COLO-proxy ---------- Copyright (c) 2016 Intel Corporation Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD. Copyright (c) 2016 Fujitsu, Corp. This work is licensed under the terms of the GNU GPL, version 2 or later. See the COPYING file in the top-level directory. This document gives an overview of COLO proxy's design. == Background == COLO-proxy is a part of COLO project. It is used to compare the network package to help COLO decide whether to do checkpoint. With COLO-proxy's help, COLO greatly improves the performance. The filter-redirector, filter-mirror, colo-compare and filter-rewriter compose the COLO-proxy. == Architecture == COLO-Proxy is based on qemu netfilter and it's a plugin for qemu netfilter (except colo-compare). It keep Secondary VM connect normally to client and compare packets sent by PVM with sent by SVM. If the packet difference, notify COLO-frame to do checkpoint and send all primary packet has queued. Otherwise just send the queued primary packet and drop the queued secondary packet. Below is a COLO proxy ascii figure: Primary qemu Secondary qemu +--------------------------------------------------------------+ +----------------------------------------------------------------+ | +----------------------------------------------------------+ | | +-----------------------------------------------------------+ | | | | | | | | | | | guest | | | | guest | | | | | | | | | | | +-------^--------------------------+-----------------------+ | | +---------------------+--------+----------------------------+ | | | | | | ^ | | | | | | | | | | | | +------------------------------------------------------+ | | | | |netfilter| | | | | | netfilter | | | | +----------+ +----------------------------+ | | | +-----------------------------------------------------------+ | | | | | | | out | | | | | | filter excute order | | | | | | +-----------------------------+ | | | | | | +-------------------> | | | | | | | | | | | | | | | | TCP | | | | +-----+--+-+ +-----v----+ +-----v----+ |pri +----+----+sec| | | | +------------+ +---+----+---v+rewriter++ +------------+ | | | | | | | | | | |in | |in | | | | | | | | | | | | | | | | filter | | filter | | filter +------> colo <------+ +--------> filter +--> adjust | adjust +--> filter | | | | | | mirror | |redirector| |redirector| | | compare | | | | | | redirector | | ack | seq | | redirector | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +----^-----+ +----+-----+ +----------+ | +---------+ | | | | +------------+ +--------+--------------+ +---+--------+ | | | | | tx | rx rx | | | | | tx all | rx | | | | | | | | | | +-----------------------------------------------------------+ | | | | +--------------+ | | | | | | | | | filter excute order | | | | | | | | | | +----------------> | | | +--------------------------------------------------------+ | | +-----------------------------------------+ | | | | | | | | | +--------------------------------------------------------------+ +----------------------------------------------------------------+ |guest receive | guest send | | +--------+----------------------------v------------------------+ | | NOTE: filter direction is rx/tx/all | tap | rx:receive packets sent to the netdev | | tx:receive packets sent by the netdev +--------------------------------------------------------------+ 1.Guest receive 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 receive packet is TCP packet,we will adjust ack and update TCP checksum, then send to secondary guest. Otherwise directly send to guest. 2.Guest send packet route: Primary: Guest --> Redirect Server Filter Redirect server filter receive primary guest packet but do nothing, just pass to next filter. Redirect Server Filter --> COLO-Compare COLO-compare receive primary guest packet then waiting scondary redirect packet to compare it. If packet same,send queued primary packet and clear queued secondary packet, Otherwise send primary packet and do checkpoint. COLO-Compare --> Another Redirector Filter The redirector get packet from colo-compare by use chardev socket. Redirector Filter --> Tap Send the packet. 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. Otherwise directly send to redirect client filter. Redirect Client Filter --> Redirect Server Filter Forward packet to primary. == Components introduction == Filter-mirror is a netfilter plugin. It gives qemu the ability to mirror packets to a chardev. Filter-redirector is a netfilter plugin. It gives qemu the ability to redirect net packet. Redirector can redirect filter's net packet to outdev, and redirect indev's packet to filter. filter + redirector | +--------------+ | | | | | | | | | indev +---------+ +----------> outdev | | | | | | | | | +--------------+ | v filter COLO-compare, we do packet comparing job. Packets coming from the primary char indev will be sent to outdev. Packets coming from the secondary char dev will be dropped after comparing. COLO-comapre need two input chardev and one output chardev: primary_in=chardev1-id (source: primary send packet) secondary_in=chardev2-id (source: secondary send packet) outdev=chardev3-id Filter-rewriter will rewrite some of secondary packet to make secondary guest's tcp connection established successfully. In this module we will rewrite tcp packet's ack to the secondary from primary,and rewrite tcp packet's seq to the primary from secondary. == Usage == Here is an example using demonstration IP and port addresses to more clearly describe the usage. Primary(ip:3.3.3.3): -netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown -device e1000,id=e0,netdev=hn0,mac=52:a4:00:12:78:66 -chardev socket,id=mirror0,host=3.3.3.3,port=9003,server,nowait -chardev socket,id=compare1,host=3.3.3.3,port=9004,server,nowait -chardev socket,id=compare0,host=3.3.3.3,port=9001,server,nowait -chardev socket,id=compare0-0,host=3.3.3.3,port=9001 -chardev socket,id=compare_out,host=3.3.3.3,port=9005,server,nowait -chardev socket,id=compare_out0,host=3.3.3.3,port=9005 -object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0 -object filter-redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out -object filter-redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0 -object colo-compare,id=comp0,primary_in=compare0-0,secondary_in=compare1,outdev=compare_out0 Secondary(ip:3.3.3.8): -netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,down script=/etc/qemu-ifdown -device e1000,netdev=hn0,mac=52:a4:00:12:78:66 -chardev socket,id=red0,host=3.3.3.3,port=9003 -chardev socket,id=red1,host=3.3.3.3,port=9004 -object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0 -object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1 Note: a.COLO-proxy must work with COLO-frame and Block-replication. b.Primary COLO must be started firstly, because COLO-proxy needs chardev socket server running before secondary started. c.Filter-rewriter only rewrite tcp packet.