Katran is a C++ library and Berkeley Packet Filter program that builds high-performance layer 4 load balancing forwarding planes.
Katran solves the problem of scaling layer 4 load balancing by leveraging the kernel's XDP infrastructure for in-kernel packet processing. Rather than relying on userspace networking or traditional kernel mechanisms, it uses eBPF programs to achieve fast packet forwarding. The tool operates in direct service response mode, where traffic is forwarded directly from backend servers to clients without returning through the load balancer, eliminating a potential bottleneck. Performance scales linearly with the number of NIC receive queues, and the encapsulation approach is designed to work well with receive-side scaling.
Katran suits infrastructure teams building high-throughput load balancing systems who can meet its environmental requirements and have access to recent Linux kernels. It is particularly valuable when compared to DNS-based traffic redirection, which requires waiting for TTL expiration to handle failures, or anycast-based solutions, which are more vulnerable to network reshuffles and less flexible for managing pool membership changes. Examples are provided using both Thrift and gRPC service endpoints to demonstrate library usage.
Development activity shows active maintenance with CI workflows in place. The project maintains documentation across multiple guides covering overview, usage, development setup, and examples. Build infrastructure is automated through a provided script that handles dependency installation, though the team acknowledges ongoing work to support distributions beyond Ubuntu and welcomes community contributions for broader compatibility.
