Expiration-based caching in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is expiration-based caching in REST APIs?

Expiration-based caching is a technique where cached data is stored with a time limit. After this time expires, the cache is considered stale and must be refreshed from the server.

beginner

What HTTP header is commonly used to specify cache expiration time?

The Cache-Control header with directives like max-age is used to specify how long a response can be cached before it expires.

intermediate

How does the Expires header differ from Cache-Control: max-age?

Expires sets an absolute date/time when the cache expires, while Cache-Control: max-age sets a relative time in seconds from the response time.

beginner

Why is expiration-based caching useful in REST APIs?

It reduces server load and speeds up responses by reusing data for a set time, while ensuring data is refreshed regularly to stay up-to-date.

beginner

What happens when cached data expires in expiration-based caching?

When cached data expires, the client or proxy must request fresh data from the server to replace the stale cache.

Which HTTP header sets a relative expiration time for cached data?

A Cache-Control: max-age

B Expires

C Content-Type

D Authorization

Cache-Control: max-age sets the cache expiration time relative to the response time.

What does expiration-based caching help improve in REST APIs?

A Database schema design

B Security of data

C Response speed and server load

D User authentication

Expiration-based caching improves response speed and reduces server load by reusing cached data.

If a cached response has expired, what should happen next?

A Use the expired cache anyway

B Request fresh data from the server

C Delete the cache and do nothing

D Ignore the expiration and continue

Expired cache must be refreshed by requesting fresh data from the server.

Which header sets an absolute expiration date/time for cached data?

A Expires

B Cache-Control: max-age

C Content-Length

D Accept

Expires header specifies an absolute date/time when the cache expires.

What is a key benefit of using expiration-based caching?

A Prevents all caching

B Encrypts data for security

C Automatically deletes user data

D Ensures data is regularly updated while improving performance

Expiration-based caching balances performance with data freshness by updating data regularly.

Explain how expiration-based caching works in REST APIs and why it is important.

Think about how long cached data stays valid and what happens after.

Describe the difference between the HTTP headers Expires and Cache-Control: max-age.

One sets a fixed date, the other sets a time duration.

Practice

1. What does the Cache-Control: max-age header do in expiration-based caching?

easy

A. It deletes the cache immediately after the response.

B. It disables caching for the resource.

C. It sets how long the cached data is considered fresh.

D. It forces the client to always fetch new data.

Solution

1. Step 1: Understand the role of Cache-Control header

   The Cache-Control header controls caching behavior for HTTP responses.

2. Step 2: Identify the meaning of max-age directive

   The max-age directive specifies the time in seconds that the response is considered fresh and can be served from cache.

3. Final Answer:

   It sets how long the cached data is considered fresh. -> Option C

4. Quick Check:

   max-age = cache freshness duration [OK]

Hint: Remember max-age sets cache freshness time in seconds [OK]

Common Mistakes:

• Confusing max-age with disabling cache
• Thinking max-age deletes cache immediately
• Assuming max-age forces fresh fetch every time

2. Which of the following is the correct syntax to set a cache expiration of 300 seconds in an HTTP response header?

easy

A. Cache-Control: maxage: 300

B. Cache-Control: max-age=300

C. Cache-Control: expire=300

D. Cache-Control: timeout=300

Solution

1. Step 1: Recall correct Cache-Control syntax

   The Cache-Control header uses directives separated by commas, with max-age specified as max-age=seconds.

2. Step 2: Compare options to correct syntax

   Only Cache-Control: max-age=300 uses the correct format: max-age=300.

3. Final Answer:

   Cache-Control: max-age=300 -> Option B

4. Quick Check:

   Correct header syntax = max-age=seconds [OK]

Hint: Use equal sign (=) with max-age, no spaces [OK]

Common Mistakes:

• Using colon instead of equal sign
• Using incorrect directive names like expire or timeout
• Adding spaces inside the directive

3. Given this HTTP response header:
Cache-Control: max-age=10
What will happen if a client requests the same resource 5 seconds later?

medium

A. The client will use the cached response without contacting the server.

B. The client will ignore the cache and fetch new data from the server.

C. The client will receive a 404 error.

D. The client will refresh the cache but still use old data.

Solution

1. Step 1: Understand max-age meaning

   max-age=10 means the cached data is fresh for 10 seconds after the first fetch.

2. Step 2: Check time elapsed since caching

   5 seconds is less than 10 seconds, so cache is still fresh and valid.

3. Final Answer:

   The client will use the cached response without contacting the server. -> Option A

4. Quick Check:

   Elapsed time < max-age = use cache [OK]

Hint: If request time < max-age, cache is used [OK]

Common Mistakes:

• Assuming cache expires immediately
• Thinking client always fetches new data
• Confusing max-age with cache invalidation

4. You set Cache-Control: max-age=60 but clients still fetch new data every time. What is the likely mistake?

medium

A. The client does not support caching headers.

B. The max-age value should be in milliseconds, not seconds.

C. The resource URL is missing a file extension.

D. The server is sending no-cache header overriding max-age.

Solution

1. Step 1: Check for conflicting headers

   If the server sends a no-cache directive, it forces clients to revalidate or fetch fresh data despite max-age.

2. Step 2: Understand max-age units and client support

   max-age is in seconds, and most clients support caching headers, so these are unlikely causes.

3. Final Answer:

   The server is sending no-cache header overriding max-age. -> Option D

4. Quick Check:

   no-cache overrides max-age [OK]

Hint: Check for no-cache header overriding max-age [OK]

Common Mistakes:

• Confusing seconds with milliseconds for max-age
• Blaming client support without checking headers
• Assuming URL format affects caching

5. You want to cache API responses for 5 minutes but ensure clients always get fresh data after expiration. Which header setup is best?

hard

A. Cache-Control: max-age=300, must-revalidate

B. Cache-Control: max-age=300, no-store

C. Cache-Control: no-cache, max-age=300

D. Cache-Control: max-age=0, public

Solution

1. Step 1: Understand caching for 5 minutes

   max-age=300 sets cache freshness for 300 seconds (5 minutes).

2. Step 2: Ensure fresh data after expiration

   must-revalidate forces clients to check with server after max-age expires before using cached data.

3. Step 3: Evaluate other options

   no-store disables caching, no-cache forces revalidation every time, max-age=0 means no caching.

4. Final Answer:

   Cache-Control: max-age=300, must-revalidate -> Option A

5. Quick Check:

   max-age + must-revalidate = cache then fresh after expiry [OK]

Hint: Use must-revalidate with max-age for fresh data after expiry [OK]

Common Mistakes:

• Using no-store disables caching completely
• Using no-cache forces revalidation every request
• Setting max-age=0 disables caching