Semantic CDN Caching for RAG Access-Controlled LLM Responses
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Solution Overview
Problem
RAG-based LLMs face challenges in ensuring access permission constraints are observed in a CDN-based front door, as different users may have varying access levels to external documents, and dynamic changes in permissions can violate DAC policies, impacting commercial feasibility.
Innovation Solution
Implement a CDN that caches LLM responses with document citations and user tags, verifying access permissions before providing cached responses and purging data based on DAC updates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a CDN caches LLM responses to reduce server load and latency, then response time and productivity improve, but access permission constraints may be violated and reliability deteriorates
Solution Approach 1:
The system performs preliminary actions by caching LLM responses along with associated metadata (user IDs, document citations, timestamps) before permission violations occur. When a request comes in, the system checks cached entries against current permission policies beforehand, preventing potential violations before they affect users.
Solution Approach 2:
The system implements feedback mechanisms by continuously monitoring permission changes and using this information to update or purge cached entries. When permission policies change, the system receives feedback about the new constraints and adjusts the cache accordingly, ensuring ongoing compliance without manual intervention.
Solution Approach 3:
The CDN acts as an intermediary between users and the LLM service. It introduces a layer of mediation that handles permission checking and cache management, allowing the system to maintain both fast responses and strict permission compliance by filtering and validating requests before they reach the LLM.
2Reliability
If the system verifies access permissions for every cached response, then reliability improves, but device complexity and processing time increase
Solution Approach 1:
The system segments the permission verification process into distinct components: metadata extraction, permission policy evaluation, and cache validation. By dividing the complex verification task into separate modules, the system improves reliability through thorough checking while reducing overall complexity through modular design and specialization.
Solution Approach 2:
The system applies partial verification by checking only the necessary permission attributes for each cached entry rather than performing exhaustive verification. It verifies user access rights and document citations when needed, but skips redundant checks for obviously authorized users or publicly accessible documents, balancing thoroughness with efficiency.
3Reliability
If the system purges cached data based on dynamic permission changes, then reliability improves, but loss of information and processing overhead increase
Solution Approach 1:
The system extracts only the necessary information (user IDs, document citations, timestamps) from cached responses and stores this metadata separately from the actual response content. When permission changes require purging, the system can quickly identify and remove only the affected entries using the extracted metadata, minimizing information loss and reducing processing overhead compared to scanning entire cache contents.
Data Source
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AI summary
A Content Distribution Network (CDN) may implemented as a front door to a RAG-based LLM for the purpose of semantically caching LLM responses to natural language prompts. More specifically, the CDN may also cache document citation(s) and/or user tag(s) along with the LLM response for purposes of ensuring that access permission constraints of the RAG are observed when providing cached LLM response as direct responses to semantically similar natural language prompts. Additionally, the CDN may be configured to modify and/or purge cached data from the CDN's cached memory database based on instructions received from a data access control (DAC) entity of the organization or enterprise client. This may ensure that the CDN observes any changes to the access permission constraints that might be made by the DAC entity.