Add metric to track number ssh connect attempts

docs/pages/setup/reference/metrics.mdx

@@ -112,6 +112,7 @@ Now you can see the monitoring information by visiting several endpoints:
 | `teleport_build_info` | gauge | Teleport | Provides build information of Teleport including gitref (git describe --long --tags), Go version, and Teleport version. The value of this gauge will always be 1. |
 | `teleport_cache_events` | counter | Teleport | Number of events received by a Teleport service cache. Teleport's Auth Service, Proxy Service, and other services cache incoming events related to their service. |
 | `teleport_cache_stale_events` | counter | Teleport | Number of stale events received by a Teleport service cache. A high percentage of stale events can indicate a degraded backend. |
+| `teleport_connect_to_node_attempts_total` | gauge | Teleport Proxy | Number of ssh connection attempts to a node. |
 | `teleport_connected_resources` | gauge | Teleport Auth | Tracks the number and type of resources connected via keepalives. |
 | `teleport_registered_servers` | gauge | Teleport Auth | The number of Teleport servers (a server consists of one or more Teleport services) that have connected to the Teleport cluster, including the Teleport version. After disconnecting, a Teleport server has a TTL of 10 minutes, so this value will include servers that have recently disconnected but have not reached their TTL. |
 | `teleport_reverse_tunnels_connected` | gauge | Teleport Proxy | Number of reverse SSH tunnels connected to the Teleport Proxy Service by Teleport instances. |

lib/srv/regular/proxy.go

@@ -59,7 +59,15 @@ var ( // failedConnectingToNode counts failed attempts to connect to a node
 		},
 	)
 
-	prometheusCollectors = []prometheus.Collector{proxiedSessions, failedConnectingToNode}
+	connectingToNode = prometheus.NewCounter(
+		prometheus.CounterOpts{
+			Namespace: teleport.MetricNamespace,
+			Name:      teleport.MetricConnectToNodeAttempts,
+			Help:      "Number of ssh connection attempts to a node.",
+		},
+	)
+
+	prometheusCollectors = []prometheus.Collector{proxiedSessions, failedConnectingToNode, connectingToNode}
 )
 
 // proxySubsys implements an SSH subsystem for proxying listening sockets from
@@ -405,6 +413,7 @@ func (t *proxySubsys) proxyToHost(
 		AddrNetwork: "tcp",
 		Addr:        serverAddr,
 	}
+	connectingToNode.Inc()
 	conn, err := site.Dial(reversetunnel.DialParams{
 		From:         remoteAddr,
 		To:           toAddr,

metrics.go

@@ -49,6 +49,9 @@ const (
 	// MetricFailedLoginAttempts counts failed login attempts
 	MetricFailedLoginAttempts = "failed_login_attempts_total"
 
+	// MetricConnectToNodeAttempts counts ssh attempts
+	MetricConnectToNodeAttempts = "connect_to_node_attempts_total"
+
 	// MetricFailedConnectToNodeAttempts counts failed ssh attempts
 	MetricFailedConnectToNodeAttempts = "failed_connect_to_node_attempts_total"