Gozar: NAT friendly Peer Sampling with One Hop Distributed NAT Traversal

Transcription

1 Gozar: NAT friendly Peer Sampling with One Hop Distributed NAT Traversal Amir H. Payberah Jim Dowling Seif Haridi 1

2 Introduction 2

3 Gossip based Peer Sampling Service Gossip based peer sampling services (PSS) have been widely used in large scale distributed applications. Information dissemination Aggregation Overlay topology management A PSS provides a node with a uniform random sample of live nodes from all nodes in the system (partial view). 3

4 Gossip based Peer Sampling Protocol (1/7) 0 n2 n9 1 n8 n4 n7 n6 4

5 Gossip based Peer Sampling Protocol (2/7) n9 n8 0 n8 n7 0 1 n6 1 n2 n4 n7 n6 5

6 Gossip based Peer Sampling Protocol (3/7) n9 n8 0 n8 n7 0 1 n8 n7 shuffle request n6 1 n2 n4 n7 n6 6

7 Gossip based Peer Sampling Protocol (4/7) n9 n8 0 n8 n7 0 1 n6 shuffle response n8 n7 n6 1 n2 n4 n7 n6 7

8 Gossip based Peer Sampling Protocol (5/7) n9 n8 0 n6 n8 n7 0 1 n8 n7 n6 1 n2 n4 n7 n6 8

9 Gossip based Peer Sampling Protocol (6/7) n9 n8 0 Update State n6 n8 n7 0 1 n8 n7 Update State n6 1 n2 n4 n7 n6 9

10 Gossip based Peer Sampling Protocol (7/7) n9 n8 0 n8 n7 n6 0 1 n8 n7 1 n2 n4 n7 n6 10

11 Gossip based Peer Sampling Design Space Peer Selection View Exchange View Merge 0 n2 n9 1 n8 n4 n7 n6 11

12 Peer Selection Gossip based Peer Sampling Design Space Random Tail 0 n2 View Exchange Push n9 1 Push Pull n8 n4 View Merge Blind n7 n6 Healer Swapper 12

13 Problem Description 13

14 NAT Environments (1/4) Private node 1 n2 0 n4 n9 shuffle request n8 n6 Public node n7 14

15 NAT Environments (1/4) Private node 1 n2 0 n4 n9 shuffle response n8 n6 Public node n7 15

16 NAT Environments (1/4) Update State Private node 1 n2 0 n4 n9 shuffle response n8 n6 Update State Public node n7 16

17 NAT Environments (1/4) Private node 1 n2 0 n4 n9 shuffle request n8 n6 Public node n7 17

18 Impact of NATs on PSS' (1/2) Size of the biggest cluster for an increasing percentage of NATs. [A.M.Kermarrec ICDCS'09] 18

19 Impact of NATs on PSS' (2/2) Ratio of non stale references to private nodes. [A.M.Kermarrec ICDCS'09] 19

20 Solutions for Communicating with Private Nodes (1/3) Relay communications to the private node using a public relay node. 20

21 Solutions for Communicating with Private Nodes (2/3) Use a NAT hole punching algorithm to establish a direct connection to the private node using a public rendezvous node. 21

22 Solutions for Communicating with Private Nodes (3/3) Route the request to private nodes using chains of existing open connections (of unbounded length). 22

23 Research Challenges for a NAT friendly PSS Assuming distributed relay and rendezvous services, how do nodes discover which public nodes act as partners for the private nodes? Is hole punching or relaying preferable for communicating with private nodes? How much data will be sent over the connection and what are the latency requirements? How fairly should the gossiping load be balanced over public versus private nodes? 23

24 Gozar NAT friendly Peer Sampling Service 24

25 Design Space Peer Selection Rand Tail View Propagation Push Push Pull View Selection Blind Healer Swapper 25

26 Design Space Peer Selection Rand Tail View Propagation Push Push Pull Gozar View Selection Blind Healer Swapper 26

27 NAT Friendliness in Gozar In Gozar, each private node connects to one or more public nodes, called partners that act as a relay or rendezvous server on behalf of the private node. A node's descriptor consists of both its own address, its NAT type, and its partners' addresses at the time of descriptor creation. When a node wants to gossip with a private node, it uses the partner addresses in its descriptor to communicate with the private node. 27

28 Partnering (1/10) Bootstrap server n2 n4 28

29 Partnering (2/10) Bootstrap server n2 n4 29

30 Partnering (3/10) Bootstrap server n2, public, null n4, public, null n4 30

31 Partnering (4/10) Bootstrap server request n2, public, null n4, public, null n4 request 31

32 Partnering (5/10) Bootstrap server ACK n2, public, null n4, public, null n4 NACK 32

33 Partnering (6/10) Bootstrap server n2, public, null n4, public, null n4 33

34 Partnering (7/10) Bootstrap server n2, public, null n4, public, null Shuffle exchange n4 n2, private, 34

35 Partnering (8/10) Bootstrap server n2, public, null n4, public, null n4 Shuffle exchange n2, private, n2, private, 35

36 Partnering (9/10) Bootstrap server n2, public, null n4, public, null Shuffle request n4 n2, private, n2, private, 36

37 Partnering (10/10) Bootstrap server n2, public, null n4, public, null Shuffle response n4 n2, private, n2, private, 37

38 Relaying or Hole Punching? Relaying? Lower latency message exchange. Enables lower gossip cycle periods. Necessary in dynamic networks Hole punching? Decreases load on public nodes. But not if shuffle messages are small. Applications that use the PSS can use partners to hole punch or relay messages to private nodes. 38

39 Experiments 39

40 Experiment Setup Using the Kompics as a simulator platform. King dataset is used to model the latencies between nodes nodes, 80% of nodes are private and 20% are public. Compare with Nylon and ARRG. Cyclon is used as a baseline. 40

41 Metrics Randomness properties: Local randomness In degree distribution Clustering coefficient Avg. path length Protocol overhead. Fairness and connectivity in catastrophic failure. 41

42 Randomness 42

43 Protocol Overhead 43

44 Fairness and Connectivity in Failure 44

45 Conclusions 45

46 Conclusions Gozar is a NAT friendly gossip based peer sampling service that also provides a distributed NAT traversal service to clients of the PSS. Public nodes are leveraged to provide both the relaying and hole punching services. Relaying is only used for gossiping to private nodes lower connection latency Enabling a faster gossiping cycle The messages relayed are small 46

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