Micronaut 3, which was in Grails 5/6 not sure of the minor versions, but it did have support for WebSockets, just not sure if that feature is usable from Grails or not because I haven't tried it: https://micronaut-projects.github.io/micronaut-docs-mn3/3.0.0/guide/index.html#websocket Also even if it did work locally, who knows if it would work if you built to a war. Personally, I haven't built to a war in quite some time, because of the benefits of building to a Jar.