HTTP/3 is the successor to HTTP/2, and is the latest version of the Hypertext Transfer Protocol (HTTP). It builds upon the performance and efficiency improvements added in HTTP/2, yet runs on the QUIC protocol instead of TCP. This is why the protocol is also referred to as "HTTP over QUIC."
The Internet Engineering Task Force (IETF) publicly unveiled HTTP/3, which was quickly standardized under RFC 9114 in 2022. However, many foundational internet and networking companies began experimenting with — and developing support for — the protocol in the years prior. HTTP/3 introduced notable performance and security improvements over HTTP/2. For example, HTTPS is now enforced as a requirement and head-of-line blocking is further reduced.
How does HTTP/3 work?
HTTP/3 runs on the Quick UDP Internet Connections (QUIC) protocol. It was developed to be faster and more efficient than TCP — establishing connections faster with reduced sensitivity to packet loss. A packet dropped over TCP triggers retransmission of the entire payload and can add congestion over the network.
Meanwhile, QUIC boasts better resilience to packet loss by deferring to the top-level protocol for retransmission, packet reordering, or inaction. While a dropped packet can cause delays over TCP, HTTP/3 over QUIC may continue to transmit its data streams without performing validation. This unlocks better performance in applications that rely primarily on speed over data integrity.
HTTP/3 also distinguishes the transport layer (Layer 4) connection from the network layer (Layer 3) of the OSI model. As a result, HTTP/3 applications perform a bit better when switching between networks. This happens frequently for mobile users who are typically on the move.
HTTP/3 is also inherently more secure since requests are encrypted by default. The protocol also supports zero round-trip time (0-RTT) for faster connections to known servers. And when an HTTP/3 application connects to a new server for the first time, consolidating the TLS and transport handshakes slashes latency. In many cases, a given HTTP/3 service will perform better than an HTTP/2 equivalent due to this efficiency — and by granting users even greater control over their data streams.
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Does HAProxy support HTTP/3?
Yes! Our HAProxy One application delivery and security platform fully supports HTTP/3. HAProxy Enterprise load balancer routes traffic from any HTTP/3-over-QUIC application using a selection of load-balancing algorithms and supports core performance features such as multiplexing, connection pooling, and HTTP compression.
Explore our load balancing solutions to learn more about protocol support in HAProxy One.