Architecture

Client 1 Client 2

• • •Client 3

Secondary Site(cluster)

Primary Sitewww.eScent.com

(cluster)Secondary Site

(cluster)

Communication

1. HTTP(TPC): www.eScent.com

IP: xxx.xxx.xxx.xxx

PrimaryCluster

4. HTTP(TCP): <frameset...eScent_y.com...>

SecondaryCluster

x

SecondaryCluster

y

SecondaryCluster

z

2. UDP: Request fromIP xxx.xxx.xxx.xxx

2. UDP: Request fromIP xxx.xxx.xxx.xxx

2. UDP: Request fromIP xxx.xxx.xxx.xxx

3. UDP:Ping = x

3. UDP:Ping = y

3. UDP:Ping = z

5. HTTP(TCP): eScent_y.com

ping

ping

ping A typical sequence of events:

1. The client requests a connection towww.eScent.com (which points to the primary clusterR)

2. R notifies all secondary clusters about the requestvia UDP (also possible by TPC, GMS, but notnecessary)

3. Secondary clusters ping the client and calculateround-trip latencies, sending them back to R.

4. R chooses between the first several responses anddirects the client to one of the secondary clusters.

Advantages:

1. Multicasting client requests through UDP proves tobe fast, efficient and with very small overhead(Reliability). Also helps for updating the distributeddatabase (no need to close sites!).

2. Framesets ensure that even in case of secondarycluster failure, the client will be connected to anotherone with minimum losses, like shopping baginformation (Availability).

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