Media storage and CDN in HLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the primary storage type for media files.

HLD

media_storage = [1]

Drag options to blanks, or click blank then click option'

AObjectStorage

BMessageQueue

CInMemoryCache

DRelationalDatabase

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing relational databases which are not optimized for large binary files.

Using in-memory cache which is volatile and limited in size.

Object storage is ideal for storing large media files because it is scalable and optimized for unstructured data.

2fill in blank

medium

Complete the code to define the CDN component responsible for caching media content.

HLD

cdn_cache = [1]

Drag options to blanks, or click blank then click option'

AEdgeServer

BLoadBalancer

CDatabaseReplica

DMessageBroker

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing load balancers with caching servers.

Using database replicas which do not serve cached media content.

Edge servers in a CDN cache media content close to users to reduce latency and improve delivery speed.

3fill in blank

hard

Fix the error in the request flow to ensure media requests are routed to the nearest CDN node.

HLD

user_request -> [1] -> origin_server

Drag options to blanks, or click blank then click option'

ALoadBalancer

BMessageQueue

CEdgeServer

DDatabase

Attempts:

3 left

💡 Hint

Common Mistakes

Routing requests directly to the origin server causing higher latency.

Using load balancers which do not cache content.

Requests should first go to the nearest edge server (CDN node) to serve cached content before reaching the origin server.

4fill in blank

hard

Fill both blanks to complete the media upload flow with caching and storage.

HLD

upload_request -> [1] -> [2] -> confirmation

Drag options to blanks, or click blank then click option'

AOriginServer

BEdgeServer

CObjectStorage

DLoadBalancer

Attempts:

3 left

💡 Hint

Common Mistakes

Sending uploads directly to edge servers which are for caching, not storage.

Skipping load balancer causing uneven request distribution.

Uploads first go through a load balancer to distribute requests, then are stored in object storage for durability.

5fill in blank

hard

Fill all three blanks to define a dictionary mapping media types to their CDN cache policies.

HLD

cache_policies = {"image": [1], "video": [2], "audio": [3]

Drag options to blanks, or click blank then click option'

A"short_ttl"

B"long_ttl"

C"medium_ttl"

D"no_cache"

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning no_cache to all media types causing poor performance.

Using short TTL for videos leading to frequent cache misses.

Images often have medium TTL, videos have long TTL due to size and popularity, and audio has short TTL for freshness.

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