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Re: [Qemu-devel] [POC]colo-proxy in qemu


From: Zhang Chen
Subject: Re: [Qemu-devel] [POC]colo-proxy in qemu
Date: Wed, 11 Nov 2015 10:46:12 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0



On 11/10/2015 06:54 PM, Dr. David Alan Gilbert wrote:
* Tkid (address@hidden) wrote:
Hi,all

We are planning to reimplement colo proxy in userspace (Here is in qemu) to
cache and compare net packets.This module is one of the important components
of COLO project and now it is still in early stage, so any comments and
feedback are warmly welcomed,thanks in advance.

## Background
COLO FT/HA (COarse-grain LOck-stepping Virtual Machines for Non-stop
Service)
project is a high availability solution. Both Primary VM (PVM) and Secondary
VM
(SVM) run in parallel. They receive the same request from client, and
generate
responses in parallel too. If the response packets from PVM and SVM are
identical, they are released immediately. Otherwise, a VM checkpoint (on
demand)
is conducted.
Paper:
http://www.socc2013.org/home/program/a3-dong.pdf?attredirects=0
COLO on Xen:
http://wiki.xen.org/wiki/COLO_-_Coarse_Grain_Lock_Stepping
COLO on Qemu/KVM:
http://wiki.qemu.org/Features/COLO

By the needs of capturing response packets from PVM and SVM and finding out
whether they are identical, we introduce a new module to qemu networking
called
colo-proxy.

This document describes the design of the colo-proxy module

## Glossary
   PVM - Primary VM, which provides services to clients.
   SVM - Secondary VM, a hot standby and replication of PVM.
   PN - Primary Node, the host which PVM runs on
   SN - Secondary Node, the host which SVM runs on

## Our Idea ##

COLO-Proxy
COLO-Proxy is a part of COLO,based on qemu net filter and it's a plugin for
qemu net filter.the function keep SVM connect normal to PVM and compare
PVM's packets to SVM's packets.if difference,notify COLO do checkpoint.

== Workflow ==


+--+                                      +--+
|PN|                                      |SN|
+-----------------------+                 +-----------------------+
| +-------------------+ |                 | +-------------------+ |
| |                   | |                 | |                   | |
| |        PVM        | |                 | |        SVM        | |
| |                   | |                 | |                   | |
| +--+-^--------------+ |                 | +-------------^----++ |
|    | |                |                 |               |    |  |
|    | | +------------+ |                 | +-----------+ |    |  |
|    | | |    COLO    | |    (socket)     | |    COLO   | |    |  |
|    | | | CheckPoint +---------------------> CheckPoint| |    |  |
|    | | |            | |      (6)        | |           | |    |  |
|    | | +-----^------+ |                 | +-----------+ |    |  |
|    | |   (5) |        |                 |               |    |  |
|    | |       |        |                 |               |    |  |
| +--v-+--------------+ | Forward(socket) | +-------------+----v+ |
| |COLO Proxy  |      +-------+(1)+--------->seq&ack adjust(2)| | |
| |      +-----+------+ |                 | +-----------------+ | |
| |      | Compare(4) <-------+(3)+---------+     COLO Proxy    | |
| +-------------------+ | Forward(socket) | +-------------------+ |
++Qemu+-----------------+                 ++Qemu+-----------------+
            | ^
            | |
            | |
   +--------v-+--------+
   |                   |
   |      Client       |
   |                   |
   +-------------------+


(1)When PN receive client packets,PN COLO-Proxy copy and forward packets to
SN COLO-Proxy.
(2)SN COLO-Proxy record PVM's packet inital seq & adjust client's ack,send
adjusted packets to SVM
(3)SN Qemu COLO-Proxy recieve SVM's packets and forward to PN Qemu
COLO-Proxy.
What protocol are you using for the data carried over the Forward(socket)?
I'm just wondering if there's an existing layer2 tunneling protocol that
it would be best to use.
Currently,we will use raw tcp socket send a packet's length then send the packet.
(4)PN Qemu COLO-Proxy enqueue SVM's packets and enqueue PVM's packets,then
compare PVM's packets data with SVM's packets data. If packets is different,
compare
module notify COLO CheckPoint module to do a checkpoint then send PVM's
packets to
client and drop SVM's packets, otherwise, just send PVM's packets to client
and
drop SVM's packets.
(5)notify COLO-Checkpoint module checkpoint is needed
(6)Do COLO-Checkpoint

### QEMU space TCP/IP stack(Based on SLIRP) ###
We need a QEMU space TCP/IP stack to help us to analysis packet. After
looking
into QEMU, we found that SLIRP

http://wiki.qemu.org/Documentation/Networking#User_Networking_.28SLIRP.29

is a good choice for us. SLIRP proivdes a full TCP/IP stack within QEMU, it
can
help use to handle the packet written to/read from backend(tap) device which
is
just like a link layer(L2) packet.
I still think SLIRP might be painful; but it might be an easy one to start
with.

### Packet enqueue and compare ###
Together with QEMU space TCP/IP stack, we enqueue all packets sent by PVM
and
SVM on Primary QEMU, and then compare the packet payload for each
connection.
Dave

--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
.





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