CloudFront Caching Overview

CloudFront is a content delivery network (CDN) service that optimizes the delivery of web content and applications by caching content in edge locations closer to users. Efficient caching strategies can significantly reduce the load on the origin server and improve content delivery speed. Here's a detailed breakdown of CloudFront caching mechanisms:

Headers

• HTTP requests include headers that can significantly impact caching behavior.
• CloudFront allows three configurations for handling headers:
  1. Forward all headers to the origin: This disables caching because each request is considered unique.
  2. Whitelist headers: Only selected headers are forwarded, allowing for efficient caching based on the values of these headers.
  3. No header forwarding: Maximizes caching efficiency as requests are not differentiated based on headers.
• The choice among these depends on application-specific needs. For example, applications that don't rely on headers for content delivery can benefit from not forwarding headers to improve caching.

Cookies

• Cookies are treated as a specific type of header with key-value pairs.
• CloudFront offers three options for cookie forwarding:
  1. No cookies: Ignores cookies for caching, not forwarding them to the origin.
  2. Whitelist cookies: Only forwards specified cookies, allowing caching decisions based on these.
  3. All cookies: Forwards all cookies, reducing caching efficiency but necessary if the application relies heavily on cookies.

Query String Parameters

• Query strings in URLs can also affect caching.
• Similar to headers and cookies, CloudFront allows for not processing query strings, whitelisting specific parameters, or forwarding all, impacting caching based on the application's reliance on these parameters.

TTL (Time to Live)

• CloudFront caching behavior is significantly influenced by TTL settings, which determine how long content is cached before being refreshed from the origin.
• TTL can be controlled via:
  1. Cache Control Header: Allows the origin server to specify TTL.
  2. Expires Header: An older method for specifying TTL.
  3. Custom TTL Settings: CloudFront allows setting minimum, maximum, and default TTL values, providing flexibility in cache control regardless of origin server headers.

The concepts of "Origin Headers" and "Cache Behavior" in Amazon CloudFront pertain to how CloudFront handles HTTP headers when interacting with the origin server and managing the cache. Understanding the differences between these two is crucial for effectively configuring CloudFront to serve content in the most efficient manner possible.

Origin Custom Headers

• Definition: Origin Custom Headers are specific headers that you configure CloudFront to add to every request that it forwards to your origin server. These headers are constant for all requests and do not vary based on the incoming request headers from the client.
• Purpose: The primary purpose of Origin Custom Headers is to provide additional information to the origin server that can be used for various reasons, such as identifying requests coming from CloudFront, implementing security policies, or customizing responses at the origin.
• Impact on Caching: Origin Custom Headers themselves do not directly influence CloudFront's caching behavior. The cache does not consider these custom headers when determining whether to serve a response from the cache or fetch a new one from the origin.