Chapter 1 of AEM Learning Series — Understanding the core architecture used in every production AEM setup.

These 3 layers work together to deliver fast, secure, and scalable websites.

✍️ 1. AUTHOR Instance

What happens on Author?

• Drag & drop page building

• Upload images/videos to DAM

• Preview content before publishing

• Run workflows (review → approve → publish)

• Developers deploy code here first

Think of Author as the content factory 🏭

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🌐 2. PUBLISH Instance

What happens on Publish?

• Serves final HTML pages

• Contains only activated content

• No editing interface

• Multiple instances used for scaling

Publishing Flow

Author writes page → Clicks Publish → Replicates to Publish → Users see it

Think of Publish as the live website servers.

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⚡ 3. DISPATCHER (Most Important Layer)

How Dispatcher Works

Dispatcher’s 3 Superpowers

1️⃣ Caching → Stores rendered HTML
2️⃣ Security → Blocks malicious URLs
3️⃣ Load Balancing → Distributes traffic

👉 Dispatcher is NOT part of AEM — it runs on Apache/IIS.

🔄 Real-World Flow Example

Imagine Coca-Cola launches a Summer Sale Page:

1. Author creates page on Author

2. Clicks Publish

3. Content replicates to Publish

4. User visits website

5. Dispatcher checks cache

6. First user → page generated & cached

7. Next 10,000 users → cached version ⚡

This is how AEM handles massive traffic.

🏭 Production Setup (Enterprise Scale)

                         ┌──────────┐
                         │  AUTHOR  │
                         └────┬─────┘
                              │ Replication
           ┌──────────┬──────────┬──────────┐
           ▼          ▼          ▼
          PUBLISH1   PUBLISH2   PUBLISH3
               │          │          │
          DISPATCHER1 DISPATCHER2 DISPATCHER3
                    └──────┬──────┘
                           ▼
                     LOAD BALANCER
                           ▼
                        Users

Large enterprises run multiple publish + dispatcher nodes for high availability.

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🧾 Key Things to Remember

• Author → Content creation (private)

• Publish → Live website (public)

• Dispatcher → Cache + Security layer

• Content flows Author → Publish

• Users NEVER access Author directly

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🎯 AEM Interview Questions (30 Q&A)

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🟢 Section A — Basics

Q1. What is AEM?
AEM is an enterprise CMS used to create, manage and deliver digital experiences.

Q2. AEM technology stack?
OSGi • JCR • Sling • HTL • Java

Q3. Three tiers of AEM?
Author • Publish • Dispatcher

Q4. Author instance?
Content creation environment (port 4502).

Q5. Publish instance?
Live website server (port 4503).

Q6. Dispatcher?
Apache module for caching, security, load balancing.

Q7. Default ports?
Author → 4502 | Publish → 4503

Q8. Author users?
Authors, marketers, developers.

Q9. Publish users?
Website visitors.

Q10. AEM language?
Java.

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🔵 Section B — Replication

Q11. Replication?
Author → Publish content transfer.

Q12. Activation vs Deactivation?
Publish vs Unpublish.

Q13. Reverse replication?
Publish → Author data flow.

Q14. Replication agent?
Configuration controlling replication.

Q15. Publish → Author publishing?
Not directly (only reverse replication).

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🟣 Section C — Dispatcher

Q16. Dispatcher functions?
Caching • Security • Load balancing.

Q17. Where installed?
Apache HTTP / IIS server.

Q18. Cache miss?
Request sent to Publish → cached.

Q19. Cache invalidation?
Flush agent clears cache.

Q20. Personalized content caching?
No — use AJAX/client-side.

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🟠 Section D — Production

Q21. Author instances in prod?
Usually 1 (or primary + standby).

Q22. Publish instances?
3–10+ depending on traffic.

Q23. In front of Dispatcher?
Load balancer or CDN.

Q24. Hosting types?
On-Prem • AMS • Cloud Service.

Q25. Full request flow?
Browser → LB → Dispatcher → Publish → Response.

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🔴 Section E — Scenarios

Q26. Users see old content?
Check dispatcher/CDN cache or replication.

Q27. Author down — website works?
Yes.

Q28. Publish down — website works?
Cached pages still load.

Q29. Wrong content published?
Republish or deactivate.

Q30. Why Author behind VPN?
Security & protection.

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🎉 Summary

If you understand this architecture, you understand the foundation of AEM.

Everything else in AEM builds on this.