Custom Persistence with DataScript

Description

Avi Vantage includes a number of common methods of persisting clients to the same server for a duration of time. For some applications, it may be valuable to have more customization to the behavior of the persistence, or to support a wider array of application types. See Overview of Server Persistence for other methods.

Persistence is based on the ability to uniquely identify a user, and to stick or persist them to a destination server for a period of time.

The primary DataScript function for creating custom persistence are the table commands, which enable storing data locally on an Avi Service Engine for a configurable length of time. The stored data is also replicated to other relevant Service Engines for high availability and scale.

DataScript

avi.vs.table_insert( [table_name,] key, value [, lifetime] )	Store custom data in a time-based table
avi.vs.table_lookup( [table_name,] key [, lifetime_exten] )	Lookup data in a table
avi.vs.table_remove( [table_name,] key )	Remove data from a table
avi.vs.table_refresh( [table_name,] key [, lifetime_exten] )	Update the expire time for a table entry

JSessionID Example

The following example persists based upon an HTTP cookie sent from a server with a unique JSessionID. Subsequent client requests include that cookie, which is used to persist requests to the same server.

HTTP Response event: Add persist for 20 minutes, or update timer if entry already exists

if avi.http.get_cookie("JSESSIONID") then
  avi.vs.table_insert(avi.http.get_cookie("JSESSIONID"), avi.pool.server_ip(), 1200)
end

HTTP Request event: Rename the pool before applying to a virtual service

if avi.http.get_cookie("JSESSIONID") then
  avi.pool.select("poolname", avi.vs.table_lookup(avi.http.get_cookie("JSESSIONID")))
end