diff --git a/core/api/src/main/java/org/onlab/onos/cluster/ClusterEvent.java b/core/api/src/main/java/org/onlab/onos/cluster/ClusterEvent.java
new file mode 100644
index 0000000..6737f68
--- /dev/null
+++ b/core/api/src/main/java/org/onlab/onos/cluster/ClusterEvent.java
@@ -0,0 +1,58 @@
+package org.onlab.onos.cluster;
+
+import org.onlab.onos.event.AbstractEvent;
+
+/**
+ * Describes cluster-related event.
+ */
+public class ClusterEvent extends AbstractEvent<ClusterEvent.Type, ControllerInstance> {
+
+    /**
+     * Type of device events.
+     */
+    public enum Type {
+        /**
+         * Signifies that a new cluster instance has been administratively added.
+         */
+        INSTANCE_ADDED,
+
+        /**
+         * Signifies that a cluster instance has been administratively removed.
+         */
+        INSTANCE_REMOVED,
+
+        /**
+         * Signifies that a cluster instance became active.
+         */
+        INSTANCE_ACTIVE,
+
+        /**
+         * Signifies that a cluster instance became inactive.
+         */
+        INSTANCE_INACTIVE
+    }
+    // TODO: do we need to fix the verv/adjective mix? discuss
+
+    /**
+     * Creates an event of a given type and for the specified instance and the
+     * current time.
+     *
+     * @param type     cluster event type
+     * @param instance cluster device subject
+     */
+    public ClusterEvent(Type type, ControllerInstance instance) {
+        super(type, instance);
+    }
+
+    /**
+     * Creates an event of a given type and for the specified device and time.
+     *
+     * @param type     device event type
+     * @param instance event device subject
+     * @param time     occurrence time
+     */
+    public ClusterEvent(Type type, ControllerInstance instance, long time) {
+        super(type, instance, time);
+    }
+
+}
diff --git a/core/api/src/main/java/org/onlab/onos/cluster/ClusterService.java b/core/api/src/main/java/org/onlab/onos/cluster/ClusterService.java
new file mode 100644
index 0000000..afbf0d5
--- /dev/null
+++ b/core/api/src/main/java/org/onlab/onos/cluster/ClusterService.java
@@ -0,0 +1,29 @@
+package org.onlab.onos.cluster;
+
+import java.util.Set;
+
+/**
+ * Service for obtaining information about the individual instances within
+ * the controller cluster.
+ */
+public interface ClusterService {
+
+    /**
+     * Returns the set of current cluster members.
+     *
+     * @return set of cluster members
+     */
+    Set<ControllerInstance> getInstances();
+
+    /**
+     * Returns the availability state of the specified controller instance.
+     *
+     * @return availability state
+     */
+    ControllerInstance.State getState(ControllerInstance instance);
+    // TODO: determine if this would be better attached to ControllerInstance directly
+
+
+    // addListener, removeListener
+
+}
diff --git a/core/api/src/main/java/org/onlab/onos/cluster/ControllerInstance.java b/core/api/src/main/java/org/onlab/onos/cluster/ControllerInstance.java
new file mode 100644
index 0000000..66d753e
--- /dev/null
+++ b/core/api/src/main/java/org/onlab/onos/cluster/ControllerInstance.java
@@ -0,0 +1,38 @@
+package org.onlab.onos.cluster;
+
+import org.onlab.packet.IpAddress;
+
+/**
+ * Represents a controller instance as a member in a cluster.
+ */
+public interface ControllerInstance {
+
+    /** Represents the operational state of the instance. */
+    public enum State {
+        /**
+         * Signifies that the instance is active and operating normally.
+         */
+        ACTIVE,
+
+        /**
+         * Signifies that the instance is inactive, which means either down or
+         * up, but not operational.
+         */
+        INACTIVE
+    }
+
+    /**
+     * Returns the instance identifier.
+     *
+     * @return instance identifier
+     */
+    InstanceId id();
+
+    /**
+     * Returns the IP address of the controller instance.
+     *
+     * @return IP address
+     */
+    IpAddress ip();
+
+}
diff --git a/core/api/src/main/java/org/onlab/onos/cluster/InstanceId.java b/core/api/src/main/java/org/onlab/onos/cluster/InstanceId.java
new file mode 100644
index 0000000..7292a85
--- /dev/null
+++ b/core/api/src/main/java/org/onlab/onos/cluster/InstanceId.java
@@ -0,0 +1,7 @@
+package org.onlab.onos.cluster;
+
+/**
+ * Controller cluster identity.
+ */
+public interface InstanceId {
+}
diff --git a/core/api/src/main/java/org/onlab/onos/cluster/package-info.java b/core/api/src/main/java/org/onlab/onos/cluster/package-info.java
new file mode 100644
index 0000000..3cb37c3
--- /dev/null
+++ b/core/api/src/main/java/org/onlab/onos/cluster/package-info.java
@@ -0,0 +1,4 @@
+/**
+ * Set of abstractions for dealing with controller cluster related topics.
+ */
+package org.onlab.onos.cluster;
\ No newline at end of file
diff --git a/core/api/src/main/java/org/onlab/onos/net/flow/FlowRuleEvent.java b/core/api/src/main/java/org/onlab/onos/net/flow/FlowRuleEvent.java
index 566c2b4..ce8e700 100644
--- a/core/api/src/main/java/org/onlab/onos/net/flow/FlowRuleEvent.java
+++ b/core/api/src/main/java/org/onlab/onos/net/flow/FlowRuleEvent.java
@@ -19,7 +19,7 @@
         /**
          * Signifies that a flow rule has been removed.
          */
-        RULE_REMOVED,
+        RULE_REMOVED
     }
 
     /**
diff --git a/core/api/src/main/java/org/onlab/onos/net/flow/FlowRuleService.java b/core/api/src/main/java/org/onlab/onos/net/flow/FlowRuleService.java
index 71434c7..ba75ae9 100644
--- a/core/api/src/main/java/org/onlab/onos/net/flow/FlowRuleService.java
+++ b/core/api/src/main/java/org/onlab/onos/net/flow/FlowRuleService.java
@@ -23,6 +23,8 @@
      */
     Iterable<FlowEntry> getFlowEntries(DeviceId deviceId);
 
+    // TODO: add createFlowRule factory method and execute operations method
+
     /**
      * Applies the specified flow rules onto their respective devices. These
      * flow rules will be retained by the system and re-applied anytime the
@@ -46,9 +48,6 @@
     void removeFlowRules(FlowRule... flowRules);
 
 
-    // void addInitialFlowContributor(InitialFlowContributor contributor);
-    // void removeInitialFlowContributor(InitialFlowContributor contributor);
-
     /**
      * Adds the specified flow rule listener.
      *