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Introducing mTLS for Application Load Balancer

Networking & Content Delivery Blog



This article introduces a new feature on AWS Application Load Balancer (ALB) that allows for mutual TLS (mTLS) authentication between clients and the ALB. It explains the concepts of mTLS and how it enhances security by requiring both the client and server to authenticate each other using X.509 certificates.

Specifically, the article covers:

  • mTLS concepts like Certificate Authority, TLS certificates, certificate chain of trust, TLS handshake, and Certificate Revocation List (CRL)
  • Two modes of mTLS operation with ALB:
    • mTLS verify mode: ALB verifies client certificates using a trust store and either allows or blocks requests
    • mTLS passthrough mode: ALB forwards the client certificate chain to backend targets for authentication
  • Monitoring and CloudWatch metrics for mTLS on ALB
  • Comparison of ALB's mTLS modes with Network Load Balancer (NLB)
  • Conclusion highlighting use cases for each mTLS mode and pricing considerations


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