Nortel Web OS 10.0, Application Manual

Page: 429 / 482

Web OS 10.0 Application Guide
Chapter 16: Persistence
n
429
212777-A, February 2002
Rewrite Cookie Mode
In rewrite cookie mode, the Web switch generates the cookie value on behalf of the server,
eliminating the need for the server to generate cookies for each client.
Instead, the server is configured to return a special persistence cookie which the switch is con-
figured to recognize. The switch then intercepts this persistence cookie and rewrites the value
to include server-specific information before sending it on to the client. Subsequent requests
from the same client with the same cookie value are sent to the same real server.
Rewrite cookie mode requires at least eight bytes in the cookie header. An additional eight
bytes must be reserved if you are using cookie-based persistence with Global Server Load Bal-
ancing (GSLB).
N
OTE
–
Rewrite cookie mode only works for cookies defined in the HTTP header, not cookies
defined in the URL.
Example: The following figure shows rewrite cookie mode operation:
Figure 16-4 Rewrite Cookie Mode
N
OTE
– When the Web switch rewrites the value of the cookie, the rewritten value represents
the responding server; that is, the value can be used for hashing into a real server ID or it can
be the real server IP address. The rewritten cookie value is encoded.
Internet
1. Configure switch to rewrite cookie values
Web Server
Farm
Client
Web Switch
Proxy Firewall
2. Client visits the Web site via HTTP request
3. Switch selects
server via SLB
4. Server HTTP response
includes empty cookie
5. Web switch rewrites the cookie to contain a
server ID for hashing on subsequent requests