force-persist { if | unless } Declare a condition to force persistence on down servers May be used in sections :

defaults frontend listen backend no no yes yes yes yes yes yes By default, requests are not dispatched to down servers. It is possible to force this using "option persist", but it is unconditional and redispatches to a valid server if "option redispatch" is set. That leaves with very little possibilities to force some requests to reach a server which is artificially marked down for maintenance operations.

The "force-persist" statement allows one to declare various ACL-based conditions which, when met, will cause a request to ignore the down status of a server and still try to connect to it. That makes it possible to start a server, still replying an error to the health checks, and run a specially configured browser to test the service. Among the handy methods, one could use a specific source IP address, or a specific cookie. The cookie also has the advantage that it can easily be added/removed on the browser from a test page. Once the service is validated, it is then possible to open the service to the world by returning a valid response to health checks.

The forced persistence is enabled when an "if" condition is met, or unless an "unless" condition is met. The final redispatch is always disabled when this is used. See also : "option redispatch", "ignore-persist", "persist", and section 7 about ACL usage.