Merge pull request #3116 from DataDog/haissam/improve-get_hostname-fo…

…r-docker

[docker/hostname] improve get_hostname for containers

utils/dockerutil.py

@@ -177,25 +177,29 @@ def get_gateway(cls, proc_prefix=""):
 
         return None
 
-    def get_hostname(self, use_default_gw=True):
+    def get_hostname(self, use_default_gw=True, should_resolve=False):
         '''
         Return the `Name` param from `docker info` to use as the hostname
         Falls back to the default route.
         '''
+        # return or raise
+        is_resolvable = lambda host: socket.gethostbyname(host)
 
         if self.hostname is not None:
             # Use cache
-            return self.hostname
+            try:
+                if not should_resolve or is_resolvable(self.hostname):
+                    return self.hostname
+            except Exception:
+                log.debug("Couldn't resolve cached hostname %s, triggering new hostname detection." % self.hostname)
 
         if self._default_gateway is not None and use_default_gw:
             return self._default_gateway
 
         try:
-            docker_host_name = self.client.info().get("Name")
-            socket.gethostbyname(docker_host_name) # make sure we can resolve it
-            self.hostname = docker_host_name
-            return docker_host_name
-
+            self.hostname = self.client.info().get("Name")
+            if not should_resolve or is_resolvable(self.hostname):
+                return self.hostname
         except Exception as e:
             log.debug("Unable to retrieve hostname using docker API, %s", str(e))
             if not use_default_gw:

utils/kubernetes/kubeutil.py

@@ -136,7 +136,7 @@ def _locate_kubelet(self, instance):
         if not host:
             # if no hostname was provided, use the docker hostname if cert
             # validation is not required, the kubernetes hostname otherwise.
-            docker_hostname = self.docker_util.get_hostname()
+            docker_hostname = self.docker_util.get_hostname(should_resolve=True)
             if self.tls_settings.get('kubelet_verify'):
                 try:
                     k8s_hostname = self.get_node_hostname(docker_hostname)