Features/COLO

From QEMU

Summary

COLO-COarse Grain LOck Stepping
Paper: academia paper in SOCC 2013

Virtual machine (VM) replication is a well known technique for providing application-agnostic software-implemented hardware fault tolerance "non-stop service". COLO 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 response 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. The idea is presented in Xen summit 2012, and 2013, and academia paper in SOCC 2013. It's also presented in KVM forum 2013: Kvm-forum-2013-COLO.pdf

There's also several RFC proposal posted to QEMU devel maillist:

http://lists.nongnu.org/archive/html/qemu-devel/2014-06/msg05567.html
http://lists.nongnu.org/archive/html/qemu-devel/2014-09/msg04459.html

Wiki: http://wiki.qemu.org/Features/COLO
Github:

https://github.com/coloft/qemuCheckout to latest colo branch
https://github.com/macrosheep/qemu
https://github.com/gao-feng/colo-proxy.git
* Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD.
* Copyright (c) 2015 FUJITSU LIMITED
* Copyright (c) 2015 Intel Corporation

Components

  • COLO Manager:
    • COLO Controller - Modifications of save/restore flow (Refer to MacroCheckpointing).
    • COLO Disk Manager - When primary VM writes data into image, the colo disk manger captures this data
and send it to secondary VM’s which makes sure the context of secondary VM's image is consentient with
the ontext of primary VM 's image.
  • COLO Proxy
We need an module to compare the packets returned by Primary VM and Secondary VM
and decide whether to start a checkpoint according to some rules. It is a linux kernel module
for host.

Current Status

  • COLO Manager:
    • COLO Controller/Frame (View on Github Checkout to latest colo branch, RFC patch has been posted(v3))
    • COLO Disk Manager (RFC patch has been posted)
  • COLO Proxy(View on Github)

Failover & Heartbeat

We provide a qmp command: 

colo_lost_heartbeat

This command will tell COLO that heartbeat is lost. COLO will do some action accordingly.

External heartbeat modules can use this qmp command to communicatewith COLO. Users can choose whatever heartbeat implementation they want.

Failover rule:
TODO

Block replication

This is the COLO Disk Manager implementation. Please refer to http://wiki.qemu.org/Features/BlockReplication

Installation

  • Hardware requriements

There is at least one directly connected nic to forward the network requests from client to secondary vm. The directly connected nic must not be used by any other purpose. If your guest has more than one nic, you should have directly connected nic for each guest nic. If you don't have enouth directly connected nic, you can use vlan.

  • Checkout the latest colo branch on Github.
/*for example, the latest brach is colo_v0.99, the version may rapidly grows, please make sure you are using the latest branch*/
# git clone https://github.com/macrosheep/qemu
# git checkout colo_v0.99
  • configure and make:
# ./configure --target-list=x86_64-softmmu --enable-colo
# make
  • Install COLO agent module:
    • Download COLO agent, and compile it, it is the kernel module, so copy the module to the directory /lib/modules/<version>/updates/, and run depmod.
# git clone https://github.com/wencongyang/colo-agent
# cd colo-agent; make
# cp *.ko /lib/modules/<version>/updates/
# depmod

Test environment prepare:

  • Prepare host kernel
colo-proxy kernel module need cooperate with linux kernel.
You should put a kernel patch 'colo-patch-for-kernel.patch'
(It's based on linux kernel-3.19) which you can get from
https://github.com/gao-feng/colo-proxy.git
and then compile kernel and intall the new kernel.
  • Proxy module
    • proxy module is used for network packets compare.
# git clone https://github.com/gao-feng/colo-proxy.git
# cd ./colo-proxy
# make
# make install

# cd qemu
# ./configure --target-list=x86_64-softmmu --enable-colo --enable-quorum
# make

Test steps:

  • load modeule
# modprobe nf_conntrack_colo
  • startup qemu
    • master:
# qemu-system-x86_64 -enable-kvm -netdev tap,id=hn0,colo_script=./scripts/colo-proxy-script.sh,colo_nicname=eth1 \
-device virtio-net-pci,id=net-pci0,netdev=hn0 -boot c -drive driver=quorum,read-pattern=first,children.0.file.filename=suse11_3.img,children.0.driver=raw,children.1.file.driver=nbd+colo,children.1.file.host=192.168.2.88,children.1.file.port=8889,children.1.file.export=colo1,children.1.driver=raw,if=virtio 
-vnc :7 -m 2048 -smp 2 -device piix3-usb-uhci -device usb-tablet -monitor stdio -S
    • slave:
# qemu-system-x86_64 -enable-kvm -netdev tap,id=hn0,colo_script=./scripts/colo-proxy-script.sh,colo_nicname=eth1 
-device virtio-net-pci,id=net-pci0,netdev=hn0 -boot c -drive driver=blkcolo,export=colo1,backing.file.filename=suse11_3.img,backing.driver=raw,if=virtio 
-vnc :7 -m 2048 -smp 2 -device piix3-usb-uhci -device usb-tablet -monitor stdio -incoming tcp:0:8888
  • On Secondary VM's QEMU monitor, run
(qemu) nbd_server_start 192.168.2.88:8889
  • on Primary VM's QEMU monitor, run following command:
(qemu) migrate_set_capability colo on
(qemu) migrate tcp:192.168.2.88:8888
  • done
    • You will see two runing VMs, whenever you make changes to PVM, SVM

will be synced to PVM's state.

  • failover test:
    • You can kill SVM (PVM) and run 'colo_lost_heartbeat' in PVM's (SVM's) monitor

at the same time, then PVM (SVM) will failover and client will not feel this change.

  • For Questions/Issues, please contact: Zhang Hailiang <zhang.zhanghailiang@huawei.com>;Yang Hongyang <yanghy@cn.fujitsu.com>; Wen Congyang <wency@cn.fujitsu.com>

Links

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