Additional instances cannot be launched, please try again later.Ok, we all know this by now, or if you don't see what it is, you're really only playing solo, and never put a foot into instances for months.
Since a few patches Blizzard decided to put a limit on the number of instances up at the same time on their instance server. If the goal is reached, which is to prevent horrible lag during raids, that we experienced during the early months of Lich King and were driving us crazy on boss fights like Thaddius. The side effect is that a lot of us can't enter instances, or have to wait sometimes half an hour, mindlessly trying to enter an instance to be able to play into it.
Instances limit & patch 3.2
Some will say I'm qqing, and that Blizzard has already said they are aware of that problem and are trying to solve it. But still, I can only see it as a very bad commercial/design choice to release patch 3.2 that is obviously sending back everyone into instances, before they fixed that problem.
Nowadays I don't even try to play when I'm back from work, between 7pm and 9pm it's just too tedious to try going into an instance and I'm not really fond of going back and forth (or strafing left/right for the fast paced ones) for 15-20mn before being allowed to play.
Several computer for several game servers, but not as you could expect.
Each game server is separated onto several physical machines, Azeroth, Outland, Northrend and instances/raids are on 4 different computers, that group these world parts for several game servers (it's not clear if, for example, all the northrend parts of a whole battlegroup are on the same computer but it's the idea).
That will explain, if you didn't know it, why sometimes your world server (Northrend) is down while some of your guildies, or some of your alts can still play (in let say Azeroth).
That will also explain why it's not that easy to just "add some muscle" to the computer in charge of the instances to solve the problem. That's why Blizzard is saying it's complex and they need time.
Instance servers have a memory cap.
The problem seem obvious if you're a little into computer science. The instance server has a limit of hardware memory, when that limit is reached it has to "swap" his memory with virtual memory which is emulated on the hard-drive of the computer. The problem is that when it does that, the access time is about 100 to 1000 times slower on this "swapped memory", which is then producing server lags for the players in the affected instance. So, especially as Blizzard does not own the servers on which the game is played, the only solution they found is to limit the number of instances to avoid the memory swap problem.
They also installed a priority onto entering instances it's mostly LK raids > LK heorics > LK instances > older raids & instances. If you've tried to do a raid or vanilla instance during peak hours ... you're probably still trying :P
A temporary solution, instance queues.
What I'd like to see, as probably many people, is a queue. When you try entering an instance, you get into a queue and you're ported into your instance when it's your turn. Mostly what they did for Wintergrasp in the last patch.
This won't fix the problem, and they have to develop new code to be able to dynamically share several computer for the same "instance server" when needed. This is an obvious choice and necessity because all game servers don't have the same size, and the number of instances required by the players isn't at all the same during a day. But this type of coding is way more complex than the static allocation they are using right now, and it requires a lot more testing, what they are, I hope, doing right now.
Nevertheless, instance queues are a relatively simple to code patch that would make most of us much happier than the current situation. At least you can queue for your instance, and then go do your dailies for example instead or completely wasting your time trying to repeatedly enter the instance (because you have to do it if you ever want to play it ... which is what is driving me crazy).
You're all welcome to comment with your views and ideas on the instance cap. Not that Blizzard will ever read this blog, but I'll be curious to see if this problem is common to the US and the EU for example (as I think it is reading blogs & forums on both sides).