Checkpoint-restart for a network of virtual machines

The ability to easily deploy parallel computations on the Cloud is becoming ever more important. The first uniform mechanism for checkpointing a network of virtual machines is described. This is important for the parallel versions of common productivity software. Potential examples of parallelism include Simulink for MATLAB, parallel R for the R statistical modelling language, parallel blast.py for the BLAST bioinformatics software, IPython.parallel for Python, and GNU parallel for parallel shells. The checkpoint mechanism is implemented as a plugin in the DMTCP checkpoint-restart package. It operates on KVM/QEMU, and has also been adapted to Lguest and pure user-space QEMU. The plugin is surprisingly compact, comprising just 400 lines of code to checkpoint a single virtual machine, and 200 lines of code for a plugin to support saving and restoring network state. Incremental checkpoints of the associated virtual filesystem are accommodated through the Btrfs filesystem. Experiments demonstrate checkpoint times of a fraction of a second by using forked checkpointing, mmap-based restart, and incremental Btrfs-based snapshots.