[RFC] COLO HA Project proposal

Hongyang Yang
2014-06-24T02:08:00Z

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Background:
COLO HA 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 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:
http://www.linux-kvm.org/wiki/images/1/1d/Kvm-forum-2013-COLO.pdf
Please refer to above document for detailed information.

The attached was the architecture of kvm-COLO we proposed.
- COLO Manager: Requires modifications of qemu
- COLO Controller
COLO Controller includes modifications of save/restore
flow just like MC(macrocheckpoint), a memory cache on
secondary VM which cache the dirty pages of primary VM
and a failover module which provides APIs to communicate
with external heartbead module.
- COLO Disk Manager
When pvm writes data into image, the colo disk manger
captures this data and send it to the colo disk manger
which makes sure the context of svm's image is consentient
with the context of pvm's image.

- COLO Agent("Proxy module" in the arch picture)
We need an agent 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.

- Other minor modifications
We may need other modifications for better performance.

--
Thanks,
Yang.

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