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A microservice fails to establish Mutual TLS with another service. The error logs show "certificate unknown". What is the most likely cause?

medium📝 Analysis Q14 of 15
Microservices - Service Mesh
A microservice fails to establish Mutual TLS with another service. The error logs show "certificate unknown". What is the most likely cause?
AThe service's certificate is not signed by a trusted CA
BThe service is using HTTP instead of HTTPS
CThe private key is missing from the service
DThe service is using a self-signed certificate but trusts it
Step-by-Step Solution
Solution:

  1. Step 1: Analyze the error "certificate unknown"

    This error means the certificate presented is not recognized or trusted by the other service.

  2. Step 2: Identify cause related to trust

    If the certificate is not signed by a trusted CA, the other service will reject it as unknown.

  3. Final Answer:

    The service's certificate is not signed by a trusted CA -> Option A

  4. Quick Check:

    Untrusted CA = certificate unknown error [OK]
Quick Trick: Certificate unknown means untrusted CA signature [OK]
Common Mistakes:
MISTAKES
  • Confusing HTTP usage with certificate errors
  • Assuming missing private key causes this error
  • Believing self-signed certs are trusted by default

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