ghCache

Mon, 01 Jan 0001 00:00:00 +0000

What?

ghCache is an HTTP cache optimized for caching responses from the GitHub API (https://api.github.com). Specifically, it has the following non-standard caching behavior:

Every cache hit is revalidated with a conditional HTTP request to GitHub regardless of cache entry freshness (TTL). The ‘Cache-Control’ header is ignored and overwritten to achieve this.
Concurrent requests for the same resource are coalesced and share a single request/response from GitHub instead of each request resulting in a corresponding upstream request and response.

ghCache also provides prometheus instrumentation to expose cache activity, request duration, and API token usage/savings.

Additional throttling algorithm

Mon, 01 Jan 0001 00:00:00 +0000

Motivation

An additional throttling algorithm was introduced to ghproxy to prevent secondary rate limiting issues (code 403) in large Prow installations, consisting of several organizations. Its purpose is to schedule incoming requests to adjust to the GitHub general rate-limiting guidelines.

Implementation

An incoming request is analyzed whether it is targeting GitHub API v3 or API v4. Separate queues are formed not only per API but also per organization if Prow installation is using GitHub Apps. If a user account in a form of the bot is used, every request coming from that user account is categorized as coming from the same organization. This is due to the fact, that such a request identifies not using AppID and organization name, but sha256 token hash.

ghProxy on Prow

ghCache

What?

Additional throttling algorithm

Motivation

Implementation