Currently setting the `--allocate-node-cidrs` flag to true with an
empty cloud provider causes the kube-controller-manager to crash during
startup.
Fix the issue by checking for an empty cloud provider before setting
up route management on the cloud provider. This change introduces a
change in behavior. The kube-controller-manager now supports allocating
pod CIDRs without a cloud provider. This means users must manage routes
through some other mechanism.
The controller manager logs a warning if `--allocate-node-cidrs` is set,
but not a cloud provider:
```
I0725 17:10:41.587888 43185 plugins.go:70] No cloud provider specified.
I0725 17:10:41.588036 43185 nodecontroller.go:114] Sending events to api server.
E0725 17:10:41.588122 43185 controllermanager.go:201] Failed to start service controller: ServiceController should not be run without a cloudprovider.
W0725 17:10:41.588136 43185 controllermanager.go:213] allocate-node-cidrs is set, but no cloud provider specified. Will not manage routes.
E0725 17:10:41.589703 43185 nodecontroller.go:187] Error monitoring node status: Get http://127.0.0.1:8080/api/v1/nodes: dial tcp 127.0.0.1
```
Fixes#11866
93a374512e