Generate Static Content On Demand
Understanding SCD_ON_DEMAND behavior, four applied patches, time measurements, security implications, and when to use it.
Static Content On Demand
Default Magento Behavior in Production Mode
Production Mode Static Content Handling
Default Production Behavior
By default, production mode disables generating any static content files.
Why?
- Speed: Uploading content from the website is faster
- Efficiency: Magento doesn't have to look for new content
- Security: Static files are read-only (pre-generated)
The Problem
This default behavior prevents on-demand deployment of static content. You cannot generate static files dynamically in production mode without special configuration.
Why SCD_ON_DEMAND Mode Was Added
The "Magento Way" Solution
Purpose of SCD_ON_DEMAND
As with everything "Magento," there's a way around the production mode restriction!
- Development speed: Skip SCD during build and deploy
- Flexibility: Generate static content as needed on first request
- Rapid deployment: Faster deployment cycles during development
- Dynamic generation: Support new themes/locales without redeployment
How It Works
When SCD_ON_DEMAND is enabled, Magento generates static content files dynamically on the first request for each file, then caches them for subsequent requests.
How Magento Behaves with SCD_ON_DEMAND
Configuration and Setup
Step 1: Enable in .magento.env.yaml
stage:
deploy:
SCD_ON_DEMAND: trueStep 2: Deploy Scripts Update env.php
When deploying in on-demand mode, the deploy scripts add this to app/etc/env.php:
'static_content_on_demand_in_production' => 1Critical Detail
Even more important: patches are applied to Magento so it understands this flag. The functionality is somewhat present in core, but patches ensure full support.
Patches Applied for SCD_ON_DEMAND
Four Critical Patches
1. configure_scd_on_demand
Purpose
If in production mode AND static_content_on_demand_in_production is configured, then the asset can be created.
Additional Functionality
- Allows newly generated files to be minified
- Enables dynamic asset creation in production
- Core logic for on-demand generation
2. respect_minification_override
Purpose
Adds OR logic for minification decisions:
- IF production SCD is enabled OR
- IF force_html_minification is enabled
- THEN the file is minified
This ensures minification works correctly with on-demand generation.
3. unlock_locale_editing
The Problem
When in production mode, the Locale is locked in Store → Configuration → General → Locale Options to the locales for which themes have been generated.
The Solution
This patch unlocks the locale setting so you can generate static content for any locale, not just pre-generated ones.
4. trim_static_content
Purpose
Removes /static/version[NUMBER] from the $_GET['resource'].
Why?
The version number in static URLs can interfere with on-demand generation. This patch normalizes the resource path for proper dynamic generation.
When to Use SCD_ON_DEMAND
Appropriate Use Cases
Good Use Cases
This should only be done in the development (pre-release) phase of a project.
- Development environment: Rapid iteration and testing
- Integration environment: Frequent deployments
- Pre-release testing: Testing new themes or locales
- Demo environments: Quick setup without full SCD
NOT for Production
SCD_ON_DEMAND should NOT be used in production!
Reasons Why:
- Inconsistencies: No guarantee files will be identical to intended output
- Performance: First requests are very slow (9+ seconds)
- Security risk: Static files are no longer read-only, opening attack vectors
- Unpredictable behavior: Different users might trigger different generation patterns
- Resource usage: Generates files on production servers, consuming resources
Security Considerations
Read-Only vs Writable Static Files
Pre-Generated SCD (Secure)
- Files are read-only
- Cannot be modified after generation
- Protects against injection attacks
- Consistent across all requests
SCD_ON_DEMAND (Less Secure)
- Files are writable
- Can be modified dynamically
- Potential attack vector
- Risk of inconsistent generation
Security Risk
While the risk is small, there is some possibility of attack as static files are no longer read-only with SCD_ON_DEMAND. Attackers could potentially inject malicious code into dynamically generated static files.
Time Measurements
Performance Impact
| File | First Load (Generation) | Subsequent Loads (Cached) |
|---|---|---|
| styles-m.css | 9.4 seconds | < 300 ms |
| styles-l.css | 4.54 seconds | < 300 ms |
Key Insights
- First load: VERY slow (4-9+ seconds per file)
- Subsequent loads: Fast (< 300ms, served from cache)
- User impact: First visitors experience very slow page loads
- Production impact: Unacceptable for production environments
Why This Matters
These generation times occur on the first request for each static file. In production, this means the first users to visit your site (or any new page) will experience extremely slow load times while static content is generated.
How It Works: Request Flow
On-Demand Generation Process
Step-by-Step Flow
- Request arrives: Browser requests static file (e.g., styles-m.css)
- File check: Magento checks if file exists in pub/static
- Not found: File doesn't exist yet
- Generate: Magento generates the file dynamically (SLOW - 4-9+ seconds)
- Cache: Generated file is saved to pub/static
- Serve: File is served to browser
- Subsequent requests: File exists, served quickly (< 300ms)
Practical Experience Exercise
Testing SCD_ON_DEMAND
Step 1: Enable SCD_ON_DEMAND
Add to .magento.env.yaml:
stage:
deploy:
SCD_ON_DEMAND: trueStep 2: Deploy Your Development Project
git add .magento.env.yaml
git commit -m "Enable SCD_ON_DEMAND for testing"
git push origin developmentStep 3: Switch Locale for Frontend
- Navigate to Store → Configuration → General → Locale Options
- Change locale (e.g., from en_US to fr_FR)
- Save configuration
- Clear cache
Step 4: Observe Behavior
- First page load: Notice very slow load time (9+ seconds)
- Check browser network tab: See static files taking 4-9 seconds each
- Refresh page: Notice much faster load (< 300ms per file)
- Check pub/static: See dynamically generated files
Expected Observations
- Locale can be changed without redeployment
- Static content generates automatically on first request
- Subsequent requests are fast (files cached)
- No build or deploy time spent on SCD
SCD_ON_DEMAND Configuration
Complete Configuration Example
Optimal Development Setup
# .magento.env.yaml
stage:
global:
MIN_LOGGING_LEVEL: debug
build:
SKIP_SCD: true # Skip in build
deploy:
SCD_ON_DEMAND: true # Generate on demand
SKIP_SCD: true # Skip in deploy
post_deploy:
WARM_UP_PAGES:
- "/"
- "/customer/account/login"Configuration Notes
- SKIP_SCD: true in build and deploy prevents traditional SCD
- SCD_ON_DEMAND: true enables on-demand generation
- WARM_UP_PAGES: Optional, pre-generates content for specified pages
Comparison: Traditional SCD vs SCD_ON_DEMAND
| Aspect | Traditional SCD | SCD_ON_DEMAND |
|---|---|---|
| When Generated | During build or deploy | On first request |
| Build Time | Long (generates all content) | Fast (nothing generated) |
| Deploy Time | Long if SCD in deploy | Fast (nothing generated) |
| First Page Load | Fast (content pre-generated) | Very slow (4-9+ seconds per file) |
| Subsequent Loads | Fast | Fast (< 300ms) |
| File Security | Read-only (secure) | Writable (security risk) |
| Consistency | Guaranteed identical | Potential inconsistencies |
| Locale Flexibility | Locked to pre-generated | Any locale on demand |
| Production Use | Recommended | NOT recommended |
| Development Use | Optional | Ideal for rapid iteration |
Exam Tips
Key Points to Remember
- Default production: Disables static content generation
- Why added: Development speed, skip SCD, generate as needed
- Configuration: SCD_ON_DEMAND: true in .magento.env.yaml
- env.php flag: static_content_on_demand_in_production
- Four patches: configure_scd_on_demand, respect_minification_override, unlock_locale_editing, trim_static_content
- configure_scd_on_demand: Enables asset creation in production, allows minification
- unlock_locale_editing: Unlocks locale selection in Store Configuration
- trim_static_content: Removes /static/version[NUMBER] from URL
- When to use: Development/pre-release ONLY
- NOT for production: Inconsistencies, slow first load, security risk
- Time impact: 4-9+ seconds first load, < 300ms cached
- Security: Files writable (attack vector), not read-only
- Locale flexibility: Can generate for any locale on demand
