[alicewales]

It's hardly surprising. Everything on the UK internet goes through London anyway. If you have a DC in Manchester and an end-user in Liverpool, the link normally goes Manchester - London - Liverpool.

It's not a great situation, having everything so centralised on London, but it's a small enough country that it doesn't have a huge effect on latency. It would make no sense for AWS to locate in a non-London region when everything would then have to be backhauled to London.

[Symbiote]

A 10 year old PDF map [1] shows plenty of other fibre connections. Does everything really go through London?

Locating outside London would be a lot cheaper, for labour, land and power.

[1] http://www.globalcrossing.com/docs/fn/tanet-uk-map.pdf

[alicewales]

There is fibre outside London, but most of the main end-user ISPs have just the one POP and it's normally in Docklands. Everything ends up going through there one way or another.

[inopinatus]

Not every decision is about cost minimisation. There's a resiliency motivation to place DCs in separate flood plains and separate power grids if possible. Whether AWS is following that, I cannot say.

[jeffbarr]

We (I am part of the AWS team) pay a lot of attention to that; our "Overview of Security Practices" paper[1] says:

"Each availability zone is designed as an independent failure zone. This means that availability zones are physically separated within a typical metropolitan region and are located in lower risk flood plains (specific flood zone categorization varies by Region). In addition to discrete uninterruptable power supply (UPS) and onsite backup generation facilities, they are each fed via different grids from independent utilities to further reduce single points of failure. Availability zones are all redundantly connected to multiple tier-1 transit providers."

[1] https://d0.awsstatic.com/whitepapers/aws-security-whitepaper...

[walshemj]

London does have food risk back in the 80's when I worked for British Telecom we moved our central London DC(next to London bridge station) out to Add to crickelwood for that reason.

Of course later on the IRA bombed the building next door to us - we survived ok the modems just rest them selves

[philsnow]

I've always assumed that availability zones would not necessarily be in the same building or even site in a given region, but something I've wondered is what does the network look like between zones?

Does inter-AZ traffic traverse only fiber that you wholly own? Does AWS send traffic over some shared links in some cases? If only some cases, which cases?

[dastbe]

James Hamilton gives a good talk that goes over networking (and more). This is it from reinvent 2014.

https://m.youtube.com/watch?v=JIQETrFC_SQ

[dgemm]

I would assume they wouldn't put any DC on a flood plain.

[jonknee]

People like to live near water and where it rains.