Elli middleware for collecting stats via Prometheus.

How Elli represents timings:

request_start
    headers_start
    ...headers receiving &  parsing...
    headers_end

    body_start
    ...body receiving & parsing...
    body_end

    user_start
    ...callback code...
    user_end

   send_start
   ...sending reply....
   send_end
request_end

How Elli represents sizes:

Each request has resp_headers key and, depending on response type, resp_body or file or chunks key.

• resp_header is always present and denotes response headers wire size;
• resp_body set for regular responses;
• file set for file responses;
• chunks set for chunked responses, wire size too.

Elli_prometheus exports the following metrics:

• 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;

For failed requests:

• 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.

Exporter metrics:

• telemetry_scrape_duration_seconds
  Type: summary.
  Labels: registry, content_type.
  Scrape duration.

• telemetry_scrape_size_bytes
  Type: summary.
  Labels: registry, content_type.
  Scrape size, not encoded.

• telemetry_scrape_encoded_size_bytes
  Type: summary.
  Labels: registry, content_type, encoding.
  Scrape size, encoded.

elli_prometheus requires Elli and Prometheus, but neither are included in this project. It has been tested and is known to work with {elli, "2.0.1"} and {prometheus, "3.1.1"}.