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Tapestry: A resilient global-scale overlay for service deployment

Tapestry: A resilient global-scale overlay for service deployment. B.Y. Zhao, L. Huang, J. Stribling, S.C. Rhea, A.D. Joseph, J.D. Kubiatowicz IEEE Journal on Selected Areas in Communications, January, 2004. Tapestry. An overlay location and routing infrastructure

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Tapestry: A resilient global-scale overlay for service deployment

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  1. Tapestry: A resilient global-scale overlay for service deployment B.Y. Zhao, L. Huang, J. Stribling, S.C. Rhea, A.D. Joseph, J.D. Kubiatowicz IEEE Journal on Selected Areas in Communications, January, 2004

  2. Tapestry • An overlay location and routing infrastructure • provides location-independent routing of messages directly to the closest copy of an object or service • using only point-to-point links and without centralized resources • Based on Plaxton mesh • Routing and directory information is purely soft state and easily repaired • Self-organizing, fault-resilient, and load-balancing

  3. nodeIDs, GUIDs and Aid • Nodes in the overlay are assigned nodeIDs • uniformly at random from a large identifier space • more than one node may be hosted by one physical host • Application-specific endpoints are assigned Globally Unique IDentifiers (GUIDs) • selected from the same identifier space • node N has nodeID Nid, and an object O has GUID OG • To enable application coexistence, every message contains an application-specific identifier, Aid

  4. Identifier Space • Currently uses an identifier space of 160-bit values with a globally defined radix (e.g., hexadecimal, yielding 40-digit identifiers) • nodeIDs and GUIDs are assumed roughly evenly distributed in the namespace • can be achieved by using a secure hashing algorithm like SHA-1

  5. Networking APIs 1) PUBLISHOBJECT(OG, Aid): Publish, or make available, object O on the local node. This call is best effort, and receives no confirmation 2) UNPUBLISHOBJECT(OG, Aid): Best-effort attempt to remove location mappings for O 3) ROUTETOOBJECT(OG, Aid): Routes message to location of an object with GUID OG 4) ROUTETONODE(N, Aid, Exact): Route message to application Aid on node N. “Exact” specifies whether destination ID needs to be matched exactly to deliver payload

  6. Neighbor Map • Route overlay messages to the destination ID digit by digit • 4XXX  42XX  42AX  42AD • Multiple levels • each level represents a matching suffix up to a digit position in the ID • Contains a number of entries equal to the ID’s base • ith entry in the jth level is the ID and location of the closest node that begins with prefix (N, j -1 ) + “i”

  7. Neighbor Map in node “4227” N: 4227 i: 4, j: 3 (N, 2): 42 Prefix (424)

  8. Tapestry Routing Mesh

  9. Path of a Message: from “5230” to “42AD”

  10. Path Length • The router for the nth hop shares a prefix of length ≧ n with the destination ID • looks in its (n+1) th level map for the entry matching the next digit in the destination ID • Node will be reached in at most logβN logical hops • N: namespace size, β: IDs base • Surrogate routing • when a digit cannot be matched, Tapestry looks for a “close” digit in the routing table

  11. Expected Total Number of Entries • Neighbors share the same prefix to help provide resilience (route reliability, faulty node prevention) • c * β* logβN • c: number of neighbors

  12. Tapestry Object Publish: Object “4378” to Node “4377” 4377 Publish Path Location Mapping 437A 43FE 4228 Tapestry Pointer 4361 4664 Phil’s Books (4378) 4B4F 4A6D Phil’s Books (4378) E791 57EC AA93

  13. Tapestry Route to Object

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