Process Migration Troy Cogburn and Gilbert Podell-Blume CS455: Introduction to Distributed Systems Computer Science Department, Colorado State University

Why is this problem important? Process migration helps provide: fault tolerance load balancing transparency Part of the backend of services like AWS EC2 helps further abstract VM from underlying hardware Allows processes to move systems to take advantage of data locality or better processing power.

Problem characterization Requirements to migrate a running process while minimizing do: Origin node issues migration request to remote node. Origin node suspends migrating process and redirects incoming messages to queue Origin node records process state information: register contents memory open files and ports other info (OS dependent) Process state information is transmitted to destination node Hard migration: full process image Soft migration: copy minimal state info to a new process System forwards messages to new instance, including aforementioned queue Process resumes on destination note. May continue fetching state information from origin, depending on migration method.

Trade-off space, solution constraints Performance trade-offs: Pre-copy: transmit memory before CPU state may retransmit dirtied pages several times potentially high network overhead Post-copy transmit memory after CPU state transmit memory in response to page faults on new process potential performance hit from network I/O Solution constraints OS support requirements; (more support better performance; less support easier implementation) Transparency (obscure migration effects from other tasks)

Dominant approaches Sprite Early Distributed Operating System Individual Kernels working closely together through RPC Mach Early example of microkernel Mach Tasks Distributed Memory Management Process Replication Active vs Passive Increased redundancy = Increased Reliability

Dominant approaches (cont.) Virtualization VMware(VSphere) Full Machine Virtualization Containerization Software Containers(Docker) Distributed lightweight OS (CoreOS)

Insights Gleaned Virtualization Abstraction of machines “Live” or “Hot” Migration Containers with abstracted OS

Future Possibilities in Migration Virtualization and Migration over WAN Mobile Workspaces Decentralized Cloud …IF bandwidth keeps increasing.

Future Trade-offs & Constraints More WAN Migration → More Security Risk (as with any sensitive network communications) More migration in heterogeneous environments → more obvious capability or compatibility gaps between processes and hosts

Questions