Merge pull request #56196 from juju-solutions/bug/lowercase-hostname-label

Automatic merge from submit-queue (batch tested with PRs 55925, 55999, 55944, 55992, 56196). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Lowercase hostnames when used as node names in k8s

**What this PR does / why we need it**: Juju deployments of Kubernetes should lowercase the hostnames when referencing nodes.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*: https://github.com/juju-solutions/bundle-canonical-kubernetes/issues/442


**Special notes for your reviewer**:

**Release note**:

```NONE 
```

cluster/juju/layers/kubernetes-worker/reactive/kubernetes_worker.py

@@ -157,7 +157,7 @@ def shutdown():
     '''
     try:
         if os.path.isfile(kubeconfig_path):
-            kubectl('delete', 'node', gethostname())
+            kubectl('delete', 'node', gethostname().lower())
     except CalledProcessError:
         hookenv.log('Failed to unregister node.')
     service_stop('snap.kubelet.daemon')
@@ -844,14 +844,14 @@ def request_kubelet_and_proxy_credentials(kube_control):
     # The kube-cotrol interface is created to support RBAC.
     # At this point we might as well do the right thing and return the hostname
     # even if it will only be used when we enable RBAC
-    nodeuser = 'system:node:{}'.format(gethostname())
+    nodeuser = 'system:node:{}'.format(gethostname().lower())
     kube_control.set_auth_request(nodeuser)
 
 
 @when('kube-control.connected')
 def catch_change_in_creds(kube_control):
     """Request a service restart in case credential updates were detected."""
-    nodeuser = 'system:node:{}'.format(gethostname())
+    nodeuser = 'system:node:{}'.format(gethostname().lower())
     creds = kube_control.get_auth_credentials(nodeuser)
     if creds \
             and data_changed('kube-control.creds', creds) \
@@ -906,7 +906,8 @@ class ApplyNodeLabelFailed(Exception):
 def _apply_node_label(label, delete=False, overwrite=False):
     ''' Invoke kubectl to apply node label changes '''
 
-    hostname = gethostname()
+    # k8s lowercases hostnames and uses them as node names
+    hostname = gethostname().lower()
     # TODO: Make this part of the kubectl calls instead of a special string
     cmd_base = 'kubectl --kubeconfig={0} label node {1} {2}'