Features/COLO
Feature Name
COarse-grained LOck-stepping Virtual Machines for Non-stop Service
Background
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 2015,KVM forum2016
Feature authors
- Name: Hailiang Zhang, Congyang Wen, Chen Zhang
- Email: zhang.zhanghailiang@huawei.com, wency@cn.fujitsu.com, zhangchen.fnst@fujitsu.com
Architecture
The architecture of COLO is shown in the bellow diagram. It consists of a pair of networked physical nodes: The primary node running the PVM, and the secondary node running the SVM to maintain a valid replica of the PVM. PVM and SVM execute in parallel and generate output of response packets for client requests according to the application semantics.
The incoming packets from the client or external network are received by the primary node, and then forwarded to the secondary node, so that Both the PVM and the SVM are stimulated with the same requests.
COLO receives the outbound packets from both the PVM and SVM and compares them before allowing the output to be sent to clients.
The SVM is qualified as a valid replica of the PVM, as long as it generates identical responses to all client requests. Once the differences in the outputs are detected between the PVM and SVM, COLO withholds transmission of the outbound packets until it has successfully synchronized the PVM state to the SVM.
Primary Node Secondary Node
+------------+ +-----------------------+ +------------------------+ +------------+
| | | HeartBeat |<----->| HeartBeat | | |
| Primary VM | +-----------|-----------+ +-----------|------------+ |Secondary VM|
| | | | | |
| | +-----------|-----------+ +-----------|------------+ | |
| | |QEMU +---v----+ | |QEMU +----v---+ | | |
| | | |Failover| | | |Failover| | | |
| | | +--------+ | | +--------+ | | |
| | | +---------------+ | | +---------------+ | | |
| | | | VM Checkpoint |-------------->| VM Checkpoint | | | |
| | | +---------------+ | | +---------------+ | | |
| | | | | | | |
|Requests<---------------------------^------------------------------------------>Requests|
|Responses----------------------\ /--|--------------\ /------------------------Responses|
| | | | | | | | | | | | |
| | | +-----------+ | | | | | | | +------------+ | | |
| | | | COLO disk | | | | | | | | | COLO disk | | | |
| | | | Manager |-|-|--|--------------|--|->| Manager | | | |
| | | +|----------+ | | | | | | | +-----------|+ | | |
| | | | | | | | | | | | | | |
+------------+ +--|------------|-|--|--+ +---|--|--------------|--+ +------------+
| | | | | | |
+-------------+ | +----------v-v--|--+ +---|--v-----------+ | +-------------+
| VM Monitor | | | COLO Proxy | | COLO Proxy | | | VM Monitor |
| | | |(compare packet) | | (adjust sequence)| | | |
+-------------+ | +----------|----^--+ +------------------+ | +-------------+
| | | |
+------------------|------------|----|--+ +---------------------|------------------+
| Kernel | | | | | Kernel | |
+------------------|------------|----|--+ +---------------------|------------------+
| | | |
+--------------v+ +--------v----|--+ +------------------+ +v-------------+
| Storage | |External Network| | External Network | | Storage |
+---------------+ +----------------+ +------------------+ +--------------+
Components
- COLO Block Replication (Please refer to BlockReplication)
- 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 context of primary VM 's image.
- COLO framework: COLO Checkpoint/Failover Controller
- Modifications of save/restore flow to realize continuous migration, to make sure the state of VM in Secondary side
- always be consistent with VM in Primary side.
- COLO Proxy:
- Delivers packets to Primary and Seconday, and then compare the reponse from both side. Then decide whether to
- start a checkpoint according to some rules.
Current Status
* Copyright (c) 2016 HUAWEI TECHNOLOGIES CO.,LTD. * Copyright (c) 2016 FUJITSU LIMITED * Copyright (c) 2016 Intel Corporation
Github:(Checkout to latest colo branch)
Failover command
We provide a qmp command:
x-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 communicate with COLO. Users can choose whatever heartbeat implementation they want.
Failover rule:
TODO:
How to setup/test COLO
Hardware requirements
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. you should have directly connected nic for each guest nic. If you don't have enouth directly connected nic, you can use vlan.
Network link topology
=================================normal ======================================
+--------+
|client |
master +----+---+ slave
-------------------------+ | + -------------------------+
PVM | + | |
+-------+ +----[eth0]-----[switch]-----[eth0]---------+ |
|guest | +---+-+ | | +---+-+ |
| [tap0]--+ br0 | | | | br0 | |
| | +-----+ [eth1]-----[forward]----[eth1]--+ +-----+ SVM |
+-------+ | | | +-------+|
| | | +-----+ | guest ||
[eth2]---[checkpoint]---[eth2] +--+br1 |-[tap0] ||
| | +-----+ | ||
| | +-------+|
-------------------------+ +--------------------------+
e.g.
master:
br0: 192.168.0.33
eth1: 192.168.1.33
eth2: 192.168.2.33
slave:
br0: 192.168.0.88
br1: no ip address
eth1: 192.168.1.88
eth2: 192.168.2.88
NOTE: br0 is setup by adminitrator but br1 is setup by colo now.
===========================after failover=====================================
+--------+
|client |
master (dead) +----+---+ slave (alive)
-------------------------+ | ---------------------------+
PVM | + | |
+-------+ +----[eth0]-----[switch]-----[eth0]-------+ |
|guest | +---+-+ | | +---+-+ |
| [tap0]--+ br0 | | | | br0 +--+ |
| | +-----+ [eth1]-----[forward]----[eth1] +-----+ | SVM |
+-------+ | | | +-------+|
| | +-----+ | | guest ||
[eth2]---[checkpoint]---[eth2] |br1 | +[tap0] ||
| | +-----+ | ||
| | +-------+|
-------------------------+ +--------------------------+
Test environment prepare
- Prepare host kernel
- colo-proxy kernel module need cooperate with linux kernel.
- You should patch colo-patch-for-kernel.patch into kernel codes,
- then compile kernel and intall the new kernel (Recommend kernel-3.18.10)
- Proxy module
- proxy module is used for network packets compare.
# git clone https://github.com/coloft/colo-proxy.git # cd ./colo-proxy # make # make install
- Modified iptables
- We have add a new rule to iptables command.
# git clone https://github.com/coloft/iptables.git # cd ./iptables # git checkout colo # ./autogen.sh && ./configure # make && make install
- Modified arptables
- Please get the latest arptables and then compile and install
- Qemu colo
- Checkout the latest colo branch from colo-v1.5-basic or
# cd qemu # ./configure --target-list=x86_64-softmmu --enable-colo # make
- Set Up the Bridge and network environment
- You must setup you network environment like above picture(Network link topology Normal).
In master, setup a bridge br0, using command brctl, like: # ifconfig eth0 down # ifconfig eth0 0.0.0.0 # brctl addbr br0 # brctl addif br0 eth0 # ifconfig br0 192.168.0.33 netmask 255.255.255.0 # ifconfig eth0 up In slave, setup br0 like master side
- Qemu-ifup/Qemu-ifdown
- We need a script to bring up the TAP interface.
- a qemu-ifdown script is needed to reset you networking configuration which is configured by qemu-ifup script
- You can find this info from http://en.wikibooks.org/wiki/QEMU/Networking.
NOTE: Don't forget to change this script file permission to be executable
Master:
root@master# cat /etc/qemu-ifup
#!/bin/sh
switch=br0
if [ -n "$1" ]; then
ip link set $1 up
brctl addif ${switch} $1
fi
root@master# cat /etc/qemu-ifdown
!/bin/sh
switch=br0
if [ -n "$1" ]; then
brctl delif ${switch} $1
fi
Slave:
like Master side
Test steps
(Note: We apply two scripts to help completing step (1) ~ step (2), primary-colo.sh secondary-colo.sh)
- (1) Load modeule
# modprobe xt_PMYCOLO (For slave side, modprobe xt_SECCOLO) # modprobe nf_conntrack_colo (Other colo module will be automatically loaded by script colo-proxy-script.sh) # modprobe xt_mark # modprobe kvm-intel
- (2) Startup qemu
- Master side:
# x86_64-softmmu/qemu-system-x86_64 -machine pc-i440fx-2.3,accel=kvm,usb=off \ -netdev tap,id=hn0,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown,\ colo_script=./scripts/colo-proxy-script.sh,forward_nic=eth1 -device virtio-net-pci,id=net-pci0,netdev=hn0 \ -boot c -drive if=virtio,id=disk1,driver=quorum,read-pattern=fifo,cache=none,aio=native,\ children.0.file.filename=/mnt/sdb/pure_IMG/redhat/redhat-7.0.img,children.0.driver=raw \ -vnc :7 -m 2048 -smp 2 -device piix3-usb-uhci -device usb-tablet -monitor stdio -S
- Slave side:
# qemu-img create -f qcow2 /mnt/ramfs/active_disk.img 10G # qemu-img create -f qcow2 /mnt/ramfs/hidden_disk.img 10G # x86_64-softmmu/qemu-system-x86_64 -machine pc-i440fx-2.3,accel=kvm,usb=off \ -netdev tap,id=hn0,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown,\ colo_script=./scripts/colo-proxy-script.sh,forward_nic=eth1 -device virtio-net-pci,id=net-pci0,netdev=hn0 \ -drive if=none,driver=raw,file=/mnt/sdb/pure_IMG/redhat/redhat-7.0.img,id=colo1,cache=none,aio=native \ -drive if=virtio,driver=replication,mode=secondary,throttling.bps-total-max=70000000,\ file.file.filename=/mnt/ramfs/active_disk.img,file.driver=qcow2,\ file.backing.file.filename=/mnt/ramfs/hidden_disk.img,\ file.backing.driver=qcow2,\ file.backing.backing.backing_reference=colo1,\ file.backing.allow-write-backing-file=on \ -vnc :7 -m 2048 -smp 2 -device piix3-usb-uhci -device usb-tablet -monitor stdio -incoming tcp:0:8888
Note: 1. The export name in secondary QEMU command line is the secondary disk's id. In the expampe, it is colo1. 2. The export name for primary disk is not in the command line. It is in child_add's argument. Please see below. 3. The export name for the same disk must be the same 4. The qmp command nbd-server-start and nbd-server-add must be run before running the qmp command migrate on primary QEMU 5. Don't use nbd-server-start's other options 6. Active disk, hidden disk and nbd target's length should be the same. 7. It is better to put active disk and hidden disk in ramdisk. 8. It is all a single argument to -drive, and you should ignore the leading whitespace.
- (3) On Secondary VM's QEMU monitor, issue command (This command must be run before command in step (4))
(qemu) nbd_server_start 192.168.2.88:8889 (qemu) nbd_server_add -w colo1
- (4) On Primary VM's QEMU monitor, issue command:
(qemu) child_add disk1 child.driver=replication,child.mode=primary,child.file.host=192.168.2.88,child.file.port=8889,child.file.export=colo1,child.file.driver=nbd,child.ignore-errors=on (qemu) migrate_set_capability colo on (qemu) migrate tcp:192.168.2.88:8888
Note: 1. There should be only one NBD Client. 2. host is the secondary physical machine's hostname or IP 3. Each disk must have its own export name.
- (5) Done
- You will see two runing VMs, whenever you make changes to PVM, SVM will be synced.
- (6) 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>