Monitoring firewall logs would show calls to suspicious IPs and domains after you pulled the Docker container. A MiTM attack is usually conducted between two communicating parties, rather than inside the server itself. The attacker intercepts traffic as it travels across a network or service path. MiTM are not always done exterior of the server, but usually. Strong ciphers are your friend. Although MiTM and PIC events can overlap, a PIC is usually an attacker gaining unauthorized access to a system. A PIC compromise occurs outside the public facing server, through a stolen administrator password, compromised developer workstation, exposed API key, or hijacked cloud account. Securing API, devices, frequent password rotation are good practices. Again, not always exterior of the server, but usually.