🔐 TLS Termination Models - SSL Passthrough vs SSL Termination (Offloading) vs SSL Bridging (Re-Encryption)

Why They Exist, Why They’re Used, and When Each Matters

TLS is not just “turning on HTTPS.”

Where TLS is terminated defines:

• 👁️ Who can see the traffic
• 🛡️ What security controls are possible
• 📈 How scalable your system is
• 📋 Whether auditors will sign off

That’s why multiple TLS termination models exist.

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🌐 Why TLS Termination Models Exist

Because no single model can optimize all of these at once:

• 🔐 Security
• ⚙️ Operability
• 📈 Scalability
• 🔍 Traffic visibility
• 💰 Cost efficiency

Each TLS termination model trades one dimension for another.

Understanding these trade-offs prevents:

• Over-engineered designs
• Weak security assumptions
• “Best-practice” architectures that fail in production

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1️⃣ SSL Passthrough (End-to-End TLS)

The proxy or load balancer does NOT decrypt TLS.

Encrypted traffic is forwarded directly to the backend.

Architecture Diagram

  Client
    |
    | HTTPS (TLS)
    v
Load Balancer (Layer 4 – no decryption)
    |
    | HTTPS (TLS)
    v
Backend Application (TLS terminates here)

🎯 Why It Exists

• Maintain true end-to-end encryption
• Enforce zero-trust networking
• Keep TLS fully owned by the application

🧪 Examples

• gRPC services with mTLS
• Banking and healthcare backends
• Kubernetes Ingress with SSL Passthrough enabled

✅ Why It Matters

• No intermediate system can inspect or modify traffic
• Required for strict compliance environments

⚠️ Trade-offs

• ❌ No path-based routing
• ❌ No WAF, authentication, or rate limiting
• ❌ Certificate management per backend

Best when: Security > operability

Avoid when: Traffic inspection is required

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2️⃣ SSL Termination / SSL Offloading (Most Common)

TLS is terminated at the proxy or load balancer.

Backend traffic becomes plain HTTP.

Architecture Diagram

    Client
      |
      | HTTPS
      v
Load Balancer / Reverse Proxy (TLS ends here)
      |
      | HTTP
      v
Backend Application

🎯 Why It Exists

• Centralized certificate management
• Simplified backend services
• Enables Layer-7 traffic handling

🧪 Examples

• AWS ALB / ELB
• Nginx Ingress Controller
• HAProxy, Envoy

✅ Why It Matters

TLS must be decrypted to enable:

• Path-based routing (/api, /auth)
• WAF and rate limiting
• Authentication and observability

⚠️ Trade-offs

• ❌ Backend traffic is unencrypted
• ❌ Internal network must be trusted

💡 This model powers most production SaaS platforms today.

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3️⃣ SSL Bridging / Re-Encryption (Best of Both, Costs More)

TLS terminates at the proxy, and a new TLS session is created to the backend.

Architecture Diagram

    Client
      |
      | HTTPS
      v
Proxy / Load Balancer (TLS #1 terminates)
      |
      | HTTPS (TLS #2 starts)
      v
Backend Application\

🔑 Key Characteristics

• Two TLS sessions
• Proxy can inspect traffic
• Backend still receives encrypted traffic

✅ Pros

• End-to-end encryption preserved
• Full Layer-7 features at the proxy
• Strong compliance posture

❌ Cons

• Extra CPU overhead (double TLS)
• Certificates required at both proxy and backend
• Harder debugging and troubleshooting

🧭 When to Use

• Regulated environments (PCI-DSS, HIPAA)
• Kubernetes ingress with security mandates
• Zero-trust internal networks

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❌ Common Misconceptions

SSL termination is insecure.

• False, if the internal network is controlled.

SSL passthrough is always better.

• False, if routing or inspection is required.

SSL bridging is free security.

• False — it costs CPU, latency, and operational effort.

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🧭 Practical Recommendation (No BS)

• Simple public apps / Maximum simplicity → SSL Termination
• Compliance-heavy systems / Security + control → SSL Bridging
• Strict zero-trust / mTLS / Maximum secrecy → SSL Passthrough

If you can’t clearly explain why you chose one,

you probably chose the wrong model.

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📊 Comparison Table

Feature	SSL Passthrough	SSL Termination	SSL Bridging
TLS decrypted at proxy	❌	✅	✅
Backend traffic encrypted	✅	❌	✅
HTTP routing / WAF	❌	✅	✅
Certificate management	Backend	Centralized	Both
Operational complexity	High	Low	High
Security level	🔒🔒🔒	🔒🔒	🔒🔒🔒

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🧠 Final Takeaway

SSL/TLS termination models exist because:

Security, visibility, scalability, and cost cannot all be optimized at once.

There is no universal best practice —

only context-correct architectural decisions.