[docker_daemon] adding whitelist for docker health service checks.

[docker_daemon] whitelist health service checks yaml update.

[docker_daemon] whitelist is a set for O(1) average complexity.

checks.d/docker_daemon.py

@@ -274,7 +274,8 @@ def check(self, instance):
 
         # Report docker healthcheck SC's where available
         if health_service_checks:
-            self._send_container_healthcheck_sc(containers_by_id)
+            health_scs_whitelist = set(instance.get('health_service_check_whitelist', []))
+            self._send_container_healthcheck_sc(containers_by_id, health_scs_whitelist)
 
     def _count_and_weigh_images(self):
         try:
@@ -521,8 +522,12 @@ def _report_container_size(self, containers_by_id):
                     self, 'docker.container.size_rootfs', container['SizeRootFs'],
                     tags=tags)
 
-    def _send_container_healthcheck_sc(self, containers_by_id):
+    def _send_container_healthcheck_sc(self, containers_by_id, whitelist):
+        """Send health service checks for containers. Whitelist should preferably be a set."""
         for container in containers_by_id.itervalues():
+            if container.get('Image') not in whitelist:
+                continue
+
             health = container.get('health', {})
             tags = self._get_tags(container, CONTAINER)
             status = AgentCheck.UNKNOWN

conf.d/docker_daemon.yaml.example

@@ -57,7 +57,11 @@ instances:
     #       Container Healthchecks are available starting with docker 1.12, enabling with older
     #       versions will result in an UNKNOWN state for the service check.
     #
+    # You should whitelist the container images you wish to submit health service checks for.
+    # Example: ["tomcat", "nginx", "etcd"]
+    #
     # health_service_checks: false
+    # health_service_check_whitelist: []
 
     # Collect images stats
     # Number of available active images and intermediate images as gauges.