A Minecraft server is not a short term job.

I guess it can be in a specific case: minigames servers (such as Hypixel), which are just a bunch of servers "connected" together. Players start into a "lobby" server, where they can choose a minigame, and are then sent to another server where they spend a few minutes.

The game servers don't restart after the end of a round, though, do they? I'd imagine they kick the players back to the lobby, reset the in-server game, and then tell the lobby to send the next batch of players.

You assume that load is constant, it isn't. And load varies not only with amount of players on minigames server, but with changes in distribution of players between minigames also.

There's usually more than one server per minigame. You could see it in the url you were redirected to; they had more servers running the more popular minigames. Each minigame has a player limit, so the maximum load on any given minigame server is known (within the bounds of the minecraft sub-superset that makes up that minigame- but usually the minigames are deliberately limited/bounded in how much computation they need, as opposed to vanilla Minecraft). Extra players get sent to the next available server. If there's consistent overflow, at that point you might turn on a whole new server, or change a server's gamemode (I don't know to what degree Hypixel actually did/does this, or how often it's actually necessary).

This is fairly certainly how it used to be done. Besides, you can have the server idle a good bit before actually letting players in.

The JVM can start up in less than 0.1 seconds. Depending on the amount of classes being loaded it is not an issue even for lambda and k8s jobs.

The VM starts up plenty fast. The slow part is when people use reflective dependency injection containers that take seconds to scan the class path before before executing.

This is why frameworks like Micronaut exist.

Micronaut, Quarkus, Avaje Inject, CDI Lite. Plenty of solutions if people would stop reaching for Spring.

You clearly did not deploy enough classes on Lambda to have more than 10 seconds warmup on a trivial Java based Lambda function.

Warm-up is more a function of invocation count rather than time as you seem to be suggesting here

This is a Minecraft server, so it's going to be running 24/7.

I see you aren't familiar with modern state of Minecraft servers. Due to Minecraft being limited to a one core big servers actually aren't a single instance. They use proxy servers(such as BungeeCord and it's forks) which distributes load between several lobby servers and from there people join one of custom gamemodes(Skyblock, Bedwars, etc). This allows for tens of thousands of people to play simultaneously, but not in the single world, while SMP(Survival Multiplayer) servers can run couple of hundreds at most. These giant servers are heavily containerized and automatically scale under load, so spinning up and shutting down servers is a pretty normal thing. And there have been some attempts to make Minecraft to run a single world on multiple instances(MultiPaper and some private ones), so even for usual SMP server it can be a commonplace soon as player join and leave.

> And there have been some attempts to make Minecraft to run a single world on multiple instances(MultiPaper and some private ones)

First time I hear about MultiPaper, another idea I had which I din't know someone was already working on LOL. It's a pretty promising idea considering the current performance problems of the game. This could possibly allow thousands of players in the same server which would be AMAZING, almost a completely different game. Imagine if MultiPaper was compiled to native using GraalVM.

I encourage my competitors to keep thinking this.