RSA Certificate & Key question

Sure. The questions asked were to attempt to understand the challenges. id_rsa keys are not used for TLS traffic, so you would not apply these to BIG-IP SSL profiles. You would normally use this type of key for SSH remote access to some system. You could also see these keys used in an AFM SSH proxy configuration:

• https://support.f5.com/csp/article/K27335364
• https://techdocs.f5.com/en-us/bigip-15-1-0/big-ip-network-firewall-policies-and-implementations/afm-protocol-security/ssh-protocol-security/authenticating-ssh-proxy-traffic/defining-ssh-proxy-password-or-keyboard-interactive-authentication.html

You might have also used id_rsa keys for SSH public key auth to the BIG-IP: https://support.f5.com/csp/article/K13454

Here's some additional information you might find useful regarding TLS certs/keys:

• BIG-IP SSL administration: https://techdocs.f5.com/en-us/bigip-15-1-0/big-ip-system-ssl-administration.html
• Overview of client SSL profiles: https://support.f5.com/csp/article/K14783
• Overview of server SSL profiles: https://support.f5.com/csp/article/K14806
• Managing BIG-IP SSL certificates and keys: https://support.f5.com/csp/article/K17379

Otherwise, AD remote user logon (to the BIG-IP) does not use id_rsa (SSH) keys: https://techdocs.f5.com/en-us/bigip-17-0-0/big-ip-systems-user-account-administration/remote-user-account-management.html