1. Reliable Distributed Systems
Membership
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2. http/https 1.1 WS-Addressing SOAP1.2, MTOM XML1.1: XMLScheme,
XPath, XSL
WS-Policy,
WS-MetaDataExchange
WSDL1.2, UDDI3.0
WS-Reliability, WS-Membership
WS-Security, WS-Trust,
WS-SecureConversation
WS-Transaction,
WS-Coordination
WS-BPEL,
WS-Choreography
WS-Resource,
WS-ResourceProperties
WS-Notification,
WS-Eventing
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3. Group Membership
Foundational concept for high speed data replication protocols.
Essential for large scale grid-based virtual organizations and resource discovery and scheduling
Solution: Group membership service (GMS)
Manage GMS services’ membership and then manage other services’ general membership: 2-tier architecture
GMP Group Membership Protocol is used among GMS to manage membership
GMS then woks on its group.
Another problem is static vs dynamic membership
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4. Agreement on Membership
Detecting failure is a lost cause.
Too many things can mimic failure
To be accurate would end up waiting for a process to recover
Substitute agreement on membership
Now we can drop a process because it isn’t fast enough
This can seem “arbitrary”, e.g. A kills B…
GMS implements this service for everyone else
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5. Architecture Applications use replicated data for high availability
2PC-like protocols use membership changes instead of failure notification
Membership Agreement, “join/leave” and “P seems to be unresponsive”
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6. Architecture Application processes membership views A {A} {A,B,D}
{A,D}
{A,D,C}
{D,C}
GMS processes
join B
leave
GMS
join C X Y Z D
A seems to have failed
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7. GMS API
Guess?
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8. GMS API Three operations: Join(process-id, callback) Leave(process-id)
Monitor(process-id,callback)
GMS needs to be highly available;
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9. Example
Distributed system using the GMS is a air-traffic control system it would require itself to be reconfigured with existing processes after failure of a process.
In some cases such as in grid VO it may be fact of life; membership may be changing dynamically.
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10. WS-Membership: Failure Management in webservices world
WS-Membership .. by W.Vogels and C.Re
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