1. Code Migration Russell T. Potee, III

2. Overview Why Code Migration? Code Migration Models Migration and Handling Resources Heterogeneous Systems Migration Security

3. Why Code Migration? Process Migration - definition  Transfer an entire running process from one machine to another Load distribution Measured by CPU queue length or utilization Good for computational systems Reduce Network Bandwidth  Migrate part of client application to server Migrate part of client application to database server to perform many database operations Send only result across network

4. Why Code Migration? Reduce Network Bandwidth  Migrate part of server application to client Migrate part of database server to client to process forms on client side Reduces database operations over the network XSS - Javascript Parallelism  Mobile Agent Dynamic Configuration of Distributed Systems  Download and Initialize Code

5. Code Migration Framework  Code Segment Set of instructions being executed  Resource Segment References to external resources Files, printers, devices, et cetera  Execution Segment Process state Private data Stack Instruction pointer Code Migration Models

6. Weak Mobility  Transfer code segment and initialized data  Portable code  Predefined starting positions Java Applets Strong Mobility  Transfer includes execution segment  Process can be stopped, moved to another machine, and resumed

7. Code Migration Models Sender-initiated  Code transfer is initiated by machine currently executing the code  Example Uploading programs to a computational server Receiver-initiated  Transfer is initiated by machine that will execute code  Example Java applets

8. Handling Resources Process-to-resource binding  Binding by identifier (strong)‏ Process refers to resources by their identifiers Example  URL  Binding by value (weaker)‏ Process refers to another resource with the same value  Binding by type (weakest)‏ Process refers to local devices

9. Handling Resources Resource-to-machine binding  Unattached resources Can be moved easily  Data Files  Fastened resources Can be moved at high cost  Database  Fixed resources Cannot be moved  Local devices

10. Heterogeneous Systems Heterogeneous systems are platforms with different operating systems and/or different machine architectures Problems with heterogeneous systems is similar to those of portability Solutions  Highly portable languages Scripting languages, interpreted languages (Java)‏  Migrating computing environments  Migrating virtual machines

11. Migration Security Protecting mobile agents  need to protect sensitive data Three mechanisms for securing mobile agents  Read-only state Data items are signed by agent's owner  Append-only state Data can only be appended to logs  Selective reading Each data entry can only be updated by selected servers

12. Migration Security Protecting hosts against malicious mobile code  Sandbox Monitor specific instructions, registers, memory regions Easier to do with interpreted languages  Java sandbox  Playground Separate machines exist to execute mobile code  Code-signing  Stack introspection  Name space management

13. Sources Tanenbaum, A., Van Steen, M.: Distributed Systems: Principles and Paradigms, Upper Saddle River, NJ: Prentice Hall, 2007 Fuggetta, A., Picco, G.P., and Vigna, G: “Understanding Code Mobility.” IEEE Trans. Soft. Eng., May 1998. Milojicic, D., Douglis, F., Paindeveine, Y., Wheeler, R., Zhou, S.: “Process Migration.” ACM Computing Surv., Sept 2000.

14. Sources Clark, C., Fraser K., Hand, S., Hansen, J.G., Jul, E., Limpoch, C., Pratt, I., Warfield, A.: “Live Migration of Virtual Machines.” Proc. Second Symp. Network Systems and Design Impl., (Boston, MA). Berkley, CA: USENIX, 2005.