https monitor with un-trusted certificate

Try adding -k while running curl to allow insecure connections and verify REGISTERED is returned.

Yes, if I add the -k switch to CURL I see what I expect in my RECEIVE field.

f5 server-side SSL generally don't care about the server certificate as long as there is one. it could be a cipher compatibility issue, or your SEND string could be off. Did you test the GET in curl using a server-IP or the hostname?

Try adding another \r\n to terminate get request; might be your server requires HTTP 1.0 compliant requests.

ie: SEND:"GET /application/api/status\r\n\r\n"

thanks everyone, i figured it out. I assumed it was the untrusted SSL certificate that was the issue but it was how the SEND string was formatted. I ended up using:

GET /application/api/status HTTP/1.1\r\nHost: LB-FQDN\r\nConnection: close\r\n\r\n

and that resolved it. Thanks for your help.

This is a handy solution article for building HTTP requests for monitors - https://support.f5.com/kb/en-us/solutions/public/2000/100/sol2167.html