spring-boot-virtual-threads

Spring Boot Virtual Threads Contract

These rules apply to servlet/MVC applications. A deployable servlet app must meet this contract. YAML layout and profiles stay in the configuration contract. Outbound RestClient setup stays in the HTTP-client contract.

Enablement

• Enable virtual threads in shared application.yml (not only in one profile):

  spring:
    threads:
      virtual:
        enabled: true
  

• Keep the same value for development and production. Do not disable virtual threads in production as a default.

Runtime model

• Keep the blocking servlet stack: MVC, JDBC, and RestClient.
• Do not switch the application to WebFlux to get concurrency.
• Do not add a custom TaskExecutor, VirtualThreadTaskExecutor, or Executors.newVirtualThreadPerTaskExecutor() bean unless the product needs a named executor beyond Spring Boot's default.
• Do not lower server.tomcat.threads.max as a virtual-thread trick unless you are measuring a specific experiment.

Forbidden

• Never omit spring.threads.virtual.enabled: true from a real servlet/MVC app.
• Never place that flag only in application-development.yml or only in application-production.yml.
• Never introduce WebFlux solely to handle blocking I/O concurrency.
• Never add a custom virtual-thread executor as the application's default request concurrency mechanism.
• Never require a Tomcat max thread override to "enable" virtual threads.