Canonical Introduces "Fan" For Container-To-Container Networking
Written by Michael Larabel in Ubuntu on 22 June 2015 at 09:40 AM EDT. 5 Comments
Mark Shuttleworth this morning announced Fan: their solution to container-to-container networking.

For handling container networking most use an overlay approach, which Mark described as, "You make a database in the cloud to track which IP address is attached to which container on each host VM. You then create tunnels between all the hosts so that everything can talk to everything. This works, kinda. It results in a mess of tunnels and much more complex routing than you would otherwise need. It also ruins performance for things like multicast and broadcast, because those are now exploding off through a myriad twisty tunnels, all looking the same."

Mark went on to describe the fan approach, "It’s called [fan] because you can picture it as a fan behind each of your existing IP addresses, with another 250 IP addresses available. Anywhere you have an IP you can make a fan, and every fan gives you 250x the IP addresses. More than that, you can run multiple fans, so each IP address could stand in front of thousands of container IP addresses. We use standard IPv4 addresses, just like overlays. What we do that’s new is allocate those addresses mathematically, with an algorithmic projection from your existing subnet / network range to the expanded range. That results in a very flat address structure – you get exactly the same number of overlay addresses for each IP address on your network, perfect for a dense container setup. Because we’re mapping addresses algorithmically, we avoid any need for a database of overlay addresses per host. We can calculate instantly, with no database lookup, the host address for any given container address. More importantly, we can route to these addresses much more simply, with a single route to the “fan” network on each host, instead of the maze of twisty network tunnels you might have seen with other overlays."

Mark explains more details of Fan on his blog. Canonical's Dustin Kirkland also wrote a blog post about this new container-to-container networking approach with much more technical information. Fan will be landing soon in Ubuntu 15.10 while patches will be backported for Ubuntu 15.04 and 14.04 LTS. They're also working on an "RFC" to propose their networking approach to other operating systems and for it to be adopted by the container world.
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