Re: [Qemu-devel] [RFC PATCH v2 00/10] Add colo-proxy based on netfilter

[Zhang Chen <zhangchen.fnst@cn.fujitsu.com>]

> Sure.
>
> Two main comments/suggestions:
>
> - TCP analysis is missed in current version, maybe you point a git tree
> (or another version of RFC) to me for a better understanding of the
> design. (Just a skeleton for TCP should be sufficient to discuss).
> - I prefer to make the code as reusable as possible. So it's better to
> split/decouple the reusable parts from the codes. So a vague idea is:
>
> 1) Decouple the packet comparing from the netfilter. You've achieved
> this 99% since the work has been done in a thread. Just let the thread
> poll sockets directly, then the comparing have the possibility to be
> reused by other kinds of dataplane.
> 2) Implement traffic mirror/redirector as filter.
> 3) Implement TCP seq rewriting as a filter.
>
> Then, in primary node, you need just a traffic mirror, which did:
> - mirror ingress traffic to secondary node
> - mirror outgress traffic to packet comparing thread
>
> And in secondadry node, you need two filters:
> - A TCP seq rewriter which adjust tcp sequence number.
> - A traffic redirector which redirect packet from a socket as ingress
> traffic, and redirect outgress traffic to the socket which could be
> polled by remote packet comparing thread.
>   
> Thoughts?
>
> Thanks
>
>> Thanks
>> zhangchen
>


Hi, Jason.
We consider your suggestion to split/decouple
the reusable parts from the codes.
Due to filter plugin are traversed one by one in order
we will split colo-proxy to three filters in each side.

But in this plan,primary and secondary both have socket
server,startup is a problem.


  Primary qemu                                                       Secondary qemu
+----------------------------------------------------------+       +-----------------------------------------------------------+
| +-----------------------------------------------------+  |       |  +------------------------------------------------------+ |
| |                                                     |  |       |  |                                                      | |
| |                        guest                        |  |       |  |                        guest                         | |
| |                                                     |  |       |  |                                                      | |
| +-----------^--------------+--------------------------+  |       |  +---------------------+--------+-----------------------+ |
|             |              |                             |       |                        ^        |                         |
|             |              |                             |       |                        |        |                         |
|             +-------------------------------------------------+  |                        |        |                         |
|  netfilter  |              |                             |    |  |   netfilter            |        |                         |
| +-----------------------------------------------------+  |    |  |  +------------------------------------------------------+ |
| |           |              |     filter excute order  |  |    |  |  |                     |        |  filter excute order  | |
| |           |              |    +-------------------> |  |    |  |  |                     |        | +-------------------> | |
| |           |              |                          |  |    |  |  |                     |        |   TCP                 | |
| | +---------+-+     +------v-----+    +----+ +-----+  |  |    |  |  | +-----------+   +---+----+---v+rewriter+  +--------+ | |
| | |           |     |            |    |            |  |  |    |  |  | |           |   |        |             |  |        | | |
| | |  mirror   |     |  redirect  +---->  compare   |  |  |    +--------> mirror   +---> adjust |   adjust    +-->redirect| | |
| | |  client   |     |  server    |    |            |  |  |       |  | |  server   |   | ack    |   seq       |  |client  | | |
| | |           |     |            |    |            |  |  |       |  | |           |   |        |             |  |        | | |
| | +----^------+     +----^-------+    +-----+------+  |  |       |  | +-----------+   +--------+-------------+  +----+---+ | |
| |      |     tx          |      rx          |     rx  |  |       |  |            tx                        all       |  rx | |
| +-----------------------------------------------------+  |       |  +------------------------------------------------------+ |
|        |                 +-------------------------------------------------------------------------------------------+       |
|        |                                    |            |       |                                                           |
+----------------------------------------------------------+       +-----------------------------------------------------------+
          |                                    |
          |guest receive                       |guest send
          |                                    |
+--------+------------------------------------v------------+
|                                                          |
|                                                          |
|                         tap                              |                              NOTE: filter direction is rx/tx/all
|                                                          |                              rx:receive packets sent to the netdev
|                                                          |                              tx:receive packets sent by the netdev
+----------------------------------------------------------+







guest recv packet route

primary
tap --> mirror client filter
mirror client will send packet to guest,at the
same time, copy and forward packet to secondary
mirror server.

secondary
mirror server filter --> TCP rewriter
if recv packet is TCP packet,we will adjust ack
and update TCP checksum, then send to secondary
guest. else directly send to guest.


guest send packet route

primary
guest --> redirect server filter
redirect server filter recv primary guest packet
but do nothing, just pass to next filter.

redirect server filter --> compare filter
compare filter recv primary guest packet then
waiting scondary redirect packet to compare it.
if packet same,send primary packet and clear secondary
packet, else send primary packet and do
checkpoint.

secondary
guest --> TCP rewriter filter
if the packet is TCP packet,we will adjust seq
and update TCP checksum. then send it to
redirect client filter. else directly send to
redirect client filter.

redirect client filter --> redirect server filter
forward packet to primary


In failover scene（primary is down）, the TCP rewriter will keep servicing
for the TCP connection which is established after the last checkpoint。



How about this plan?


> .
>

-- 
Thanks
zhangchen