You've got two internal Node services talking to each other. How do you secure that traffic, and what does mutual TLS actually buy you over regular one-way TLS?

So internal traffic should still run over TLS, so nobody on the network can read it or tamper with it. Regular one-way TLS is the server proving its identity to the client with a certificate signed by a trusted certificate authority. Mutual TLS, mTLS, goes one step further, both the client and the server present certificates, so each side verifies who the other one is. That's useful for internal services where you only want authorized callers reaching each other, not just anyone who can hit the network. You'd manage the certificates through a certificate authority, usually an internal one for internal services, and rotate them before they expire. So basically mTLS gets you mutual authentication, a service only accepts connections from clients presenting a valid certificate, which is stronger than just trusting network location.