instances.diff

diff --git a/src/main/java/io/vertx/core/Vertx.java b/src/main/java/io/vertx/core/Vertx.java
index af83f3a..521968b 100644
--- a/src/main/java/io/vertx/core/Vertx.java
+++ b/src/main/java/io/vertx/core/Vertx.java
@@ -441,6 +441,13 @@ public interface Vertx extends Measured {
    */
   boolean isClustered();
 
+   /**
+    * The number of verticle instances associated to a deployment id
+    *
+    * @return the number of verticles associated to a deployment id or -1 if there are none
+    */
+   int getInstanceCount(String deploymentId);
+
   /**
    * Safely execute some blocking code.
    * <p>
diff --git a/src/main/java/io/vertx/core/impl/VertxImpl.java b/src/main/java/io/vertx/core/impl/VertxImpl.java
index 67f089b..1f7f749 100644
--- a/src/main/java/io/vertx/core/impl/VertxImpl.java
+++ b/src/main/java/io/vertx/core/impl/VertxImpl.java
@@ -137,6 +137,7 @@ public class VertxImpl implements VertxInternal, MetricsProvider {
     this.deploymentManager = new DeploymentManager(this);
     this.metrics = initialiseMetrics(options);
     this.haEnabled = options.isClustered() && options.isHAEnabled();
+
     if (options.isClustered()) {
       this.clusterManager = getClusterManager(options);
       this.clusterManager.setVertx(this);
@@ -202,6 +203,16 @@ public class VertxImpl implements VertxInternal, MetricsProvider {
     }
   }
 
+  @Override
+  public int getInstanceCount(String deploymentId) {
+      Deployment deployment = deploymentManager.getDeployment(deploymentId);
+      if (deployment != null) {
+          return deployment.deploymentOptions().getInstances();
+      }
+
+      return -1;
+  }
+
   /**
    * @return The FileSystem implementation for the OS
    */