1. Install VirtualBox
2. Install Vagrant
3. clone repository
4. cd mysql-proxy-test
5. vagrant up dbmaster
6. vagrant up dbslave1
7. vagrant up dbslave2
8. vagrant up web
9. vagrant ssh web
10. cd /vagrant/test
11. sh create_db.sh
12. sh multi_test.sh
13. mysql -hdbproxy -uadmin -padmin --port=4041
14. select * from backends;

Run #12 multiple times to see the spread across db servers.

You'll see something like this:

mysql> select * from backends;
+-------------+---------------------+-------+------+------+-------------------+
| backend_ndx | address             | state | type | uuid | connected_clients |
+-------------+---------------------+-------+------+------+-------------------+
|           1 | 192.168.35.102:3306 | up    | rw   | NULL |                 2 |
|           2 | 192.168.35.103:3306 | up    | ro   | NULL |                 5 |
|           3 | 192.168.35.104:3306 | up    | ro   | NULL |                 5 |
+-------------+---------------------+-------+------+------+-------------------+
3 rows in set (0.01 sec)

More infromation about mysql-proxy read/write balancing can be found here: http://www.networkworld.com/article/2224080/opensource-subnet/simple-database-load-balancing-with-mysql-proxy.html