Media storage and CDN in HLD - Architecture Diagram

System Overview - Media storage and CDN

This system stores media files like images and videos and delivers them quickly to users worldwide. It uses a Content Delivery Network (CDN) to cache media close to users, reducing load times and server strain.

Architecture Diagram

CDN Edge Server

↓

Load Balancer

↓

Media Storage Service

↓

Object Storage

Components

User

client

Requests media content like images or videos

CDN Edge Server

cdn

Caches media content close to users to reduce latency and offload origin servers

Load Balancer

load_balancer

Distributes incoming media requests evenly across media storage service instances

Media Storage Service

service

Handles media requests, fetches media from object storage if not cached

Object Storage

storage

Stores original media files reliably and durably

Request Flow - 7 Hops

User → CDN Edge Server

CDN Edge Server → Cache (internal)

CDN Edge Server → Load Balancer

Load Balancer → Media Storage Service

Media Storage Service → Object Storage

Media Storage Service → CDN Edge Server

CDN Edge Server → User

Failure Scenario

Component Fails:CDN Edge Server

Impact:Users experience slower media delivery as requests bypass CDN cache and go directly to origin servers, increasing latency and load.

Mitigation:Traffic reroutes to other CDN edge servers or directly to load balancer; origin servers scale to handle increased load; CDN provider ensures multiple edge locations for redundancy.

Architecture Quiz - 3 Questions

Which component first checks if the media file is cached?

A Load Balancer

B Media Storage Service

C CDN Edge Server

D Object Storage

Design Principle

This design uses a CDN to cache media close to users, reducing latency and origin load. The load balancer distributes requests to scalable media service instances. Object storage holds original files reliably. Caching ensures fast repeated access, and failure handling ensures availability and performance.

Practice

1. What is the main purpose of a Content Delivery Network (CDN) in media storage systems?

easy

A. To store original media files permanently

B. To cache media files closer to users for faster access

C. To compress media files before storage

D. To encrypt media files for security

Solution

1. Step 1: Understand CDN role

   A CDN stores copies of media files in servers near users to reduce latency.

2. Step 2: Differentiate storage vs delivery

   Media storage holds original files; CDN speeds up delivery by caching.

3. Final Answer:

   To cache media files closer to users for faster access -> Option B

4. Quick Check:

   CDN = cache near users [OK]

Hint: CDN = cache near users for speed [OK]

Common Mistakes:

• Confusing CDN with permanent storage
• Thinking CDN compresses files
• Assuming CDN encrypts files

2. Which of the following is the correct sequence for serving media using storage and CDN?

easy

A. User requests -> CDN cache -> Origin storage if cache miss

B. User requests -> Origin storage -> CDN cache

C. CDN cache -> User requests -> Origin storage

D. Origin storage -> CDN cache -> User requests

Solution

1. Step 1: Understand request flow

   User first hits CDN cache to get media quickly.

2. Step 2: Handle cache miss

   If CDN cache misses, it fetches from origin storage and caches it.

3. Final Answer:

   User requests -> CDN cache -> Origin storage if cache miss -> Option A

4. Quick Check:

   Request flow = User -> CDN -> Storage [OK]

Hint: Requests hit CDN first, then storage if needed [OK]

Common Mistakes:

• Thinking origin storage serves user directly every time
• Reversing CDN and storage order
• Ignoring cache miss step

3. Consider a system where media files are stored in cloud storage and served via CDN. If the CDN cache TTL (time-to-live) is set to 1 hour, what happens when a media file is updated in storage immediately after a user requests it?

medium

A. User gets the updated file immediately from CDN

B. CDN automatically invalidates cache and fetches new file

C. User gets the old cached file from CDN until TTL expires

D. User request fails until cache refresh

Solution

1. Step 1: Understand CDN TTL effect

   TTL controls how long CDN keeps cached copy before checking origin.

2. Step 2: Effect of update during TTL

   Until TTL expires, CDN serves cached old file despite origin update.

3. Final Answer:

   User gets the old cached file from CDN until TTL expires -> Option C

4. Quick Check:

   Cache TTL = old file served until expiry [OK]

Hint: Cache TTL controls update delay [OK]

Common Mistakes:

• Assuming CDN always fetches fresh file immediately
• Thinking cache invalidates automatically on update
• Believing user request fails on stale cache

4. A developer implemented a media delivery system using CDN and storage but users report slow media loading. Which of the following is the most likely cause?

medium

A. CDN is caching files for too long

B. Media files are too small to benefit from CDN

C. Storage is located in the same region as users

D. CDN cache miss due to incorrect cache headers

Solution

1. Step 1: Analyze slow loading cause

   Slow loading often happens if CDN cache misses and fetches from origin repeatedly.

2. Step 2: Identify cache header role

   Incorrect or missing cache headers prevent CDN from caching files properly.

3. Final Answer:

   CDN cache miss due to incorrect cache headers -> Option D

4. Quick Check:

   Cache headers control CDN caching [OK]

Hint: Check cache headers if CDN misses often [OK]

Common Mistakes:

• Assuming small files don't benefit from CDN
• Thinking storage location alone causes slowness
• Believing long cache time causes slow loading

5. You are designing a global media storage system with CDN for a video streaming service. Which combination best improves scalability and user experience?

hard

A. Store media in a single central region and use CDN with regional edge caches

B. Store media in multiple regions without CDN to reduce latency

C. Use CDN only without origin storage to reduce costs

D. Store media locally on user devices to avoid network delays

Solution

1. Step 1: Consider storage and CDN roles

   Central storage simplifies management; CDN edge caches bring content close to users.

2. Step 2: Evaluate options for scalability and latency

   Multiple regions without CDN adds complexity; CDN without origin lacks source; local storage is impractical.

3. Final Answer:

   Store media in a single central region and use CDN with regional edge caches -> Option A

4. Quick Check:

   Central storage + CDN edges = scalable & fast [OK]

Hint: Central storage + CDN edges = best scalability [OK]

Common Mistakes:

• Ignoring CDN benefits by using multi-region storage only
• Thinking CDN can replace origin storage
• Assuming local user storage is feasible