Design and implementation of a group membership protocol.

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by  Raghuram, Devalla.;Shukla, Shridhar B.

DUDU
POSTGRADUATESCHOOL
liAVAL
MONTEREY. CALIFORNIA93943-5002

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DESIGN AND IMPLEMENTATION OF A GROUP MEMBERSHIP PROTOCOL
12. PERSONAL AUTHOR(S)
Raghuram Devalla
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Master's Thesis from 09/90 to 09/92 September 1992 12'
16. SUPPLEMENTARY NOTATION The views expressed in this thesis are those of the author and do not reflect the
official policy or position of the Department of Defense or the United States Government.
17. COSATI CODES 18. SUBJECT TERMS (Continueon reverse ifnecessary and identify by block number)
FIELD GROUP SUB—GROUP
Distributed processing, Group membership problem, Process groups.
19. AABSgTrRoAuCpT m(eComnbteirnusehoinprpevreortsoecioflneecnessusarreysaangdriedeenmteinfytbaynbdloccoknnsiusmtbeenrt)commit actions among group members to maintain a sequence!
of identical group views in spite of continuous changes, either voluntary or otherwise, in processors' membership status. In
asynchronous distributed environments, such consistency among group views must be guaranteed using messages over a network!
which does not bound message delivery times. Assuming a network that only provides a reliable, FIFO channel between any pairj
of processors, one approach to designing such a protocol is to centralize the responsibility to detect changes, ensure agreement.
and commit them consistently in a single manager process. This approach is complicated by the fact that a protocol to elect aj
new manager with a consistent membership proposal must be executed when the manager itselffails. In this thesis, a membership!
protocol based on orderingofgroup members in a logical ring that eliminates the need for such centralized responsibility is presented
Agreement and commit actions are token-based and the protocol ensures that no tokens are lost or duplicated due to changes in!
membership. It is able to process continuous changes to the membership, does not depend upon any majority-based decisions.!
and processes joins and departures identically. The cost of committing a change is always 2n point-to-point messages over FIFOj
channels where n is the group size. The protocol correctness is proven in a formal framework. The implementation details for thel
protocol to execute on a network of SUN workstations is presented. Detailed examples of the behavior of the protocol for various!
sequences of changes to group membership is presented. The programs for various client-server communication patterns used foi!
interfacing various functions are also presented.
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Shridhar B Shukla [phone] Ec/Sh
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Design and Implementation
of a
Group Membership Protocol
by
Raghuram Devalla
DoD
Scientist, India
B.E, Indian Institute of Science, 1983
Submitted in partial fulfillment of the
requirements for the degree of
MASTER OF SCIENCE IN SYSTEMS ENGINEERING
from the
NAVAL POSTGRADUATE SCHOOL
September 1992
ABSTRACT
A group membership protocol ensures agreement and consistent commit actions
among group members to maintain a sequence of identical group views in spite of
continuous changes, either voluntary or otherwise, in processors' membership status.
In asynchronous distributed environments, such consistency among group views must
be guaranteed using messages over a network which does not bound message delivery
times. Assuming a network that only provides a reliable, FIFO channel between
any pair of processors, one approach to designing such a protocol is to centralize the
responsibility to detect changes, ensure agreement, and commit them consistently in
a single manager process. This approach is complicated by the fact that a protocol to
elect a new manager with a consistent membership proposal must be executed when
the manager itself fails. In this thesis, a membership protocol based on ordering
of group members in a logical ring that eliminates the need for such centralized
responsibility is presented. Agreement and commit actions are token-based and the
protocol ensures that no tokens are lost or duplicated due to changes in membership.
It is able to process continuous changes to the membership, does not depend upon any
majority-based decisions, and processes joins and departures identically. The cost of
committing a change is always 2n point-to-point messages over FIFO channels where
n is the group size. The protocol correctness is proven in a formal framework. The
implementation details for the protocol to execute on a network of SUN workstations
are presented. Detailed examples of the behavior of the protocol for various sequences
of changes to group membership is presented. The programs for various client-server
communication patterns used for interfacing various functions are also presented.
111
1)1'
C.I
TABLE OF CONTENTS
INTRODUCTION
I. 1
BACKGROUND
A. 1
OBJECTIVES OF THE STUDY
B. 2
C. THESIS ORGANIZATION 3
II. EXISTING APPROACHES 4
GROUP MEMBERSHIP PROBLEM
A. 4
1. Importance 4
2. System Classification 5
SYNCHRONOUS SYSTEMS
B. 6
1. Periodic Broadcast Protocol 6
2. Attendance List Protocol 7
3. Robust Group Membership Algorithm 7
ASYNCHRONOUS SYSTEMS
C. 8
1. Failure Detection and Notification Protocol 8
2. Protocol Based on Total Message Ordering 10
3. Protocol Based on Rotating Token List 11
4. ISIS Approach 12
GROUP MEMBERSHIP PROTOCOL
III. 14
A. ASSUMPTIONS, OVERVIEW, AND DEFINITIONS 15
1. Overview 16
a. Processing of Individual Changes 18
2. Definitions 19
a. Group Membership Problem Definition 19
iv
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NAVALPOSTGRADUATESCHOOL
IFORNIA93943-5002
b. Logical Ring 20
c. Tokens 21
d. Neighbor and Host Computation 22
THE MEMBERSHIP PROTOCOL
B. 23
1. Status Change Detection and Agreement Initiation 24
2. The Agreement Phase 25
3. The Commit Phase 27
a. Effects of a Commit Action 27
b. Ensuring an Identical Sequence of Commits 28
CORRECTNESS OF THE PROTOCOL
C. 29
IMPLEMENTATION OF THE PROTOCOL
IV. 35
A. PROTOCOL SOFTWARE DESIGN 35
1. Functions in the Protocol 35
MP
2. Subcomponents of 37
B. DATA STRUCTURE DEFINITIONS 37
C. PROCESS SPECIFICATIONS 46
1. FIFO-Channel-Layer 46
2. Initiate-Departure 49
3. Initiate-Join 53
4. Agreement Process 54
5. Commit Process 56
6. TokenPool Manager 58
7. StatusTable Manager 61
8. GroupView Manager 61
9. Join Initial 62
D. IMPLEMENTATION ON UNIX MACHINES 63
v
1. Pipes 64
2. FIFOs 65
3. Message Queues 66
4. Sockets 68
5. Transport Layer Interface 69
AN EXAMPLE
V. 71
A. INITIAL CONDITIONS 71
EXPLANATION OF THE EXAMPLE
B. 72
1. Failure of a Single Member 72
2. Join of a Single Member 75
3. Multiple Failures and Joins 75
CONCLUSIONS AND FUTURE DIRECTIONS
VI. 81
CONCLUSIONS
A. 81
FUTURE WORK
B. 81
APPENDIX A
82
GROUPVIEW SERVER
A. 82
. .
TOKENPOOL SERVER
B. 90
C. STATUS TABLE SERVER 97
D. COMMIT PROCESS SERVER 105
REFERENCES
113
INITIAL DISTRIBUTION LIST 115
VI