Load balance UDP with LVS and NAT

In this section, we describe how to load balance UDP services with the embedded Linux Virtual Server (LVS) to perform the load balancing at layer 4. In this scenario, we set LVS to use its NAT mode to change the destination IP address in packets. We also use the NAT tab to change the source IP address in packets so that responses from servers return through HAProxy ALOHA (that is, not Direct Server Return).

Enable UDP load balancing Jump to heading #

To enable HAProxy ALOHA to load balance UDP at layer 4:

1. Configure LVS on the LB Layer4 tab so that it translates the destination IP from the public VIP on which HAProxy ALOHA listens to a backend server’s private IP. You do this in the director configuration section by setting mode nat and setting one or more server directives.

   In this example, the VIP is 10.0.0.3 and the backend server’s IP is 10.0.0.20. The application listens at port 8000.

   haproxy
   director web 10.0.0.3:8000 UDP
     balance leastconn
     mode nat
     server web1 10.0.0.20:8000 weight 10 check

   haproxy
   director web 10.0.0.3:8000 UDP
     balance leastconn
     mode nat
     server web1 10.0.0.20:8000 weight 10 check

2. Click OK and Apply.

3. Go to the NAT tab and click Insert to add a NAT rule. In the New Rule area, fill in the fields as described below to create a NAT rule that changes the client’s source IP to the HAProxy ALOHA appliance’s IP.

   Field	Description
   IN	Inbound network interface. This indicates the interface of your VIP, where you receive traffic from clients.
   OUT	Outbound network interface. If your appliance has only one network interface, set this to the same as the inbound interface. If your appliance has two interfaces and one of those interfaces is in a network containing the backend servers, use that interface for OUT.
   Protocol	UDP.
   Before - Source	Leave blank or set to any, which means match any source IP address.
   Before - Source port	Leave blank or set to any, which means match any source port. Source ports are random.
   Before - Destination	The VIP address that clients connect to, to match traffic destined for that address.
   Before - Destination port	The UDP port of your application. You can set a single port like 8000, or a port range like 50000-51000.
   After - Source	The VIP address to set as the source address on incoming packets. We recommend using a VIP instead of a physical IP address so that it’s highly available between HAProxy ALOHA appliances. When you have two network interfaces, you can create a new VIP for the private network containing your real servers, to better differentiate client-facing and server-facing traffic by having two, distinct VIPs. In contrast, a physical IP address can’t be shared between the members of a cluster.
   After - Source port	Leave blank or set to same, since we won’t change the source port.
   After - Destination	Leave blank or set to same, since we won’t change the destination IP address via the NAT tab. Destination NAT is handled by LVS.
   After - Destination port	Leave blank or set to same, since we won’t change the destination port.

   Info

   In configurations having two network interfaces, if you have failover configured on one VIP, configure a VIP with failover on the other interface as well.

4. Check your NAT configuration.

   • One network interface (IN and OUT fields are the same, there is one VIP).

   

   • Two network interfaces (IN and OUT fields differ, there are two VIPs).

   

5. Click Add and Apply.

6. To ensure that packets from the same client flow to the same backend server during a session, enable LVS connection tracking. Click the Services tab, locate the lvs service, and click Setup.

7. If the configuration contains the line no autostart, delete the line to ensure that the LVS service starts automatically on boot.

8. Enable connection tracking through the conntrack keyword.

   text
   service lvs
     ############ Linux Virtual Server, layer 3/4 load balancing
     conntrack

   text
   service lvs
     ############ Linux Virtual Server, layer 3/4 load balancing
     conntrack

9. Click OK and then Close.

10. Locate the lvs service and click Restart.

11. To make the changes persist after a reboot, go to the Setup tab and click Save within the Configuration section.