How do you stream the audio to the people in the audience? Are you still using WebRTC or do you add some latency and use something like HLS? If WebRTC do you know the number of maximum listeners you can get to on the SFU?
We were able to serve 500-1000 participants from a mid-sized VPS a few weeks ago and were CPU constrained iirc so a beefier server should go further than that.
Spring Boot backed with Postgres and Maven to wrap it all up. Spring Boot is really years of distilled knowledge of creating web servers in Java. Its opinionated but for good reason; you'll very quickly get everything you need for a RESTful API and there's extensions for almost everything you'd need. Need to work with websockets? Just add a few lines to your POM. Need scheduling? Include an annotation on your main class. It really is a solid framework.
I don't understand the question, beyond the fact that Spring and Grails both had the same corporate sponsorship at one point in the past.
Spring Boot is a rapid, flexible, and fairly tight (as far as Java frameworks go) foundation for building Java applications. Grails is a Groovy-based wrapper layer around Spring and Hibernate.
So if you want to use Groovy for application development, then Grails is certainly there for you. However, I don't think it's the most competitive option. I think Groovy's great as a scripting language, and I use it for things like automated testing, but I wouldn't enjoy using it for primary application development because it's not a statically-typed language.
Although recent versions of Groovy allow you to designate typesafe "areas" within your code, it is still fundamentally non-typesafe. Because of this, tooling is always going to be weaker than it is for typesafe languages. IntelliJ is probably the best Groovy IDE out there, and it's still frustrating to work with because it can't detect autocomplete options most of the time.
If you're doing development on the JVM in the first place, then odds are you favor static typing. Plain Java, or Scala, or most of the fringe options like Kotlin or Ceylon. If you're in the minority camp who want to use a language with dynamic typing, even THEN there are better options than Groovy for application development. JRuby has a much broader and more active community, and Clojure will give you more "Internet cool points" on HN or Reddit or wherever.
Finally, the last time I looked at Grails, it was FAT. Building an application took forever. I'm sure they've (hopefully) optimized or rebuilt things since then. However, since it's a wrapper around Spring and Hibernate, it's never going be any lighter or faster than Spring and Hibernate.
I don't mean any disrespect to Groovy. I've been using it forever, and it comes in handy with certain use cases. However, it's primary niche is being the dynamic JVM language that most "enterprise" shops have become comfortable with... and so if you're trapped in an "enterprise" shop and are dying to use something other than plain Java, it's the thing you'd most likely be allowed to use.
