FRμIT is an academic project that looks at building and connecting micro-data-centres together, and what can be achieved with this kind of architecture. Currently they have hundreds of Raspberry Pis and they’re aiming for 10,000 by the project end. They invited us to join them, we’ve already solved the problem of building a centralised Raspberry Pi data centre and wanted to know if we could advise and assist their project. We recently joined them in the Cambridge University Computer Lab for their first project meeting.
Currently we centralise computing in data centres as it’s cheaper to pick up the computers and move them to the heart of the internet than it is to bring extremely fast (10Gbps+) internet everywhere. This model works brilliantly for many applications because a central computing resource can support large numbers of users each connecting with their own smaller connections. It works less well when the source data is large and in somewhere with poor connectivity, for example a video stream from a nature reserve. There are also other types of application such as Seti@Home which have huge computational requirements on small datasets where distributing work over slow links works effectively.
Gbps per GHz
At a recent UK Network Operator Forum meeting, Google gave a presentation about their data centre networking where they built precisely the opposite architecture to the one proposed here. They have a flat LAN with the same bandwidth between any two points so that all CPUs are equivalent. This involves around 1Gbps of bandwidth per 1GHz of CPU. This simplifies your software stack as applications don’t have to try and place CPU close to the data but it involves an extremely expensive data centre build.
This isn’t an architecture you can build with the Raspberry Pi. Our Raspberry Pi cloud is as about as close as you can manage with 100Mbps per 4×1.2GHz cores. This is about 1/40th of the network capacity required to run Google architecture applications. But that’s okay, other applications are available. As FRμIT scales geographically, the bandwidth will become much more constrained – it’s easy to imagine a cluster of 100 Raspberry Pis sharing a single low bandwidth uplink back to the core.
This immediately leads to all sort of interesting and hard questions about how to write a scheduler as you need to know in advance the likely CPU/bandwidth mix of your distributed application in order to work out where it can run. Local data distribution becomes important – 100+ Pis downloading updates and applications may saturate the small backbone links. They also have a variety of hardware types, the original Pi model B to the newer and faster Pi 3, possibly even some Pi Zero W.
We took the members of the project through our Raspberry Pi Cloud is built, including how a Pi is provisioned, how the network and operating system are provisioned and the back-end for the entire process from clicking “order” to a booted Pi awaiting customer login.
In discussions of how to manage a large number of Federated Raspberry Pis we were pleased to find considerable agreement with our method of managing lots of servers: use OpenVPN to build a private network and route a /48 of IPv6 space to it. This enables standard server management tools work, even where the Raspberry Pis are geographically distributed behind NAT firewalls and other creative network configurations.
Donate your old Pi
If you have an old Raspberry Pi, perhaps because you’ve upgraded to a new Pi 3, you can donate it directly to the project through PiCycle. They’ll then recycle your old Raspberry Pi into the distributed compute cluster.
We’re looking forward to their discoveries and enjoyed working with the researchers. When we build solutions for customers we’re aiming to minimise the number of unknowns to de-risk the solution. By contrast tackling difficult unsolved problems is the whole point of research. If they knew how to build the system already they wouldn’t bother trying.