GNS Docker support

GNS3 Docker support

So the coding session for GSOC finally began this week. I got accepted with the GNS Docker support project and here is the project introduction and my plan of attack.

GNS3 is a network simulator that uses faithfully simulates network nodes. Docker is a highly flexible VM platform that uses Linux namespacing and cgroups to isolate processes inside what are effectively virtual machines. This would enable GNS3 users to create their custom virtual machines and move beyond the limitations of nodes that are network oriented and because of its lightweight implementation, would make it possible to run thousands of standalone servers on GNS3.
Right now GNS3 supports QEMU, VirtualBox and Dynamips (a Cisco IOS emulator). The nodes in GNS3 and the links between them can be thought of as virtual machines that have their own network stacks and communicate amongst themselves like separate machine on any other "real" network. While this is nice by itself, QEMU and VirtualBox are "slow" virtualization technologies because they provide full virtualization -> they can run any OS but this comes at a price. So while QEMU and VirtualBox can run various network services, it's not very efficient. Docker, on the other hand, uses kernel-level virtualization which means it's the same OS but processes are grouped together and different groups isolated between themselves, effectively creating a virtual machine. That's why Docker and other such virtualization solutions are extremely fast and can run thousands of GNS3 nodes -> no translation layer between host and guest systems because they run the same kernel. Docker is quite versatile when it comes to managing custom made kernel-based VMs. It takes the load of the programmer so he/she doesn't have to think about disk space, node startup, process isolation etc. Links between Docker containers pose an additional problem. In its current form, GNS3 uses UDP networking (tunnels) for all communication between all nodes. The advantage is that this is done in userland. It is very simple and works on all OSes without requiring admin privileges. However, using UDP tunnels has proven to be more difficult to integrate new emulators to GNS3 because they usually do not support UDP networking out of the box. OpenvSwitch is a production quality, multilayer virtual switch and interconnecting Docker containers and alleviating the problem of new emulators requires at least basic support for OpenvSwitch ports in GNS3. Additionally, this would enable Docker links in GNS3 to be manipulated through Linux utilities like netem and tc that are specialized for such tasks, something not possible with UDP tunnels.

Let's start coding!