Byzan&ne Fault Tolerance CS 425: Distributed Systems Fall 2011 - - PowerPoint PPT Presentation

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Byzan&ne Fault Tolerance CS 425: Distributed Systems Fall 2011 - - PowerPoint PPT Presentation

Aug 30, 2023 277 likes •624 views

Byzan&ne Fault Tolerance CS 425: Distributed Systems Fall 2011 Material drived from slides by I. Gupta and N.Vaidya 1 Reading List L. Lamport, R. Shostak, M. Pease, The Byzan&ne Generals Problem, ACM ToPLaS 1982. M.

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SLIDE 1

Byzan&ne Fault Tolerance

CS 425: Distributed Systems Fall 2011

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Material drived from slides by I. Gupta and N.Vaidya

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SLIDE 2

Reading List

  • L. Lamport, R. Shostak, M. Pease, “The

Byzan&ne Generals Problem,” ACM ToPLaS 1982.

  • M. Castro and B. Liskov, “Prac&cal Byzan&ne

Fault Tolerance,” OSDI 1999.

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SLIDE 3

Byzan&ne Generals Problem

A sender wants to send message to n‐1 other peers

  • Fault‐free nodes must agree
  • Sender fault‐free  agree on its message
  • Up to f failures
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SLIDE 4

Byzan&ne Generals Problem

A sender wants to send message to n‐1 other peers

  • Fault‐free nodes must agree
  • Sender fault‐free  agree on its message
  • Up to f failures
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SLIDE 5

S 3 2 1

v v

v

Byzan&ne Generals Algorithm

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value v Faulty peer

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SLIDE 6

S 3 2 1

v v

v

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value v v

v

Byzan&ne Generals Algorithm

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SLIDE 7

S 3 2 1

v v

v

7

value v v

v ? ?

Byzan&ne Generals Algorithm

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SLIDE 8

S 3 2 1

v v

v

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value v

v

v

v ?

v

?

Byzan&ne Generals Algorithm

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SLIDE 9

3 2

v v

v

9

value v

x

v v ? v ? [v,v,?] [v,v,?]

S 1

Byzan&ne Generals Algorithm

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SLIDE 10

3 2

v v

v

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value v

x

v v ? v ? v v

S 1

Majority vote results in correct result at good peers

Byzan&ne Generals Algorithm

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SLIDE 11

S 3 2 1

v w

x

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Faulty source

Byzan&ne Generals Algorithm

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SLIDE 12

S 3 2

v w x

12

w w

1

Byzan&ne Generals Algorithm

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SLIDE 13

S 3 2

v w

x

13

x

w w v x v

1

Byzan&ne Generals Algorithm

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SLIDE 14

S 3 2

v w

x

14

x

w w v x v

1

[v,w,x] [v,w,x] [v,w,x]

Byzan&ne Generals Algorithm

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SLIDE 15

S 3 2

v w

x

15

x

w w v x v

1

[v,w,x] [v,w,x] [v,w,x] Vote result iden&cal at good peers

Byzan&ne Generals Algorithm

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SLIDE 16

Known Results

  • Need 3f + 1 nodes to tolerate f failures
  • Need Ω(n2) messages in general

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SLIDE 17

Ω(n2) Message Complexity

  • Each message at least 1 bit
  • Ω(n2) bits “communica&on complexity” to

agree on just 1 bit value

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SLIDE 18

Prac&cal Byzan&ne Fault Tolerance

  • Computer systems provide crucial services
  • Computer systems fail

– Crash‐stop failure – Crash‐recovery failure – Byzan&ne failure

  • Example: natural disaster, malicious afack,

hardware failure, sogware bug, etc.

  • Need highly available service

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Replicate to increase availability

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SLIDE 19

Challenges

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Request A Request B Client Client

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SLIDE 20

Requirements

  • All replicas must handle same requests

despite failure.

  • Replicas must handle requests in iden&cal
  • rder despite failure.

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SLIDE 21

Challenges

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2: Request B 1: Request A Client Client

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SLIDE 22

State Machine Replica&on

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2: Request B 1: Request A 2: Request B 1: Request A 2: Request B 1: Request A 2: Request B 1: Request A Client Client

How to assign sequence number to requests?

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SLIDE 23

Primary Backup Mechanism

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Client Client 2: Request B 1: Request A

What if the primary is faulty?

Agreeing on sequence number Agreeing on changing the primary (view change) View 0

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SLIDE 24

Normal Case Opera&on

  • Three phase algorithm:

– PRE‐PREPARE picks order of requests – PREPARE ensures order within views – COMMIT ensures order across views

  • Replicas remember messages in log
  • Messages are authen&cated

– {.}σk denotes a message sent by k

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SLIDE 25

Pre‐prepare Phase

Primary: Replica 0 Replica 1 Replica 2 Replica 3 Request: m {PRE‐PREPARE, v, n, m}σ0 Fail

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SLIDE 26

Prepare Phase

Request: m PRE‐PREPARE Primary: Replica 0 Replica 1 Replica 2 Replica 3 Fail Accepted PRE‐PREPARE

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SLIDE 27

Prepare Phase

Request: m PRE‐PREPARE Primary: Replica 0 Replica 1 Replica 2 Replica 3 Fail {PREPARE, v, n, D(m), 1}σ1 Accepted PRE‐PREPARE

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SLIDE 28

Prepare Phase

Request: m PRE‐PREPARE Primary: Replica 0 Replica 1 Replica 2 Replica 3 Fail {PREPARE, v, n, D(m), 1}σ1 Accepted PRE‐PREPARE Collect PRE‐PREPARE + 2f matching PREPARE

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SLIDE 29

Commit Phase

Request: m PRE‐PREPARE Primary: Replica 0 Replica 1 Replica 2 Replica 3 Fail PREPARE {COMMIT, v, n, D(m)}σ2

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SLIDE 30

Commit Phase (2)

Request: m PRE‐PREPARE Primary: Replica 0 Replica 1 Replica 2 Replica 3 Fail PREPARE COMMIT Collect 2f+1 matching COMMIT: execute and reply

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SLIDE 31

View Change

  • Provide liveness when primary fails

– Timeouts trigger view changes – Select new primary (= view number mod 3f+1)

  • Brief protocol

– Replicas send VIEW‐CHANGE message along with the requests they prepared so far – New primary collects 2f+1 VIEW‐CHANGE messages – Constructs informa&on about commifed requests in previous views

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SLIDE 32

View Change Safety

  • Goal: No two different commifed request

with same sequence number across views

Quorum for Commifed Cer&ficate (m, v, n) At least one correct replica has Prepared Cer&ficate (m, v, n) View Change Quorum

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SLIDE 33

Related Works

Fault Tolerance Fail Stop Fault Tolerance Paxos 1989 (TR) VS Replica&on PODC 1988 Byzan&ne Fault Tolerance Byzan&ne Agreement Rampart TPDS 1995 SecureRing HICSS 1998 PBFT OSDI ‘99 BASE TOCS ‘03 Byzan&ne Quorums Malkhi‐Reiter JDC 1998 Phalanx SRDS 1998 Fleet ToKDI ‘00 Q/U SOSP ‘05 Hybrid Quorum HQ Replica&on OSDI ‘06

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