Health check fails on HTTPS, even though port is open

You can also try to run this command to see if there's a problem with the handshake and see what cipers that's accepted.

echo "Q" | openssl s_client -connect www.site.com:443

Perhaps your server SSL profile has an incompatible accepted ciphers string? Or perhaps the web service uses a client certificate?

You can test the default cipher by running this command (this cipher string is the default from 11.5.0-11.5.3):

echo "Q" | openssl s_client -connect www.site.com:443 -cipher '!SSLv2:!SSLv3:!MD5:!EXPORT:RSA+AES:RSA+3DES:RSA+RC4:ECDHE+AES:ECDHE+3DES:ECDHE+RC4'

You can find the default ciphers here: https://support.f5.com/kb/en-us/solutions/public/13000/100/sol13171.html

/Patrik