Introduce the concept of metanodes

updates the README file, and makes the post-merge script read the
metanodes file instead of the whole hosts/ directory.

README.md

@@ -1,6 +1,68 @@
 [![Build Status](https://travis-ci.org/freifunk/icvpn.svg?branch=master)](https://travis-ci.org/freifunk/icvpn)
 
-This repository holds IC-VPN keys and configuration.
+This repository contains the tinc hosts for ICVPN-Peers and several helper scripts.
+
+## Setup
+
+This network requires the use of the Tinc VPN Daemon. You should use at least version 1.0.24 or higher, als the
+current pre-release version 1.1pre11 seems to work just fine.
+
+### Clone the repository
+    cd /etc/tinc/
+    git clone https://github.com/freifunk/icvpn.git
+    cd icvpn
+    cp scripts/post-merge .git/hooks/
+
+### Create your tinc configuration
+
+Open your favorite editor and create the /etc/tinc/icvpn/tinc.conf.
+    Name=entenhausen1
+    Mode=switch
+More options can be found through
+    man tinc.conf
+Afterwards create a keypair with tincd.
+    tincd -n icvpn -K
+Hint: In version 1.1 this option was moved to the tinc binary and is called <code>generate-rsa-keys</code>.
+
+### Execute post-merge hook
+
+This step is necessary to populate your new configuration with infos about the metanodes.
+    ./git/hooks/post-merge
+
+### Set up a cronjob to update the repository in regular intervals.
+
+    @daily cd /etc/tinc/icvpn/; git pull > /dev/null
+
+## What are meta nodes?
+
+Tinc has a ConnectTo configuration option that describes which peers on startup to connect *and* sync metadata to.
+
+Until now (2015/4) we had roughly 74 nodes, and every node connected to each other (full mesh). Tinc however 
+does not scale this way, because on each connect and disconnect all ConnectTo-lines are being notified of this
+and then notify their neighbours again. Many smaller nodes seemingly could not handle the amount of metadata generated 
+by this which resulted in TCP Zero Windows. They then disconnected, and reconnected, producing more metadata in
+the process, which was followed by even larger nodes queueing up metadata, which resulted in all nodes taking
+a massive cpu and memory hit. Memory usage of up to 1.5GB was spotted, accumulated in less than 12 hours.
+
+However for tinc to build its network graph it is sufficient, if all nodes only exchange metadata at a few nodes,
+which results in much less strain on the whole network. This is why we now use meta nodes, which are defined in
+the `./metanodes` file.
+
+Criteria for the selection of meta nodes are:
+1) autonomous system diversity
+2) community diversity
+3) ample resources (cpu, memory, traffic)
+
+When data needs to be transferd between two nodes, this will happen indepently of those meta nodes. Through the shared
+network graph a direct transfer is possible and will be tried: at first via UDP, then via TCP, then indirectly. While
+indirect routing is possible the meta nodes are not required to provide forwarding for those packets.
+
+## Contact
+
+The maintainers can be reached at
+- [icvpn@lists.funkfeuer.at](mailto:icvpn@lists.funkfeuer.at)
+- [irc.hackint.org #icvpn](irc://irc.hackint.org/icvpn)
+
+We have set up IRC notifications for all repositories concerning the icvpn network.
 
-For more Info see http://wiki.freifunk.net/IC-VPN
 

metanodes

@@ -0,0 +1,4 @@
+berlin2
+darmstadt2
+luebeck2
+trier1

scripts/post-merge

@@ -18,12 +18,12 @@ test -w $TINCCFG || fail "ERR: $TINCCFG is not writeable"
 
 sed -i '/^ConnectTo/d' $TINCCFG
 
-for HOST in hosts/*; do
+while read HOST; do
   # skip hosts without address
-  grep -iq '^Address' -- "$HOST" || continue
+  grep -iq '^Address' -- hosts/"$HOST" || continue
 
-  echo "ConnectTo = ${HOST##*/}" >> $TINCCFG
-done
+  echo "ConnectTo = $HOST" >> $TINCCFG
+done < metanodes
 
 /usr/sbin/invoke-rc.d tinc reload icvpn