Cloud Computing – Mind your WAN connection!

The last couple of years i’ve been involved in some projects regarding Cloud Computing and had to face with performance issues at some of these clients. The situations were almost identical;

– Customer switched from client-server to Cloud Computing (Citrix or something similar)
– Existing internet configuration is used and/or extended
– All application- and performance tests (performed by the client) looked fine but when in production the performance is extremely poor.

In almost all of these cases the client had already made calculations of there own;

– Calculating with +/- 75kbit/s of bandwidth per active user
– Idle users do not use traffic (assuming)
– All traffic is going over the WAN connection to the Data Center

I hate to spoil it but they were dead wrong.

It’s very well possible that one user, with only one session, consumes all available WAN bandwidth. Just start a browser and go to or scroll on a page that has ugly advertisement screaming at you. Also you will see that when scrolling through a page all bandwidth is consumed by this session. At this time, all other colleagues are pulling out there hairs and strolling to the IT Department like a bunch of zombies. Trust me, they will, i’ve seen it happen.

Each office should have a router with bandwidth monitoring options such as netflow, sFlow or SNMP in order to investigate the actual usage of sessions, specially in the morning when everybody wants to log in at the same time. If you don’t have any tools for this simply download MRTG or Cacti (opensource).

The second item that is always forgotten; it’s not only ICA traffic going over the WAN connection consuming bandwidth! Most company’s have big multi-functional printers and scanners at there offices – When somebody hits the CTRL+P (print) this will go over the WAN pipe, back in! This would mean that when somebody has a big file (let’s say 50MB?) that they want to print this will be pushed in over the WAN connection at the maximum possible speed.

A few things to look at when migrating to a cloud situation;

– Run calculations with +/- 120-150kbit/s for each session
– Do not assume sessions are not taking bandwidth when idle
– Monitor the current printserver and actual logged in user to get an estimate
– Calculate the required WAN bandwidth and setup QOS/Bandwidth limitations for printing/session usage.


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