Whenever any Real Server is placed into Drain mode, it is always better to be able to control the behaviour of traffic being sent to it. The Drain Behaviour menu allows the selection of traffic behaviour on a per Virtual Service basis. Options are:
Option
Description
Persistence Driven
This is the default selection.
Whenever the user visits using the persistence session, it is extended.
With 24-hour usage, it is possible that the drain would never happen.
However, if the number of connections to the real server ever reaches 0, drain ends, persistence sessions are deleted, and all visitors get re-balanced on the next connection they make.
Migrate Visitors
Persistent session ignored on re-connect - (legacy behavior before 2022)
New TCP connections (whether part of an existing session or not) are always made to an online real server.
If the persistence session was to a draining real server, it is overwritten.
The Virtual Service will effectively ignore persistence on any new connections, and they will be load balanced to a new server.
Retire Sessions
Persistent sessions are not extended.
Incoming user connections will be allocated to their desired server, but their persistence session is not extended. So, after the persistence session time is exceeded, they will be treated as a new connection and moved to a different server.
