2012-09-25

This describes an experimental implementation of a simple protocol for communications between a number of servers (daemons) organized in a full mesh and one or more clients external to the ring.

For historical reasons the daemon is called zog and its Python implementation pzog. There is a client called sprog; its Python implementation is of course psprog.

Participants send messages, simple strings, to one another using tcp/ip, one of the standard Internet protocols.

Daemons log all messages to either access.log or error.log, with CRLF terminated messages of reasonable length (<512 bytes) being logged to access.log and all other messages reported to error.log.

Daemons also listen for traffic from clients on port 55552.

For the purpose of this exercise, the ring consists of five machine with addresses in private address space, 192.168/8

• MV, 192.168.152.242
• PA, 192.168.152.252
• G, 192.168.152.254
• LA, 192.168.152.253
• S, 192.168.152.11

The pzog daemons are built using a daemon specification first set out here, later to be split off as a separate github project.

Clients run psprog, which talks to the pzog daemons on port 55552. At least one psprog client will run. By default the client will send messages at configurable intervals to a randomly selected server. Command line switches will be available to change this behavior, to round-robin (-r/--roundRobin) or to target a specific host (-s/--specificHost). If the testing option is chosen, specificHost will be 127.0.0.1.

The default interval should be 10s.

Pzog messages are simple strings, Unicode encoded as UTF-8.

In this implementation, messages are standard Python strings preceded by a single digit, the wrapping* byte.

The wrapping byte will be one of 0, 1, or 2. That is, it will be a single ASCII character.

Content will be quasi-random with lengths (-i/--interval) in the range [32..63] inclusive, not counting the 'wrapping' byte. Content will consist of printing characters. [Content length should be adjusted as necessary to keep log lines within 80 characters.]

On receiving a message other than a keep-alive from a client, a server will forward it to its '+1' and +2 peers with '+1' and +2 wrappings respectively.

On receiving a message from a peer, a server will examine its envelope. All messages will be logged AFTER any forwarding.

If the wrapping is zero, the message will just be logged. If the wrapping is '+1', the message will be forwarded to the peer's +3 server with a zero wrapping. If the wrapping is +2, the message will be forwarded to the +4 server with a zero wrapping.

On receiving a message from a client which is other than a keep-alive a server will forward it to its '+1' and +2 peers with a +2 wrapping in each case.

If the wrapping is zero, the message will just be logged.

If the wrapping is '1', the message will be forwarded to the receiver's '+1' peer with a zero wrapping. [We will not use this wrapping in the current configuration.]

If the wrapping is 2, the message will be forwarded to the receiver's +2 peer with a zero wrapping.

pzog protocol should be org.xlattice.pzog and should at this point define two message pairs: keepAlive and ack, and data and ok.

Pre-Alpha. Partial (well, skeletal) implementation exists but is untested.

More information on the pzog project can be found here