webserivce request to F5 pool cannot be Forced offline

It has the option Action on Service Down, I have used it for a long time and it works very well.

"Action on Service Down" is a Pool setting, and can be found in the GUI (Local Traffic -> Pools). Choose "Advanced" in the Configuration dropdown to reveal the "Action on Service Down" setting.

The possible options are None, Reject, Drop, Reselect

Use "Reject" when you want LTM to explicitly close both sides of the connection when the server goes DOWN. "Reject" is the most commonly used option for the service down setting. This option often results in the quickest recovery of a failed connection since it forces the client side of the connection to close, in many cases triggering an automatic re-connect & re-send of the request in process.

Use "Drop" when sending a RST to the client is not desirable. This method does not immediately reflect the server's state change to the client, and depends on the client to close or otherwise manage the connection.

Use "Reselect" when the client can continue with a new server seamlessly. The request in play at the time of state transition may be lost, so the client will need to be able to recover gracefully to use this option successfully.

Use "None" if you don't want LTM to intervene in managing either side of the connection. Useful if your servers may not be accepting new connections, but should be allowed to continue servicing existing connections when marked DOWN. Also supports custom monitoring designed to support connection bleeding and other non-standard state management schemes.

In environments that I set up I usually use the Reject option, however, each one should analyze what fits best in their environment.