1. Slingshot: Deploying Stateful Services in Wireless Hotspots Ya-Yunn Su Jason Flinn University of Michigan Presenter: Youngki, Lee

2. Outline Motivation Problem Design principles Implementation Evaluation Conclusion

3. Motivation Portability: take everywhere –Easy to carry and less obtrusive –Limited in resources Performance: run demanding applications –More processing power and storage capacity –Bulkier and heavier PerformancePortability Mobile Computer

4. AP Wireless Hotspot Internet Problem: Remote Execution VNC Server VNC client Limited bandwidth (T1 line, 1.5Mbps) High latency

5. AP Wireless Hotspot Internet Design Principles (1) : Location, location, location Surrogate Home Server VNC client VM VNC

6. AP Wireless Hotspot Internet Design Principles(2) : Replicate rather than migrate Surrogate Home Server Problems: 1.No service during migration 2.Loss state on surrogate failure VNC client VM VNC

7. AP Wireless Hotspot Internet Surrogate Home Server VNC client Home replica always available No state loss on surrogate failure VM VNC VM VNC Design Principles(2) : Replicate rather than migrate First-class Replica Second-class Replica

8. Design Principles(3) : Ease of management Surrogates must be easy to manage if they are to be widely deployed. –They must require little to no supervision. –They should be appliances that require little configuration Slingshot –Minimizes the surrogate computing base –Uses a heavyweight virtual machine –Places no hard state on surrogates

9. Outline Motivation Problem Design principles Implementation Evaluation Conclusion

10. Slingshot Overview Local Component Client proxy Home Server Surrogate Slingshot applications - Remote desktop: VNC - Speech recognition: IBM ViaVoice Request Remote service Virtual Machine Service Database Remote service Virtual Machine Service Cache

11. The Home Server Service database –Stores the state of every service( 뒷장 ) under its purview in its service data. –Reduce the storage costs of virtual machine disk images using the content-addressable storage. Home server director –Initiation and termination of requested service –Ballooning technique to reduce the size of volatile sate( 위치 ) Remote service Virtual Machine Service Database Director

12. State of a Remote Service The virtual machine state contains: Volatile state: memory image and registers –Unique to each service –Compressed and stored as individual files Persistent state: virtual disk image –Large: ex. 4 GB for our VNC service –Stored in content addressable database

13. Content Addressable Database Disk Blocks SHA-1Ref countoffset ABC218 Chunk Database Chunk Table for VNC Hash Table Block #SHA-1 0ABC Chunk Table for Speech Recognition Block #SHA-1 5ABC This runs on the home server Built upon Internet Suspend Resume [ Kozuch02]

14. Surrogate Surrogate director –Accepts connections from any client that wishes to instantiate a second-class replica Access-control policies are required –Get volatile state and chunk table from the home server –Starts a new virtual machine and resumes it using the volatile state. –Is also in charge of termination. Service cache –Content addressable store of data chunks Remote service Virtual Machine Service Cache Director

15. data Content Addressable Cache Content Addressable Database Service Cache VM1 VNC VM2 Speech Home Server Persistent state can be - Fetched on demand - Shared between applications Surrogate data

16. The Client Proxy It Discovers surrogate discovery using UPnP It Instantiates and destroys replicas by user request (manual) It coordinates communication with each replica –Maintains event log of requests sent by the local application component –When the first reply is received, it is returned to the local components. –Replies are compared with the first reply to ensure the replicas are behaving deterministically.

17. Instantiation of a New Replica Big idea: recreate current state from –Checkpoint on the home server –Event log on the client Application level determinism Example: + + Event Log =CheckpointCurrent State Keystroke Mouse movement

18. Instantiation of a New Replica VNC client VNC proxy Home serverSurrogate 4. Checkpoint 5. Transfer volatile state and chunk table 7. Replay event log SLOW! 2. Log requests VM VNC VM VNC VM VNC 1. Instantiate new service 3. Request volatile state and chunk table 6. Service Instantiated

19. Leveraging Portable Storage VNC client VNC proxy Home serverSurrogate 2. Replay event log 1. Log requests 1. Transfer volatile state, chunk table and hash table Portable storage carries: Volatile state Content addressable database VM VNC VM VNC VM VNC

20. Outline Motivation Problem Design principles Implementation Evaluation Conclusion

21. Evaluation How much do surrogates improve interactive response time What is the perceived performance impact of instantiating a new replica? How much does the use of mobile storage reduce replica instantiation time?

22. Network Topology Surrogate Home Server 30 ms latency Internet 1.5 Mbps AP 1.5 Mbps256 Kbps Stateful service (VNC): open Word, insert text, save document and close Word Stateless service (ViaVoice) VM VNC VM VNC NISTNET Xscale-PXA250 processor 64MB DRAM, 48MB of flash 11Mb/s Cisco 350 802.11b PCMCIA Linux 2.4.19-rmk6 kernel 3.06GHz Pentium 3 RedHat Enterprise Linux

23. Benefit of Slingshot Slingshot: 2.6 times faster than remote execution

24. Instantiating the First Replica Surrogate Home Server 30 ms latency Handheld Internet 1.5 Mbps AP 1.5 Mbps256 Kbps VM VNC

25. Speech Replication with Warm Cache 3.35 분 28.06 분

26. Speech Replication with Cold Cache

27. VNC Replication with Warm Cache : Remote execution : Slingshot : Slingshot w/ microdrive : Remote execution : Slingshot

28. VNC Replication with Cold Cache

29. Instantiating Another Replica Nearby SurrogateDistant Surrogate Home Server 15 ms latency Handheld device AP 15 ms latency Internet 1.5 Mbps AP 1.5 Mbps 256 Kbps VM VNC VM VNC

30. Speech: Moving to a New Hotspot

31. : Remote execution : Without microdrive : With microdrive VNC: Moving to a New Hotspot : Remote execution : Without microdrive

32. Conclusion Slingshot –Is 2.6x faster than remote execution –Hides surrogate failure –Minimizes surrogate maintenance cost Discussions –Application determinism? How many applications guarantee this property? –Assumption Correct? Is backhaul link only 1.5 Mbps T1 Line? How long this approach would be applicable? – 실험한 환경이라면 Remote service 를 옮기는데 시간이 30 분 정도 걸리는 데 Mobile device 에 대한 서비스가 정말 가능한가 ? –SoulPad? Remote desktop 이 정말 문제 있나 ?