I use HTTP sensors to monitor various external webpages. Some of these sensors fail to check their target websites successfully. For example, I get the following HTTP sensor errors, depending on the monitored webpage and when SNI is used for the SSL handling:
- Application protocol errors: 403 Forbidden, 400 Bad Request
- SSL/TLS protocol errors: Failed to establish secure connection, error connecting with SSL, SSL handshake failure
What can be the reason for these protocol errors? Why do I get SSL handshake failures?