add metric for max_conns of upstream servers (#201)

Author: Steven Hessing

README.md

@@ -173,6 +173,7 @@ Name | Type | Description | Labels
 ----|----|----|----|
 `nginxplus_upstream_server_state` | Gauge | Current state | `server`, `upstream` |
 `nginxplus_upstream_server_active` | Gauge | Active connections | `server`, `upstream` |
+`nginxplus_upstream_server_limit` | Gauge | Limit for connections which corresponds to the max_conns parameter of the upstream server. Zero value means there is no limit | `server`, `upstream` |
 `nginxplus_upstream_server_requests` | Counter | Total client requests | `server`, `upstream` |
 `nginxplus_upstream_server_responses` | Counter | Total responses sent to clients | `code` (the response status code. The values are: `1xx`, `2xx`, `3xx`, `4xx` and `5xx`), `server`, `upstream` |
 `nginxplus_upstream_server_sent` | Counter | Bytes sent to this server | `server`, `upstream` |
@@ -195,8 +196,9 @@ Name | Type | Description | Labels
 ----|----|----|----|
 `nginxplus_stream_upstream_server_state` | Gauge | Current state | `server`, `upstream` |
 `nginxplus_stream_upstream_server_active` | Gauge | Active connections | `server` , `upstream` |
+`nginxplus_stream_upstream_server_limit` | Gauge | Limit for connections which corresponds to the max_conns parameter of the upstream server. Zero value means there is no limit | `server` , `upstream` |
 `nginxplus_stream_upstream_server_connections` | Counter | Total number of client connections forwarded to this server | `server`, `upstream` |
-`nginxplus_stream_upstream_server_connect_time` | Gauge | Average time to connect to the upstream server | `server`, `upstream` 
+`nginxplus_stream_upstream_server_connect_time` | Gauge | Average time to connect to the upstream server | `server`, `upstream`
 `nginxplus_stream_upstream_server_first_byte_time` | Gauge | Average time to receive the first byte of data | `server`, `upstream` |
 `nginxplus_stream_upstream_server_response_time` | Gauge | Average time to receive the last byte of data | `server`, `upstream` |
 `nginxplus_stream_upstream_server_sent` | Counter | Bytes sent to this server | `server`, `upstream` |

collector/nginx_plus.go

@@ -273,6 +273,7 @@ func NewNginxPlusCollector(nginxClient *plusclient.NginxClient, namespace string
 		upstreamServerMetrics: map[string]*prometheus.Desc{
 			"state":                   newUpstreamServerMetric(namespace, "state", "Current state", upstreamServerVariableLabelNames, constLabels),
 			"active":                  newUpstreamServerMetric(namespace, "active", "Active connections", upstreamServerVariableLabelNames, constLabels),
+			"limit":                   newUpstreamServerMetric(namespace, "limit", "Limit for connections which corresponds to the max_conns parameter of the upstream server. Zero value means there is no limit", upstreamServerVariableLabelNames, constLabels),
 			"requests":                newUpstreamServerMetric(namespace, "requests", "Total client requests", upstreamServerVariableLabelNames, constLabels),
 			"responses_1xx":           newUpstreamServerMetric(namespace, "responses", "Total responses sent to clients", upstreamServerVariableLabelNames, MergeLabels(constLabels, prometheus.Labels{"code": "1xx"})),
 			"responses_2xx":           newUpstreamServerMetric(namespace, "responses", "Total responses sent to clients", upstreamServerVariableLabelNames, MergeLabels(constLabels, prometheus.Labels{"code": "2xx"})),
@@ -292,6 +293,7 @@ func NewNginxPlusCollector(nginxClient *plusclient.NginxClient, namespace string
 		streamUpstreamServerMetrics: map[string]*prometheus.Desc{
 			"state":                   newStreamUpstreamServerMetric(namespace, "state", "Current state", streamUpstreamServerVariableLabelNames, constLabels),
 			"active":                  newStreamUpstreamServerMetric(namespace, "active", "Active connections", streamUpstreamServerVariableLabelNames, constLabels),
+			"limit":                   newStreamUpstreamServerMetric(namespace, "limit", "Limit for connections which corresponds to the max_conns parameter of the upstream server. Zero value means there is no limit", streamUpstreamServerVariableLabelNames, constLabels),
 			"sent":                    newStreamUpstreamServerMetric(namespace, "sent", "Bytes sent to this server", streamUpstreamServerVariableLabelNames, constLabels),
 			"received":                newStreamUpstreamServerMetric(namespace, "received", "Bytes received from this server", streamUpstreamServerVariableLabelNames, constLabels),
 			"fails":                   newStreamUpstreamServerMetric(namespace, "fails", "Number of unsuccessful attempts to communicate with the server", streamUpstreamServerVariableLabelNames, constLabels),
@@ -511,6 +513,8 @@ func (c *NginxPlusCollector) Collect(ch chan<- prometheus.Metric) {
 				prometheus.GaugeValue, upstreamServerStates[peer.State], labelValues...)
 			ch <- prometheus.MustNewConstMetric(c.upstreamServerMetrics["active"],
 				prometheus.GaugeValue, float64(peer.Active), labelValues...)
+			ch <- prometheus.MustNewConstMetric(c.upstreamServerMetrics["limit"],
+				prometheus.GaugeValue, float64(peer.MaxConns), labelValues...)
 			ch <- prometheus.MustNewConstMetric(c.upstreamServerMetrics["requests"],
 				prometheus.CounterValue, float64(peer.Requests), labelValues...)
 			ch <- prometheus.MustNewConstMetric(c.upstreamServerMetrics["responses_1xx"],
@@ -582,6 +586,8 @@ func (c *NginxPlusCollector) Collect(ch chan<- prometheus.Metric) {
 				prometheus.GaugeValue, upstreamServerStates[peer.State], labelValues...)
 			ch <- prometheus.MustNewConstMetric(c.streamUpstreamServerMetrics["active"],
 				prometheus.GaugeValue, float64(peer.Active), labelValues...)
+			ch <- prometheus.MustNewConstMetric(c.streamUpstreamServerMetrics["limit"],
+				prometheus.GaugeValue, float64(peer.MaxConns), labelValues...)
 			ch <- prometheus.MustNewConstMetric(c.streamUpstreamServerMetrics["connections"],
 				prometheus.CounterValue, float64(peer.Connections), labelValues...)
 			ch <- prometheus.MustNewConstMetric(c.streamUpstreamServerMetrics["connect_time"],