# Per-request metrics collection — records data after the response is sent.
  # Included in every prometheus-enabled app vhost. Metrics are labelled by
  # host + app so a single /metricz scrape on the prometheus domain covers all
  # applications without redundancy.
  log_by_lua_block {
    -- The metrics are defined together in prometheus.conf's init_worker. During an
    -- openresty reconverge a vhost can load before that init runs, so guard against
    -- a nil metric (otherwise log_by_lua throws "index global 'metric_requests'").
    if metric_requests then
      metric_requests:inc(1, {ngx.var.host, ngx.var.app_id, ngx.var.request_method, ngx.var.status})
      metric_latency:observe(tonumber(ngx.var.request_time), {ngx.var.host, ngx.var.app_id})
      metric_bytes_sent:inc(tonumber(ngx.var.bytes_sent) or 0, {ngx.var.host, ngx.var.app_id})
      metric_bytes_received:inc(tonumber(ngx.var.request_length) or 0, {ngx.var.host, ngx.var.app_id})
      if ngx.var.ssl_protocol and ngx.var.ssl_protocol ~= "" then
        metric_tls_handshakes:inc(1, {ngx.var.host, ngx.var.app_id, ngx.var.ssl_protocol})
      end
    end
  }