc9200, 0x4c52cf0, 0xc00300e630, 0xc002ea6a80, 0x0, 0x0, 0x0) /go/pkg/mod/github.com/solo-io/gloo@v1.10.10/projects/gloo/pkg/validation/server.go:192 +0x472 github.com/solo-io/gloo/projects/gloo/pkg/validation.(validationServer).Validate(0xc000c0dfb0, 0x4c52cf0, 0xc002ee42d0, 0xc002ea6a80, 0x0, 0x0, 0x0) /go/pkg/mod/github.com/solo-io/gloo@v1.10.10/projects/gloo/pkg/validation/server.go:350 +0xe2 github.com/solo-io/gloo/projects/gloo/pkg/api/grpc/validation._GlooValidationService_Validate_Handler(0x4348640, 0xc000c0dfb0, 0x4c52cf0, 0xc002ee42d0, 0xc002e14f00, 0x0, 0x0, 0x0, 0x0, 0x0) /go/pkg/mod/github.com/solo-io/gloo@v1.10.10/projects/gloo/pkg/api/grpc/validation/gloo_validation.pb.go:2621 +0x3d9 google.golang.org/grpc.(Server).processUnaryRPC(0xc000a3f880, 0x4c6c0f8, 0xc002363980, 0xc002e85d40, 0xc001c1fa40, 0x66787a0, 0x0, 0x0, 0x0) /go/pkg/mod/google.golang.org/grpc@v1.42.0/server.go:1282 +0x105d google.golang.org/grpc.(Server).handleStream(0xc000a3f880, 0x4c6c0f8, 0xc002363980, 0xc002e85d40, 0x0) /go/pkg/mod/google.golang.org/grpc@v1.42.0/server.go:1616 +0x9f9 google.golang.org/grpc.(Server).serveStreams.func1.2(0xc002e7abb0, 0xc000a3f880, 0x4c6c0f8, 0xc002363980, 0xc002e85d40) /go/pkg/mod/google.golang.org/grpc@v1.42.0/server.go:921 +0xf4 created by google.golang.org/grpc.(Server).serveStreams.func1 /go/pkg/mod/google.golang.org/grpc@v1.42.0/server.go:919 +0x2c5



### Expected Behavior

I'd expect an error message logged, but pod would continue to run

### Additional Context

_No response_

solo-io / gloo