CloudFront cache behaviors are rules that define how Amazon CloudFront handles requests for your content. They determine which origin receives requests, how content is cached, and what settings apply to specific URL patterns.
Each CloudFront distribution has a default cache behavior that applies t…CloudFront cache behaviors are rules that define how Amazon CloudFront handles requests for your content. They determine which origin receives requests, how content is cached, and what settings apply to specific URL patterns.
Each CloudFront distribution has a default cache behavior that applies to all requests not matching other patterns. You can create additional cache behaviors with path patterns like /images/* or /api/* to customize handling for different content types.
Key components of cache behaviors include:
**Path Pattern**: Specifies which requests the behavior applies to. The default behavior uses * to match everything. Custom behaviors use specific patterns that take precedence over the default.
**Origin Settings**: Determines which origin server CloudFront forwards requests to when cache misses occur. You can route different paths to different origins.
**Viewer Protocol Policy**: Controls whether viewers can use HTTP, HTTPS, or if HTTP requests should redirect to HTTPS.
**Cache Policy**: Defines TTL values (minimum, maximum, and default) and which headers, cookies, and query strings are included in the cache key.
**Origin Request Policy**: Specifies which values CloudFront includes when forwarding requests to your origin.
**Allowed HTTP Methods**: Determines which methods (GET, HEAD, PUT, POST, PATCH, DELETE, OPTIONS) CloudFront processes.
**Compress Objects**: Enables automatic compression of certain file types to reduce transfer sizes.
**Lambda@Edge Functions**: Allows you to associate serverless functions that execute at edge locations for request/response manipulation.
Cache behaviors are evaluated in order, with the first matching path pattern being applied. This enables sophisticated content delivery strategies where static assets have long cache durations while dynamic API responses bypass caching entirely. Understanding cache behaviors is essential for optimizing performance, reducing origin load, and controlling costs in your CloudFront distributions.
CloudFront cache behaviors are essential for controlling how your CDN handles different types of content. They allow you to customize caching rules, specify origin servers, and define how requests are processed based on URL patterns. For the AWS SysOps Administrator Associate exam, understanding cache behaviors is critical because they directly impact application performance, cost optimization, and content delivery strategies.
What Are CloudFront Cache Behaviors?
Cache behaviors are rules that define how CloudFront processes requests for your content. Each CloudFront distribution has a default cache behavior and can have multiple additional cache behaviors that apply to specific path patterns.
Key components of cache behaviors include: - Path Pattern: URL patterns that determine which requests the behavior applies to (e.g., *.jpg, /api/*, /images/*) - Origin: The source server where CloudFront fetches content - Viewer Protocol Policy: HTTP/HTTPS settings for viewer connections - Cache Policy: Rules for what gets cached and for how long - Origin Request Policy: What headers, cookies, and query strings are forwarded to the origin - TTL Settings: Minimum, maximum, and default time-to-live values
How Cache Behaviors Work
When CloudFront receives a request, it evaluates cache behaviors in order of precedence:
1. CloudFront matches the request path against path patterns starting from the most specific 2. The first matching cache behavior is applied 3. If no path pattern matches, the default cache behavior is used 4. Based on the matched behavior, CloudFront determines caching rules, which origin to use, and how to process the request
Important Cache Behavior Settings:
Viewer Protocol Policy Options: - HTTP and HTTPS - Redirect HTTP to HTTPS - HTTPS Only
Cache Key Settings: - Headers included in cache key - Query strings included in cache key - Cookies included in cache key
Common Use Cases
1. Static vs Dynamic Content: Create separate behaviors for /static/* (long TTL) and /api/* (short TTL or no caching)
2. Multiple Origins: Route /images/* to an S3 bucket and /api/* to an Application Load Balancer
3. Security Requirements: Enforce HTTPS for sensitive paths while allowing HTTP for public content
4. Geographic Restrictions: Apply different restrictions based on content type
Exam Tips: Answering Questions on CloudFront Cache Behaviors
Tip 1: Remember that cache behaviors are evaluated in order - the most specific path pattern should be listed first. The default behavior (*) always processes requests that do not match any other pattern.
Tip 2: When a question mentions different caching requirements for different content types (images vs API responses), think cache behaviors with different path patterns and TTL settings.
Tip 3: For scenarios requiring content from multiple origins, recognize that each cache behavior can point to a different origin - this is how you route different URL paths to different backends.
Tip 4: If a question asks about reducing origin load or improving cache hit ratio, consider which headers, cookies, and query strings are included in the cache key. Fewer items in the cache key means better cache efficiency.
Tip 5: Questions about enforcing HTTPS are solved through the Viewer Protocol Policy setting within cache behaviors - choose 'Redirect HTTP to HTTPS' or 'HTTPS Only'.
Tip 6: When POST, PUT, or DELETE methods need to reach your origin, ensure the cache behavior allows these methods - the default is GET and HEAD only.
Tip 7: For questions about Lambda@Edge or CloudFront Functions, remember these are associated with specific cache behaviors and can run at different stages of the request/response cycle.
Tip 8: Origin Request Policy and Cache Policy are separate - Cache Policy controls what is cached, while Origin Request Policy controls what is forwarded to origin servers on cache misses.
Key Exam Scenarios to Watch For: - Optimizing cache hit ratios (minimize cache key components) - Routing requests to different origins based on path - Implementing HTTPS enforcement - Handling dynamic content that should not be cached - Passing specific headers or cookies to origins