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

2. 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.

3. 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.

4. 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)

5. 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

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

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

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

9. 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

10. Questions