Discord rewrote their stack multiple times.

Not because they got it wrong.

Because they got too big for what they built.

2013 — The starting stack

Elixir for real-time messaging. Python for APIs. Go for microservices. MongoDB for storage. Electron for desktop.

Standard startup choices. Ship fast, figure out the rest later.

2017 — MongoDB had to go

5 million users. MongoDB couldn't keep up.

Switched to Cassandra . 12 nodes. Worked fine.

Until 2022, when those 12 nodes became 177. Maintenance got painful. Costs climbed. They moved to ScyllaDB .

One problem. Nine years. Three databases.

2019 — Elixir wasn't fast enough for everything

Sorting large data sets in Elixir was taking 170ms per operation.

At Discord's scale, that's not acceptable.

They rewrote it in Rust . Dropped to 1ms .

That's it. That's the whole reason.

2020 — Go's garbage collector became the enemy

Discord's Read States service tracks every message you've read.…