The ability to update software with critical bug fixes and security mitigations while minimizing downtime is extremely important to customers and cloud service providers. In this blog post, we present QEMU Live Update, a new method for updating a running QEMU instance to a new version while minimizing the impact to the VM guest. The guest pauses briefly, for less than 100 milliseconds in our prototype, without loss of internal state or external connections. Live Update uses resources more efficiently than Live Migration. The latter ties up the source and target hosts, and consumes more memory and network bandwidth, and does so for an indeterminate period of time that depends on when the copy phase converges. Live migration is prohibitively expensive if large local storage must be copied across the network to the target.
The ability to update software with critical bug fixes and security mitigations while minimizing downtime is important to customers.