Reliable Distributed Systems

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Reliable Distributed Systems

• Membership

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(No Transcript)
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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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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 isnt fast
  enough
• This can seem arbitrary, e.g. A kills B
• GMS implements this service for everyone else

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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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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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GMS API

• Guess?

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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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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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WS-Membership Failure Management in webservices
world

• WS-Membership .. by W.Vogels and C.Re