Instance Caching

This is the work to complete the resource-metadata-caching blueprint.

* Implement an in-memory cache in the compute agent.
* Change compute-agent to populate an in-memory cache.
* Change compute-agent to use the changes-since parameter in the Nova API call .
* Change compute-agent to record the polling timestamp in the cache.
* Change compute-agent to cache the flavor and image metadata as well.

Closes-Bug: #1524166

Change-Id: I97594e082db6d8e34d9201a7ec5710978e557d6d
Signed-off-by: Jason Myers <jason@jasonamyers.com>
(cherry picked from commit 7050d3be10788d695d83d7162bc5e078622a982d)

2 files changed, 21 insertions, 5 deletions

diff --git a/ceilometer/compute/discovery.py b/ceilometer/compute/discovery.py
index ac6afafd..e85d067b 100644
--- a/ceilometer/compute/discovery.py
+++ b/ceilometer/compute/discovery.py
@@ -14,6 +14,7 @@
 # under the License.
 
 from oslo_config import cfg
+from oslo_utils import timeutils
 
 from ceilometer.agent import plugin_base
 from ceilometer import nova_client
@@ -31,12 +32,21 @@ class InstanceDiscovery(plugin_base.DiscoveryBase):
     def __init__(self):
         super(InstanceDiscovery, self).__init__()
         self.nova_cli = nova_client.Client()
+        self.last_run = None
+        self.instances = {}
 
     def discover(self, manager, param=None):
         """Discover resources to monitor."""
-        instances = self.nova_cli.instance_get_all_by_host(cfg.CONF.host)
-        return [i for i in instances
-                if getattr(i, 'OS-EXT-STS:vm_state', None) != 'error']
+        instances = self.nova_cli.instance_get_all_by_host(
+            cfg.CONF.host, self.last_run)
+        for instance in instances:
+            if getattr(instance, 'OS-EXT-STS:vm_state', None) in ['deleted',
+                                                                  'error']:
+                self.instances.pop(instance.id, None)
+            else:
+                self.instances[instance.id] = instance
+        self.last_run = timeutils.utcnow(True).isoformat()
+        return self.instances.values()
 
     @property
     def group_id(self):
diff --git a/ceilometer/nova_client.py b/ceilometer/nova_client.py
index 8b09219a..cce5139d 100644
--- a/ceilometer/nova_client.py
+++ b/ceilometer/nova_client.py
@@ -137,9 +137,15 @@ class Client(object):
             setattr(instance, attr, ameta)
 
     @logged
-    def instance_get_all_by_host(self, hostname):
-        """Returns list of instances on particular host."""
+    def instance_get_all_by_host(self, hostname, since=None):
+        """Returns list of instances on particular host.
+
+        If since is supplied, it will return the instances changed since that
+        datetime. since should be in ISO Format '%Y-%m-%dT%H:%M:%SZ'
+        """
         search_opts = {'host': hostname, 'all_tenants': True}
+        if since:
+            search_opts['changes-since'] = since
         return self._with_flavor_and_image(self.nova_client.servers.list(
             detailed=True,
             search_opts=search_opts))