Corrected example of providing Turbine cluster name via instance metadata map.

docs/src/main/asciidoc/spring-cloud-netflix.adoc

@@ -517,7 +517,7 @@ turbine:
   aggregator:
     clusterConfig: SYSTEM,USER
   appConfig: customers,stores,ui,admin
-  clusterNameExpression: metadata.cluster
+  clusterNameExpression: metadata['cluster']
 ----
 
 In this case, the cluster name from 4 services is pulled from their metadata map, and is expected to have values that include "SYSTEM" and "USER".

spring-cloud-netflix-turbine/src/test/java/org/springframework/cloud/netflix/turbine/EurekaInstanceDiscoveryTest.java

@@ -50,4 +50,16 @@ public class EurekaInstanceDiscoveryTest {
 		assertEquals("clusterName is wrong", asgName, clusterName);
 	}
 
+	@Test
+	public void testGetClusterNameInstanceMetadataMapExpression() {
+		TurbineProperties turbineProperties = new TurbineProperties();
+		turbineProperties.setClusterNameExpression("metadata['cluster']");
+		EurekaInstanceDiscovery discovery = new EurekaInstanceDiscovery(turbineProperties);
+		String metadataProperty = "myCluster";
+		InstanceInfo instanceInfo = InstanceInfo.Builder.newBuilder()
+				.setAppName("testApp").add("cluster", metadataProperty).build();
+		String clusterName = discovery.getClusterName(instanceInfo);
+		assertEquals("clusterName is wrong", metadataProperty, clusterName);
+	}
+
 }