Public and assets folders in Ruby on Rails - Performance & Optimization

Performance: Public and assets folders

MEDIUM IMPACT

This concept affects page load speed by controlling how static files like images, stylesheets, and scripts are served to the browser.

Serving static images and stylesheets in a Rails app

Ruby on Rails

Use the assets folder with the Rails asset pipeline to fingerprint, compress, and cache static files before deployment.

Files are optimized and cached, reducing load size and speeding up repeat visits.

📈 Performance GainReduces file size by 30-70%, enables browser caching, and speeds up LCP.

Serving static images and stylesheets in a Rails app

Ruby on Rails

Place all images and CSS files directly in the public folder without fingerprinting or compression.

Files are served without caching benefits or compression, causing slower load times and larger downloads.

📉 Performance CostBlocks rendering longer due to uncompressed large files; no cache control increases repeated load times.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Unoptimized public folder files	0 (static files)	0	High due to large file size	[X] Bad
Optimized assets folder with fingerprinting	0 (static files)	0	Low due to compression and caching	[OK] Good

Rendering Pipeline

Static files from public or assets folders are requested by the browser, then served by the server or CDN. Optimized assets reduce time in network transfer and browser parsing.

→Network Transfer

→Style Calculation

→Paint

⚠️ BottleneckNetwork Transfer due to file size and caching strategy

Core Web Vital Affected

LCP

This concept affects page load speed by controlling how static files like images, stylesheets, and scripts are served to the browser.

Optimization Tips

1Always use the Rails asset pipeline to fingerprint and compress assets before deployment.

2Serve static files with proper cache-control headers to enable browser caching.

3Avoid placing large uncompressed files directly in the public folder to reduce load times.

Performance Quiz - 3 Questions

Why is fingerprinting assets in Rails important for performance?

A It reduces the number of files in the assets folder.

B It automatically compresses files on the server.

C It allows browsers to cache files effectively by changing filenames when content changes.

D It moves files from public to assets folder.

DevTools: Network

How to check: Open DevTools, go to Network tab, reload page, and inspect static file sizes and caching headers.

What to look for: Look for compressed file sizes (gzip or brotli), cache-control headers, and fast load times for assets.

Practice

1. What is the main purpose of the public folder in a Rails application?

easy

A. To store static files served directly without processing

B. To hold Ruby code files for controllers and models

C. To keep database migration files

D. To store files that Rails compiles before sending

Solution

1. Step 1: Understand the role of the public folder

   The public folder contains files like images, HTML, or JavaScript that Rails serves directly to the browser without any processing.

2. Step 2: Compare with other folders

   The assets folder is for files Rails processes (like compiling CSS or JavaScript), so it is not the public folder's role.

3. Final Answer:

   To store static files served directly without processing -> Option A

4. Quick Check:

   Public folder = static files served directly [OK]

Hint: Public folder serves files as-is, no processing needed [OK]

Common Mistakes:

• Confusing public with assets folder
• Thinking public holds Ruby code
• Assuming public processes files before serving

2. Which of the following is the correct path to place a CSS file that Rails will precompile and serve?

easy

A. app/public/stylesheets/style.css

B. public/assets/stylesheets/style.css

C. app/assets/stylesheets/style.css

D. config/assets/stylesheets/style.css

Solution

1. Step 1: Identify the standard assets folder for stylesheets

   Rails expects CSS files to be inside app/assets/stylesheets for precompilation and processing.

2. Step 2: Eliminate incorrect paths

   The public folder is for static files, not processed assets. The config folder does not hold assets.

3. Final Answer:

   app/assets/stylesheets/style.css -> Option C

4. Quick Check:

   CSS in assets/stylesheets = app/assets/stylesheets/style.css [OK]

Hint: Assets folder is inside app/, not public or config [OK]

Common Mistakes:

• Placing CSS directly in public folder
• Using wrong folder like config/assets
• Confusing assets with public folder paths

3. Given a file logo.png placed inside public/images, what URL path will serve this image in a Rails app?

medium

A. /assets/images/logo.png

B. /public/images/logo.png

C. /app/assets/images/logo.png

D. /images/logo.png

Solution

1. Step 1: Understand how public folder maps to URL

   Files inside public are served from the root URL path. So public/images/logo.png is accessible at /images/logo.png.

2. Step 2: Eliminate other options

   /assets/images/logo.png is for assets pipeline files, not public. /public/images/logo.png and /app/assets/images/logo.png are not valid URL paths.

3. Final Answer:

   /images/logo.png -> Option D

4. Quick Check:

   Public folder maps directly to root URL [OK]

Hint: Public folder files appear at root URL path [OK]

Common Mistakes:

• Using /assets prefix for public files
• Including 'public' in URL path
• Confusing assets and public URL paths

4. You placed a JavaScript file in app/assets/javascripts but it is not loading in your Rails app. What is a likely cause?

medium

A. You forgot to include the JavaScript pack or manifest in your layout

B. The file is missing from the public folder

C. JavaScript files must be placed in public/javascripts

D. Rails does not support JavaScript in assets folder

Solution

1. Step 1: Check how assets are loaded in Rails

   Files in app/assets/javascripts need to be referenced in your layout via a manifest or pack tag to load properly.

2. Step 2: Eliminate incorrect causes

   JavaScript files do not belong in public for processing. Rails fully supports JavaScript in assets folder.

3. Final Answer:

   You forgot to include the JavaScript pack or manifest in your layout -> Option A

4. Quick Check:

   Assets must be linked in layout to load [OK]

Hint: Always include asset manifests or packs in your layout [OK]

Common Mistakes:

• Expecting assets to load without linking in layout
• Placing JS files in wrong folders
• Thinking public folder is for processed assets

5. You want to add a favicon to your Rails app that loads instantly without asset pipeline processing. Where should you place the favicon file and how should you reference it in your HTML?

hard

A. Place in app/assets/images and use <%= favicon_link_tag 'favicon.ico' %>

B. Place in public folder root and use <link rel='shortcut icon' href='/favicon.ico'>

C. Place in app/assets/images and use <link rel='icon' href='/assets/favicon.ico'>

D. Place in public/images and use <%= image_tag 'favicon.ico' %>

Solution

1. Step 1: Choose folder for instant loading without processing

   Files in public are served directly, so placing favicon.ico in public root ensures instant loading.

2. Step 2: Reference favicon correctly in HTML

   Use a standard HTML <link> tag with href pointing to /favicon.ico for browsers to find it.

3. Final Answer:

   Place in public folder root and use <link rel='shortcut icon' href='/favicon.ico'> -> Option B

4. Quick Check:

   Favicon in public root + direct link = Place in public folder root and use <link rel='shortcut icon' href='/favicon.ico'> [OK]

Hint: Put favicon in public root and link with standard HTML tag [OK]

Common Mistakes:

• Placing favicon in assets and expecting instant load
• Using image_tag instead of link tag for favicon
• Referencing wrong URL path for favicon