Add support for RACK_COMMAND to populate broker.rack

README.md

@@ -75,6 +75,15 @@ HOSTNAME_COMMAND=wget -t3 -T2 -qO-  http://169.254.169.254/latest/meta-data/loca
 ```
 Reference: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-metadata.html
 
+## Broker Rack
+
+You can configure the broker rack affinity in different ways
+
+1. explicitly, using ```KAFKA_BROKER_RACK```
+2. via a command, using ```RACK_COMMAND```, e.g. ```RACK_COMMAND: "curl http://169.254.169.254/latest/meta-data/placement/availability-zone"```
+
+In the above example the AWS metadata service is used to put the instance's availability zone in the ```broker.rack``` property.
+
 ## JMX
 
 For monitoring purposes you may wish to configure JMX. Additional to the standard JMX parameters, problems could arise from the underlying RMI protocol used to connect

start-kafka.sh

@@ -33,6 +33,10 @@ if [[ -z "$KAFKA_ADVERTISED_HOST_NAME" && -n "$HOSTNAME_COMMAND" ]]; then
     export KAFKA_ADVERTISED_HOST_NAME=$(eval $HOSTNAME_COMMAND)
 fi
 
+if [[ -n "$RACK_COMMAND" && -z "$KAFKA_BROKER_RACK" ]]; then
+    export KAFKA_BROKER_RACK=$(eval $RACK_COMMAND)
+fi
+
 #Issue newline to config file in case there is not one already
 echo -e "\n" >> $KAFKA_HOME/config/server.properties