1. Replication & Fault Tolerance CONARD JAMES B. FARAON
ISIS Project & JGroups
Replication & Fault Tolerance
CONARD JAMES B. FARAON

2. OVERVIEW
BACKGROUND
GOALS
ARCHITECTURES
FEATURES
DRAWBACKS
SUMMARY

3. ISIS Project Background
Kenneth Birman, Robert Cooper, Keith Marzullo. (1980’s)
Cornell University.
Research: scalability, security, management.
Commercialized Distributed System:
Stock Exchange
Air Traffic Control
Automation
Factory Automation
Toolkit (Written in C, Lisp, etc): Virtual Synchrony Model

4. ISIS Protocols Multicast protocols: Flush protocols FBCAST: unordered
CBCAST: causally ordered
ABCAST: totally ordered
GBCAST: sync-ordered used for managing group membership
Flush protocols
Message is unstable if some receiver has it but (perhaps) others don’t.
All-to-all echo of any unstable messages to processes who have not received a copy of those messages.

5. ISIS Sample Code

6. JGroups Background Java Toolkit for reliable and flexible messaging.
Inspired by the ISIS research.
Developed by Bela Ban.
Current Stable Release: May 10, 2017.
Consists of the following:
Channels
Building Blocks
Flexible Protocol Stack

7. Virtual Synchrony (IPC) Ordered, and Reliable Multicast.
“Send to all members or to none.”
Process Groups- Programs in a network organized themselves.
Fault Tolerance
Replication using remote message passing.

8. Goal: Virtual Synchronous Toolkits for the following:
Atomic Multicast
Process groups & group communication.
Deciding how to respond to a request.
Concurrency.
Synchronization.
Replicated Data.
Failure Tolerance (Detecting and Reacting).
Dynamic configuration.
Stable Storage.
Recovery.
Transactions
Protections
Consistency

9. Process Groups Peer group. Client/Server group. Diffusion group.
Hierarchical group.

10. JGroups Architecture

11. Building Blocks Provides higher level of abstraction.
Application passes through the Building Block rather than Channel.
Saves development time. (Library for developers)
Mostly for fault tolerance and replications.
Performs Cluster-wide execution.
Performs Cluster wide locking.

12. Flexible Protocol Stack
Approximately 70 protocols available.
NAKACK
Ordering:
FIFO
SEQUENCER
CAUSAL
GMS
FAILURE_DETECTOR
STATE_TRANSFER
FRAGMENTATION
SECURITY
FLOW CONTROL
ETC.

13. JGroups Sample Code

14. Client-Server Group

15. Protocol Defined in XML

16. Replicated HashMap States are shared using a HashMap.
States are shared through serialization.
Create several instances of HashMap.
Modifications are propagated.
Listeners are notified for updates.
Read-only requests are locally invoked.

17. Replication Process Groups- share copies of the data.
State Transfer is used to initialize the joining member.
Replication using remote message passing or serialization.
Updates delivered as events.

18. JGroups Performance & Drawbacks

19. ISIS Performance & Drawbacks

20. Summary Reliability Availability ISIS uses Virtual Synchrony Model.
Message Ordering
Timeout interval
Replication using RPC
JGroups adds the following:
Building Blocks
Flexible Protocol Stack

21. Questions?

22. Appendix JGroups Channel Handle to a group. Has “view” of the channel.
Unicast
Multicast
Anycasting (TCP)
View = {A, B, C, D, E}
Dest = {C,D}
A member that crashed or failed are labeled “suspected”

23. Appendix Diffusion Group Client-Server group.
Server multicast messages to the full set of servers and clients.
Clients only receive messages.
Example: Brokerage Trading Floor.

24. Appendix Hierarchical Group Used if several groups are needed.
Tree-structured sets of groups
Group redirects request to an appropriate subgroup.

25. Appendix Building Blocks examples: MessageDispatcher
Deals with sending message requests.
Correlating message responses.
RpcDispatcher
Implements its own Serialization.
Method Lookup
May exist in multiple channels.
And many more…