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Chapter 5

Standing at the Door

Metaphor: A doorman / receptionist Mental image: “Let me check that for you.”

Key Ideas

This is the pivotal chapter where we introduce the concept of intermediaries — specifically the reverse proxy. This is also where Sentinel naturally fits into the story, though the chapter shouldn’t feel like a pitch.

Core concepts to cover:

  1. Not every request should go straight to the server

    • Sometimes you want someone at the door first
    • Reasons: security, efficiency, routing, inspection
    • This isn’t paranoia — it’s practical hospitality

  2. What is a reverse proxy?

    • A program that receives requests on behalf of the server
    • It can decide what to do: pass it through, reject it, modify it, route it
    • From the browser’s perspective, the proxy is the server

  3. The doorman metaphor

    • Visitors arrive at a building; the doorman greets them
    • Some are let through immediately
    • Some are asked to wait, or turned away
    • The doorman doesn’t own the building — they protect and manage access

  4. Why you might want one

    • Security: block malicious requests before they reach your server
    • Load balancing: distribute visitors across multiple servers
    • Caching: serve common pages without bothering the server
    • TLS termination: handle encryption at the edge (more in Chapter 6)

  5. Common reverse proxies

    • Nginx, HAProxy, Caddy, Traefik
    • Cloud services (Cloudflare, AWS ALB)
    • Sentinel — a security-focused reverse proxy for the free web

  6. Sentinel’s philosophy (light touch)

    • Designed for people who want to protect their own corner of the web
    • Not about surveillance — about care
    • Fits the theme: understanding your infrastructure, not outsourcing blindly

Tone for this chapter

Welcoming but purposeful. The reverse proxy should feel like a helpful presence, not a barrier. Sentinel should be introduced as one example, not the hero of the story. The reader should understand why this layer exists and feel empowered to use it.

Bridge to Chapter 6

The doorman checks who comes in — but what about eavesdroppers? What about someone listening to the conversation? That’s where encryption matters. Time to talk about HTTPS.

Status: Work in progress