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Spring / Spring gRPC Interview Questions

What is mTLS and why is it commonly used for internal gRPC service-to-service communication?

Mutual TLS extends normal TLS so that both parties present and validate certificates, not just the server. This gives two-way authentication (each side proves who it is) plus the usual encryption-in-transit guarantees of TLS.

sequenceDiagram
  participant C as Client Service
  participant S as Server Service
  C->>S: ClientHello
  S-->>C: ServerHello + server cert
  C->>S: client cert
  S-->>C: validate client cert, accept
  Note over C,S: Encrypted, mutually authenticated channel established

It's popular in microservice/service-mesh environments (often provisioned automatically by a mesh like Istio or Linkerd) because it authenticates services to each other without embedding long-lived, easily-leaked shared tokens in configuration - identity is instead tied to short-lived, rotated certificates managed by the mesh's control plane.

What does mTLS add compared to standard one-way TLS?
Why is mTLS attractive for internal service-to-service gRPC traffic in a mesh environment?

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