--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/README.md	Fri Oct 07 20:44:41 2016 +0200
@@ -0,0 +1,48 @@
+# clusterconsensus
+
+A library implementing a replicated state machine with generic state machine, transport and state changes.
+
+For example, a using application could use this package with protocol buffers, leveldb and gRPC; and another
+one might use JSON, in-memory state and HTTP.
+
+## Protocol
+
+The protocol is a custom Paxos implementation. It works like this, basically:
+
+### Bootstrapping
+
+* A set of participants is started. Participant `A`'s `ConsensusServer` receives a StartParticipation request.
+  This request is `StartParticipation(0, 0, Member{addr: "A"}, [Member{addr: "A"}], []byte{})` (i.e., an empty
+  StartParticipation request)
+* Now one participant is running, and sees that it itself is the master. It now finds out in some way which other
+  participants to add, and calls `AddMember()` on itself. The library will arrange a process by which a new member
+  is added to the consensus round.
+* Repeat this for other members
+
+### Normal operation
+
+We assume that the current instance is 12, and the sequence number in that instance is 34.
+
+* One participant wants to modify the state. It calls `Submit()` on the `Participant` with one or more changes.
+* If the Participant is not master, it will send the request to the master using the `Submit()` method on the stub.
+* If the Participant is the master, or has received a `Submit` request, it will proceed by coordinating the change.
+* First, all non-master participants are sent `Accept(12, 35, []Change{ *some change* })`.
+* This leads to the non-master participants *staging* that change.
+* The next time the master wants to apply a change, it sends `Accept(12, 36, []Change{ *some new change* })`. This leads
+  to non-master participants "committing" (i.e. applying) all staged changes before sequence `36` to the state machine.
+
+### Master has crashed
+
+Current instance: 22 Current sequence: 44
+
+* A participant, "B", wants to modify the state, but can't reach the master to `Submit()` a change. It proceeds by
+  becoming a candidate. It sends `Prepare(23, Member{ addr: "B" })` to all known members. If a majority replies within
+  the deadline with a positive vote, then the `B` is the new master.
+* In order for all participants to know about this change, `B` submits a request `Accept(23, 1, []Change{})` which confirms
+  the previous `Prepare()` call (because of the new instance in the `Accept` request)
+* Now everyone knows of the new master, and the cluster continues in *Normal operation*.
+
+### Adding/removing members
+
+* Membership changes are relatively straight-forward; they are just special changes that don't use `Accept()`, but rather
+  the `AddMember()` and `RemoveMember()` methods in `ParticipantStub`.