Update to the latest Prometheus.erl & Elli

[deadtrickster]

DO NOT MERGE

Metrics for 'normal' requests

• http_requests_total, counter. Total count of requests;
• http_request_duration_microseconds, histogram. The difference between request_end and request_start;
• http_request_headers_microseconds, histogram. The difference between headers_end and headers_start;
• http_request_body_microseconds, histogram. The difference between body_end and body_start;
• http_request_user_microseconds, histogram. The difference between user_end and user_start;
• http_request_send_microseconds, histogram. The difference between send_end and send_start;
• http_response_size_bytes, summary. Total size of the response, includes headers, body|file|chuncks;
• http_response_headers_size_bytes, summary. Size of the response headers;
• http_response_body_size, summary. Size of the response body.

Metrics for failed requests (network timeouts, malformed headers, etc)

• http_requests_failed_total{reason}, Total count of failed requests. Reasons:
  • request_closed - the client closes the connection when Elli is waiting for the next request;
  • request_timeout - the client times out when Elli is waiting for the request;
  • request_parse_error - the request is invalid and cannot be parsed or it contains a path Elli cannot parse or doesn't support;
  • client_closed - the client closes the connection or socket closed unexpectedly;
  • client_timeout - data can't be received within a timeout;
  • bad_request - Elli detects a request isn't well formatted or doesn't conform to the configured limits.
• http_bad_requests_total{reason} - Total count of bad_request errors. Reasons:
  • too_many_headers;
  • body_size.
• http_client_closed_total{request_part} - Total count of client_closed errors. Parts:
  • receiving_headers;
  • receiving_body;
  • before_response.
• http_client_timeout_total{request_part} Total count of client_timeout errors. Parts:
  • receiving_headers;
  • receiving_body.

[yurrriq]

Would a solution to https://github.com/elli-lib/elli/issues/3 help here? I'll leave this to you to merge.

[deadtrickster]

So I think this is usable enough and we can merge and move on. Let me know if you want to discuss metrics

[yurrriq]

Merging sounds good to me. Maybe you could add a simple example somewhere.

[deadtrickster]

Finally merged!