Handling rate limited requests

A GitLab instance may be behind a reverse proxy that has rate-limiting on API requests to prevent abuse. GitLab Runner sends multiple requests to the API and could go over these rate limits. As a result, GitLab Runner handles rate limited scenarios with the following logic:

1. A response code of 429 - TooManyRequests is received.
2. The response headers are checked for a RateLimit-ResetTime header. The RateLimit-ResetTime header should have a value which is a valid HTTP Date (RFC1123), like Wed, 21 Oct 2015 07:28:00 GMT.
   • If the header is present and has a valid value the Runner waits until the specified time and issues another request.
   • If the header is present, but isn’t a valid date, a fallback of 1 minute is used.
   • If the header is not present, no additional actions are taken, the response error is returned.
3. The process above is repeated 5 times, then a gave up due to rate limit error is returned.