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

OVERVIEW BACKGROUND GOALS ARCHITECTURES FEATURES DRAWBACKS SUMMARY

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

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.

ISIS Sample Code

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

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.

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

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

JGroups Architecture

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.

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

JGroups Sample Code

Client-Server Group

Protocol Defined in XML

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.

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.

JGroups Performance & Drawbacks

ISIS Performance & Drawbacks

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

Questions?

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”

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.

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

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…