I have a pet project that I’ve written in Grails 3. I run it on an already-busy cloud server via the fat jar. I kept the default Tomcat configuration but soon I kept getting out of memory errors. I wanted to use something more lightweight. So I started looking how to change out Tomcat for something else in Grails 3, but I couldn’t find anything. But Grails 3 is just Spring Boot, right?

I found this page on in the Spring Boot docs about changing from Tomcat to Undertow. I’ve used Undertow before and I really liked it. The documentation didn’t quite match what I had in my build.gradle file but it was really pretty easy. I simply changed this line:compile "org.springframework.boot:spring-boot-starter-tomcat"

to this:compile "org.springframework.boot:spring-boot-starter-undertow"

And that was it — I recompiled and redeployed… and haven’t had a memory problem since. That was two months ago. The only difference I’ve seen is that dbconsole doesn’t work while running in development mode, but that’s not a big deal to me.