Performance Tuning Guide for Undertow Web Server

Undertow is an open‑source high‑performance Java web server from Red Hat, offering both BIO and NIO mechanisms.

Why not tune Tomcat? While Tomcat can be tuned, Undertow generally outperforms it in speed and memory, making a direct switch preferable.

How to optimize Undertow

Thread pool configuration

Adjust the I/O and worker thread counts in application.yml :

server.undertow.io-threads=8

server.undertow.worker-threads=128

Buffer and memory settings

Typical values:

server.undertow.buffer-size=1024

server.undertow.direct-buffers=true

server.undertow.buffers-per-region=...

Connection and request timeouts

server.undertow.max-http-post-size=0

server.undertow.no-request-timeout=1800s

Disable unnecessary features

server.undertow.session-cookie-config=none

server.undertow.accesslog.enabled=false

Programmatic configuration can be done by implementing WebServerFactoryCustomizer<UndertowServletWebServerFactory> .

Enable HTTP/2 via server.undertow.enabled-http2=true .

Example application.yml snippet:

# IO threads
server.undertow.io-threads=16

# Worker threads
server.undertow.worker-threads=128

# Buffer size
server.undertow.buffer-size=512

# Direct buffers
server.undertow.direct-buffers=true

# HTTP/2
server.undertow.enabled-http2=true