[Kimchi-devel] [RFC] discover Kimchi peers

[Sheldon]

I'd like to talk about how to discover Kimchi peers.

Now I just talk about  discover a peer in a same network here.

I will use a local multicast subnetwork address 
<http://en.wikipedia.org/wiki/Multicast_address#Local_subnetwork> to 
find peers in one network.
Choose 224.0.0.132 as the kimchi multicast address, and 8000 as the port.

For cross network  that need the router support multicast, so I give up 
discover a peer cross network.
I will let user add the remote peers manully.

In the whole system all peers are equal. There will not be a center 
discover service.

We will define two kinds of multicast message Notify and Search.
the format as follow.

         #  ____________________________________________
         # |        head       |  message body   | tail |
         # |___________________|_________________|______|
         # |sizeof(messageBody)|  json message   | EOL  |
         # |___________________|_________________|______|


the flow of  discover Kimchi peers:
1. one host multicast a "search" message. in this message it tell 
himself information, and ask others tell their information.
Like this:
{"search": {"domain": "kimchi-host1", "IP": "192.168.0.3", "httpport": 
"8000", "httpsport": "8001"}}
    this means "hello, I'm a kimchi host, this is my information, can 
you tell me who you are?"
2. others received a search will response an "notify" message.
Like this:
    {"notify": {"domain": "kimchi-host1", "IP": "192.168.0.3", 
"httpport": "8000", "httpsport": "8001"}}
     this tells others that "hi, I'm a kimchi host, I'm alive and this 
is my information"

o (user)  1 is "search"
/\  -------->                                        2 is "notify"
               | 1                        _____ ________________
     kimchi-host1 ------2-<---| DB |<----2-----|multicast listen |<--2--
                               |           |____| |_______________| 
         |
----------------------1------------------------------->  |
|
_____ |_____
|                 |
                                                              | switch     |
|                 |
|___________|
o   (user) |
/\  --------- -----------------------------2----------------------- --->|
               |             |            _____ ________________           |
     kimchi-host3 ------1<---| DB |<---1------|multicast listen |<---1--|
                                         |____| |_______________|


we need to discuss:
1. should we support beat heart?
every kimchi host will send periodic notify to tell others himself 
information?


2. should we support a "quit" message?
"quit" message tell other peers, that this kimchi quit normally. others 
can remove this from peers list.
But the kimchi can not send "quit" when aborting abnormally.

3. Do we store the local peers information in DB?
we can collection the local peers and send them immediately when user 
need to discover the peers.

We will extend to support remote peers, these information need to be 
stored in DB.

-- 
Thanks and best regards!

Sheldon Feng(???)<shaohef at linux.vnet.ibm.com>
IBM Linux Technology Center

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