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updated Federation.md

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@ -8,31 +8,31 @@ To enhance resilience in terms of backup and fail-over, also for load-balancing,
### Form a Federation ### Form a Federation
To form a federation, multiple supernodes need to be aware of each other. To get them connected, additional `-l` option from CLI is required at the supernode. To form a federation, multiple supernodes need to be aware of each other. To get them connected, an additional `-l` option from command line is required at the supernode.
This option takes the IP address (or name) and the UDP port of a known supernode, e.g. `-l 192.168.1.1:1234`. This option takes the IP address (or name) and the UDP port of another known supernode, e.g. `-l 192.168.1.1:1234`.
### Use a Federation ### Use a Federation
Federated supernodes take care of propagating their knowledge about other supernodes to all other supernodes and the edges. Federated supernodes take care of propagating their knowledge about other supernodes to all other supernodes and the edges.
So, edges only need to connect to one supernode (called anchor supernode), using `-l` option. That supernode needs to be present at start-up. So, in the first place, edges only need to connect to one supernode (called anchor supernode) using `-l` option. This supernode needs to be present at start-up.
Optionally, more anchor supernodes of the same federation can be provided to an edge using several `-l` options. This will counter scenarios with less assured initial supernode availability. Optionally, more anchor supernodes of the same federation can be provided to an edge using several `-l` options. This will counter scenarios with reduced assured initial supernode availability.
## How It Works ## How It Works
Supernodes should be able to communicate among each other as regular edges already do. For this purpose, a special community called federation was introduced. Federation provides mechanisms to connect the supernodes of the network, and enhance backup, fail-over and load-sharing, without any visible behavioral change. Supernodes should be able to communicate among each other as regular edges already do. For this purpose, a special community called federation was introduced. The federation feature provides some mechanisms to inter-connect the supernodes of the network enhancing backup, fail-over and load-sharing, without any visible behavioral change.
The default name for the federation is `*Federation`. Internally, a madnatory special character is prepended to the name: that way, an edge won't be able to provide a regular community with the same name of the federation. Optionally, a user can choose a federation name (same on all supernodes) and provide it via `-F mySecretFed` option to the supernode. Alternatively, the federation name can be passed through the environment variable `N2N_FEDERATION`. The default name for the federation is `*Federation`. Internally, a mandatory special character is prepended to the name: that way, an edge won't be able to provide a regular community with the same name of the federation. Optionally, a user can choose a federation name (same on all supernodes) and provide it via `-F mySecretFed` option to the supernode. Alternatively, the federation name can be passed through the environment variable `N2N_FEDERATION`.
Federated supernodes register to each other using REGISTER_SUPER message type. The answer, REGISTER_SUPER_ACK, contains a payload with informations about other supernodes in the network. Federated supernodes register to each other using REGISTER_SUPER message type. The answer, REGISTER_SUPER_ACK, contains a payload with information about other supernodes in the network.
This specific mechanism is used also during the registration process happening between edges and supernodes, so edges are able to learn about other supernodes. This specific mechanism is also used during the registration process taking place between edges and supernodes, so edges are able to learn about other supernodes.
Once edges have saved this information, it is up to them choosing the supernode they want to connect. Each edge pings supernodes from time to time and receives information about them inside the answer. We decided to implement a work-load based selection strategy because it is more in line with the idea of keeping the workload low on supernodes. Moreover, that way the entire load of the network is distributed evenly among all available supernodes. Once edges have received this information, it is up to them choosing the supernode they want to connect to. Each edge pings supernodes from time to time and receives information about them inside the answer. We decided to implement a work-load based selection strategy because it is more in line with the idea of keeping the workload low on supernodes. Moreover, this way, the entire network load is evenly distributed among all available supernodes.
An edge connects to the supernode with the lowest work-load and it is re-considered from time to time, with each re-registration. We used a stickyness factor to avoid too much jumping between supernodes. An edge connects to the supernode with the lowest work-load and it is re-considered from time to time, with each re-registration. We use a stickyness factor to avoid too much jumping between supernodes.
Thanks to this feature, n2n is now able to handle security attacks such as DoS against supernodes and it can redistribute the entire load of the network in a fair manner between all the supernodes. Thanks to this feature, n2n is now able to handle security attacks such as DoS against supernodes and it can redistribute the entire load of the network in a fair manner between all the supernodes.