The server tech that saved WoW 10 years ago is causing problems for Classic's Season of Discovery, dev reveals: 'a layer is actually just sharding with a lot of sticky tape'

The second season of WoW classic's Season of Discovery (SoD) is live—and the layers are acting up again, this time in Stranglethorn Vale (STV). For the uninitiated, this season brings Blood Moons to STV: 30-minute PvP brawls that tick around every three hours. The main issue? The bouncers at the door aren't great at their jobs.

SoD's server infrastructure runs on layers, which are meant to chop up the server load and keep things running nicely. Ideally, players engaging in these large-scale PvP events would let the layer system plonk them somewhere with a balanced amount of players. 

In reality, they've been shuffling into different layers on purpose by grouping up, leading to what one dev describes as a «gross» user experience. Senior game producer Tom Ellis took to Twitter to go over the technical details this weekend (thanks, WoWHead). As he notes, layering actually has its roots in a system which pulled World of Warcraft out of the fire 10 years ago, despite putting SoD in hot water now.

«Once upon a time, a realm ran one copy of each zone locally on its own hardware … it was all running in the same place, you could kite mobs across zones, escort quests had NPCs pathing across zone boundaries,» Ellis writes. «As hardware improved and performance improvements were made, expansion after expansion we raised the cap on the number of concurrent players we allowed to log in.»

This caused major problems however, when the CPU cores started to struggle under high loads. «This all came to a head in Warlords of Draenor when in the face of a very successful launch the starting zones in WoD were completely unable to handle the load they faced.» Ellis outlines how a former Blizzard developer spent «three days and nights (we don't condone that sort of behaviour anymore!)» developing what's now known as sharding technology.

«It made the game feel less cohesive, but it meant the realm cap and zone capacity were now disconnected entirely, it also gave us the ability to have