A UDP Load Balancer is a network device or software that distributes incoming User Datagram Protocol (UDP) traffic across multiple backend servers to ensure efficient utilization of resources, high availability, and improved performance of applications. Unlike TCP, UDP is a connectionless and stateless protocol, meaning it does not establish a connection before sending data and does not guarantee delivery, order, or error checking of packets.
Key Features and Functionality
Stateless Protocol Handling:
UDP does not maintain a connection state, making each packet independent. This characteristic requires the load balancer to manage session states to ensure that return traffic is correctly routed back to the client[2][3].
Load Distribution:
The load balancer assigns incoming UDP packets to healthy backend servers based on various algorithms, such as round-robin, least connections, or hash-based methods. This helps in evenly distributing the load and preventing any single server from becoming a bottleneck[4][5].
Health Checks:
To ensure that traffic is only sent to healthy servers, UDP load balancers often use health checks on backend servers. These checks can be performed using TCP, HTTP, or HTTPS protocols since UDP itself does not support built-in health checks[2].
Session Persistence:
Some UDP load balancers maintain session persistence (also known as stickiness) by ensuring that packets from the same client are consistently routed to the same backend server. This is typically achieved using a hash of the source IP and port, destination IP and port, and protocol (5-tuple hash)[8].
Direct Server Return (DSR):
In some configurations, such as with Google Cloud's external passthrough Network Load Balancer, the backend servers send responses directly to the clients, bypassing the load balancer. This method, known as Direct Server Return, reduces latency and load on the load balancer[3].
