Fortnite hit a new peak of 3.4 million concurrent users this past weekend (Feb 3-4 2018) before suffering a major outage due to the high server demand.
Epic Games posted an article on the outage earlier today titled Postmortem Of Service Outage At 3.4M CCU that goes into some of the details on how the meltdown played out. The post goes into great detail on exactly which systems failed and how. Its all above my pay grade, but the article seems specifically aimed at a technical audience. Epic makes a pitch to potential employees at the start by asking for resume submissions. So if you know what a MongoDB shard is, be sure to take Epic Games up on their offer of employment!
The primary MCP database is comprised of 9 MongoDB shards, where each shard has a writer, two read replicas, and a hidden replica for redundancy. At a high level user specific data is spread across 8 shards, whereas the remaining shard contains matchmaking sessions, shared service caches, and runtime configuration data.
More importantly for the general audience is that Fortnite has now surpassed Playerunknown’s Battlegrounds in peak concurrent users. It may very well be the biggest PC and console game in the world right now!
Further Reading: Official Post