Diablo II: Resurrected Outages: An explanation, how we’ve been working on it, and how we’re moving forward

Hello, everyone.

Since the launch of Diablo II: Resurrected, we have been experiencing multiple server issues, and we wanted to provide some transparency around what is causing these issues and the steps we have taken so far to address them. We also want to give you some insight into how we’re moving forward.

tl;dr: Our server outages have not been caused by a singular issue; we are solving each problem as they arise, with both mitigating solves and longer-term architectural changes. A small number of players have experienced character progression loss–moving forward, any loss due to a server crash should be limited to several minutes. This is not a complete solve to us, and we are continuing to work on this issue. Our team, with the help of others at Blizzard, are working to bring the game experience to a place that feels good for everyone.

We’re going to get a little bit into the weeds here with some engineering specifics, but we hope that overall this helps you understand why these outages have been occurring and what we’ve been doing to address each instance, as well as how we’re investigating the overall root cause. Let’s start at the beginning.

The problem(s) with the servers:

Before we talk about the problems, we’ll briefly give you some context as to how our server databases work. First, there’s our global database, which exists as the single source of truth for all your character information and progress. As you can imagine, that’s a big task for one database, and wouldn’t cope on its own. So to alleviate load and latency on our global database, each region–NA, EU, and Asia–has individual databases that also store your character’s information and progress, and your region’s database will periodically write to the global one. Most of your in-game actions are performed against this regional database because it’s faster, and your character is “locked” there to maintain the individual character record integrity. The global database also has a back-up in case the main fails.

With that in mind, to explain what’s been going on, we’ll be focusing on the downtimes experienced between Saturday October 9 to now.

On Saturday morning Pacific time, we suffered a global outage due to a sudden, significant surge in traffic. This was a new threshold that our servers had not experienced at all, not even at launch. This was exacerbated by an update we had rolled out the previous day intended to enhance performance around game creation–these two factors combined overloaded our global database, causing it to time out. We decided to roll back that Friday update we’d previously deployed, hoping that would ease the load on the servers leading into Sunday while also giving us the space to investigate deeper into the root cause.

On Sunday, though, it became clear what we’d done on Saturday wasn’t enough–we saw an even higher increase in traffic, causing us to hit another outage. Our game servers were observing the disconnect from the database and immediately attempted to reconnect, repeatedly, which meant the database never had time to catch up on the work we had completed because it was too busy handling a continuous stream of connection attempts by game servers. During this time, we also saw we could make configuration improvements to our database event logging, which is necessary to restore a healthy state in case of database failure, so we completed those, and undertook further root cause analysis.