Expires directive in Nginx - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the expires directive in nginx?

The expires directive sets the caching time for responses, telling browsers how long to keep files before requesting them again.

beginner

How do you set a file to expire 1 hour after it is served using the expires directive?

Use expires 1h; inside the location or server block to tell browsers to cache the file for 1 hour.

intermediate

What does expires max; do in nginx?

It sets the cache expiration to a very long time (about 10 years), effectively telling browsers to keep the file indefinitely.

intermediate

How does the expires directive affect HTTP headers?

It modifies the Expires and Cache-Control headers to control browser caching behavior.

advanced

Can the expires directive use negative values? What happens if you use expires -1;?

Yes, negative values are allowed. expires -1; tells browsers not to cache the response and to revalidate it every time.

What does expires 30d; mean in an nginx config?

A Expire the file immediately

B Cache the file for 30 days

C Cache the file for 30 minutes

D Disable caching

expires 30d; tells browsers to cache the file for 30 days before requesting it again.

Which HTTP headers does the expires directive modify?

A User-Agent and Referer

B Content-Type and Content-Length

C Authorization and Cookie

D Expires and Cache-Control

The expires directive sets the Expires and Cache-Control headers to control caching.

What happens if you set expires off; in nginx?

A Caches files forever

B Sets cache to 1 hour

C Disables setting the Expires header

D Causes an error

expires off; disables adding the Expires header, so caching is not controlled by nginx.

How would you tell nginx to set caching to 10 minutes?

A expires 10m;

B expires 10h;

C expires 10s;

D expires 10d;

expires 10m; sets the cache time to 10 minutes.

What is the effect of expires -1; in nginx?

A Prevents caching and forces revalidation

B Caches for 1 second

C Caches forever

D Caches for 1 minute

expires -1; tells browsers not to cache and to check with the server every time.

Explain how the expires directive controls browser caching in nginx.

Think about how browsers know when to ask for a new file.

Describe a scenario where you would use expires max; and why.

Consider files that don’t change often and can be cached for a long time.

Practice

1. What is the main purpose of the expires directive in an nginx configuration?

easy

A. To specify the file upload size limit

B. To control how long browsers cache files before requesting them again

C. To limit the number of simultaneous connections

D. To set the server's time zone

Solution

1. Step 1: Understand the role of expires in nginx

   The expires directive tells browsers how long to keep files cached before checking for updates.

2. Step 2: Compare options with this function

   Only To control how long browsers cache files before requesting them again matches this purpose; others relate to different server settings.

3. Final Answer:

   To control how long browsers cache files before requesting them again -> Option B

4. Quick Check:

   Expires directive = browser cache time [OK]

Hint: Expires controls browser cache duration for files [OK]

Common Mistakes:

• Confusing expires with server timezone settings
• Thinking expires limits connections
• Mixing expires with upload size limits

2. Which of the following is the correct syntax to set the expires directive to 1 day in nginx?

easy

A. expires = 1 day;

B. expires 1 day

C. expires 24hours;

D. expires 1d;

Solution

1. Step 1: Recall nginx expires syntax

   The correct syntax uses a time value followed by a semicolon, e.g., expires 1d; for one day.

2. Step 2: Check each option for syntax correctness

   expires = 1 day; uses invalid '=' and full word 'day'; expires 1 day lacks semicolon; expires 24hours; uses invalid time unit '24hours'. Only B matches correct syntax: expires 1d;.

3. Final Answer:

   expires 1d; -> Option D

4. Quick Check:

   Correct syntax ends with semicolon and uses short time unit [OK]

Hint: Use short time units with semicolon, like 'expires 1d;' [OK]

Common Mistakes:

• Omitting semicolon at the end
• Using spaces in time value
• Writing full words like 'day' instead of 'd'

3. Given this nginx config snippet:

location ~* \.(jpg|jpeg|png)$ {
  expires 30d;
}

What will the browser do when accessing a PNG file?

medium

A. Cache the PNG file for 30 seconds

B. Never cache the PNG file

C. Cache the PNG file for 30 days before re-requesting

D. Immediately re-request the PNG file every time

Solution

1. Step 1: Analyze the regex and expires directive

   The location matches .jpg, .jpeg, and .png files and sets expires 30d;, meaning 30 days caching.

2. Step 2: Understand browser caching behavior

   Browsers will keep the PNG file cached for 30 days before checking for updates.

3. Final Answer:

   Cache the PNG file for 30 days before re-requesting -> Option C

4. Quick Check:

   Expires 30d means 30 days cache [OK]

Hint: Regex matches file types; expires sets cache time [OK]

Common Mistakes:

• Confusing days with seconds
• Ignoring regex file matching
• Assuming no caching without explicit 'no-cache'

4. Identify the error in this nginx config:

location /static/ {
  expires 10days;
}

medium

A. The time unit '10days' is invalid; should be '10d'

B. Missing semicolon after expires directive

C. Location block syntax is incorrect

D. Expires directive cannot be used inside location

Solution

1. Step 1: Check the expires time unit

   The correct time unit uses short forms like 'd' for days. '10days' is invalid syntax.

2. Step 2: Verify other syntax elements

   Semicolon is present, location syntax is correct, and expires can be used inside location.

3. Final Answer:

   The time unit '10days' is invalid; should be '10d' -> Option A

4. Quick Check:

   Use short time units like 'd' not full words [OK]

Hint: Use short units like 'd' for days, not full words [OK]

Common Mistakes:

• Writing full words for time units
• Forgetting semicolon (not the case here)
• Thinking expires can't be in location block

5. You want to set caching so that CSS files are cached for 7 days, but HTML files are never cached. Which nginx config snippet achieves this?

hard

A. location ~* \.css$ { expires 7d; } location ~* \.html$ { expires -1; }

B. location ~* \.css$ { expires 7d; } location ~* \.html$ { expires 0; }

C. location ~* \.css$ { expires 7d; } location ~* \.html$ { expires off; }

D. location ~* \.css$ { expires 7d; } location ~* \.html$ { expires never; }

Solution

1. Step 1: Recall how to disable caching in nginx

   Setting expires -1; disables caching (forces no cache) for files.

2. Step 2: Check each option for correct disables and enables

   location ~* \.css$ { expires 7d; } location ~* \.html$ { expires -1; } uses expires 7d; for CSS and expires -1; for HTML, which is correct. Others use invalid or incorrect values.

3. Final Answer:

   location ~* \.css$ { expires 7d; } location ~* \.html$ { expires -1; } -> Option A

4. Quick Check:

   Use 'expires -1;' to disable caching [OK]

Hint: Use 'expires -1;' to disable caching for files [OK]

Common Mistakes:

• Using 'expires off;' which is invalid
• Using 'expires 0;' which sets immediate expiry but not no-cache
• Using 'expires never;' which is not valid syntax