HTTP Response Header Invalidation for Cache Staleness
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Solution Overview
Problem
Current mechanisms for invalidating stale cache responses in HTTP requests, such as timestamp-based and out-of-band invalidation, are inefficient and pose security risks, especially when caching occurs behind a firewall, and are limited by their requirement for extra overhead and specific ports, while ESI inline invalidation only works with HTML content.
Innovation Solution
A response header invalidation mechanism that embeds an invalidation directive within the HTTP response header, allowing for efficient and secure invalidation of cached content without additional port overhead or security risks, and functioning with any content type, not just HTML.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If out-of-band invalidation is used to invalidate cached content, then invalidation can be performed, but extra overhead is required to establish a separate connection over a special invalidation port and security risks arise from poking holes through firewalls
Solution Approach 1:
The patent combines the invalidation function with the existing HTTP response mechanism by embedding invalidation directives in response headers. This merges two separate functions (content delivery and invalidation signaling) into a single HTTP response, eliminating the need for separate invalidation connections and ports, thereby reducing connection overhead and firewall complexity while maintaining reliable invalidation capability
Solution Approach 2:
The HTTP response header is given multi-functionality by embedding both content metadata and invalidation directives within the same header structure. This allows the existing HTTP infrastructure to serve dual purposes: delivering content information and simultaneously providing invalidation signals, thus eliminating the need for dedicated invalidation ports and reducing overall system complexity
2Reliability
If timestamp-based invalidation is used, then cached responses can be marked as invalid, but users have difficulty setting the timestamp value a-priori as they do not know how long a cached entry will remain valid
Solution Approach 1:
The origin server automatically generates and embeds the invalidation directive in the response header based on its own knowledge of content validity. This eliminates the need for users or cache systems to manually configure timestamp values, as the invalidation information is self-provided by the content authority (origin server) within the HTTP response itself, making the system easier to operate while maintaining reliable stale content detection
3Reliability
If ESI inline invalidation is used, then invalidation can be embedded in the response body, but it only works when the response body contains an HTML document since ESI tags can only be embedded in HTML
Solution Approach 1:
The patent extends the invalidation mechanism to work with any content type by placing invalidation directives in the HTTP response header rather than embedding them in the response body. Since HTTP headers are universally supported regardless of content type (HTML, XML, JSON, binary, etc.), this approach makes the invalidation mechanism adaptable to all content types, eliminating the limitation of ESI tags that only work with HTML documents
4Reliability
If out-of-band invalidation requests are sent, then cached content can be invalidated, but they can have difficulty getting scheduled if normal HTTP request activity has reached a capacity limit
Solution Approach 1:
The patent merges the invalidation signal with the existing HTTP response traffic by embedding invalidation directives in response headers. This allows invalidation to be delivered piggybacking on normal HTTP responses that are already being sent to clients, eliminating the need for separate invalidation requests that would compete for scheduling resources. Consequently, invalidation delivery becomes more reliable and timely without adding scheduling delays
Data Source
AI summary
Systems, methods, and other embodiments associated with content invalidation are described. One example method includes parsing a response to identify an invalidation directive. Then if identified, invalidating cached content from a cache memory that corresponds to the content identified by an invalidation directive.