Boost Spring Boot Performance: Switch from Tomcat to Undertow and Optimize Settings

Optimization Background

When your application needs to support instantaneous high concurrency, Tomcat is no longer the optimal choice; you can switch to Undertow and optimize it.

Undertow is a lightweight, high‑performance Java web server developed by JBoss and open‑sourced. It is based on a non‑blocking I/O model, offering low resource consumption and high concurrency handling.

Switch Spring Boot 3 from Tomcat to Undertow

Add the following dependencies to pom.xml to exclude Tomcat and include Undertow:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

Thread‑Pool Optimization

Add the following configuration to application.yml or application.properties:

server:
  undertow:
    # Thread pool configuration
    threads:
      # I/O threads (recommend 1‑2× CPU cores)
      io: 16
      # Worker threads (recommend 8‑16× CPU cores)
      worker: 256
    # Buffer configuration
    buffer-size: 1024
    direct-buffers: true

Request Timeout Limits

server:
  undertow:
    # Request timeout (ms)
    no-request-timeout: 30000
    # Idle connection timeout (ms)
    idle-timeout: 60000

Limit Request Body Size to 2 KB

server:
  undertow:
    max-http-post-size: 2048

Enable Response Compression

Spring Boot’s server compression reduces response size, improves transfer efficiency, and speeds up page loading.

Benefits

Reduce data transfer: compressed payloads lower network overhead.

Improve load speed: especially for front‑end pages and API responses.

Lower server load: less transmission time increases throughput.

Better user experience: faster page loads.

Recommended Configuration

server:
  compression:
    enabled: true   # enable compression
    min-response-size: 1024
    mime-types: application/json, text/html, text/xml, text/plain, text/css, application/javascript
    excluded-user-agents: IE6, IE7

Enable HTTP/2 (requires SSL)

server:
  http2:
    enabled: true

Undertow Access Log Configuration

server:
  undertow:
    accesslog:
      enabled: true
      dir: ./logs
      prefix: access_log.
      suffix: .log
      pattern: '%t %a "%r" %s (%D ms)'
      rotate: true

Monitoring and Tuning Recommendations

Monitor thread‑pool status: use JMX or Actuator.

Stress testing: run JMeter or wrk load tests.

JVM tuning: adjust heap and GC parameters based on load.

Connection‑pool tuning: ensure DB pool size matches server thread count.