How to make an RLCraft server

RLCraft is the most downloaded modpack there is: nearly 30 million downloads on CurseForge. Its promise is simple — make Minecraft "unfairly difficult" — and its consequences on a server are less so. Here's what actually changes when you host it for a group.

What RLCraft does to the game, and why that matters in multiplayer

This isn't a pack that adds machines: it's a pack that removes safety nets. Its authors describe it as an "incredibly hardcore and semi-realism challenge revolving around survival, RPG elements, and adventure-like exploration":

• thirst and temperature — two more gauges to watch, constantly;
• food no longer heals — passive regeneration is switched off;
• progression is gated by skills: you can't use a piece of equipment before unlocking it;
• heavily reworked mobs and dungeons, including dragons and aggressive wildlife that prowls at night.

Solo, dying often is part of the deal. In a group, it changes the server's dynamic: nobody "catches up" in one evening, and a player joining three weeks in starts a very long way back. That's the one real piece of group advice for this pack: start together, or accept that newcomers are playing a different game.

Version and Java: RLCraft lives on 1.12.2

RLCraft targets Minecraft 1.12.2 (and 1.11.2) on the Forge loader. That isn't an archival detail: it's a generation of Minecraft older than most modern packs, with its own requirements.

The Java version is tied to the Minecraft version — the Minecraft Wiki asks for Java 17 from 1.18 and Java 21 from 1.20.5, and "a Java runtime (JRE), version 8 or higher" for earlier versions like this one. If you're self-hosting, that's the first trap: a Java picked at random won't start a pack of this generation.

Here, you choose nothing: the loader and the Java version are derived from the pack.

RAM: its authors give the figure, and it's about the heap

RLCraft is one of the few packs to state its need plainly. Its page recommends "allocating 3 to 4GB's of RAM", with example arguments showing -Xmx4G.

But -Xmx is the JVM heap — not the machine's memory. The operating system, Docker and Java's off-heap memory live beside it. Here, the heap is the smaller of "RAM − 2 GB" and "75% of RAM":

In other words: take the 8 GB tier. The 4 GB tier yields only a 2 GB heap, less than the pack asks for itself — and the creation screen will warn you, because it compares heaps, not machine sizes.

CPU, for a reason specific to this pack

RLCraft fills the world with creatures: dragons, giant insects, nocturnal wildlife. Every living entity has to be simulated twenty times a second, and a base under attack at night can concentrate a great many in one place.

The symptom is recognisable: the server doesn't fall over, it drags — hits land late, mobs teleport. If the heap is comfortable and it happens anyway, it's the processor: the dedicated CPU level is the only change that answers it.

Conversely, a server that dies when a player wanders away from spawn is a heap problem, not a CPU one: generating chunks is the most memory-hungry thing it does.

The settings that genuinely matter here

On a pack this punishing, two settings change the experience more than all the others:

• Simulation distance (3 to 32, default 10): the radius in which the server keeps the world — and therefore the mobs — alive. Dropping it to 6 or 8 is the cheapest fix for lag, and on RLCraft it has a visible effect, because there's a great deal to simulate.
• The whitelist: RLCraft attracts the curious, and an open server on a weeks-long hardcore run is a bad idea. Add your group's usernames.

PvP deserves an explicit decision before you start, too: on a pack where dying is expensive, it isn't something you switch on "to see".

The first boot, and your saves

Expect 15 to 25 minutes on first boot: downloading the pack, resolving mods, then generating a world stuffed with added structures. Later boots are quick. Don't kill it thinking it failed — that's the most common phantom failure on big packs.

After that, the world is archived before every shutdown, with a save-all flush immediately before, and restored on the next boot. An automatic backup runs every 30 minutes while you play, of which the last 5 are kept.

On RLCraft that last line matters more than elsewhere: a run represents dozens of hours of skill-gated progression, and it doesn't get redone over a weekend.

What not to do

Switch packs on an RLCraft world. The world holds thousands of blocks and entities Minecraft has never heard of; loaded without its mods, it loses them permanently. To try something else, create a second server.

Move up a major version. RLCraft is a 1.12.2 pack; there's no upgrade path to a newer generation that preserves the run.

Create your Minecraft server and pick RLCraft from the modpack list. Your first session is free.