metrics HTTP server replacing the periodic "stats" logging

and example prometheus.yml file to use it as a scraping target

examples/prometheus.yml

@@ -0,0 +1,8 @@
+global:
+  scrape_interval: 1s
+
+scrape_configs:
+  - job_name: "nimbus"
+    static_configs:
+      - targets: ['localhost:9093']
+

nimbus/config.nim

@@ -135,6 +135,7 @@ type
     staticNodes*: seq[ENode]      ## List of static nodes to connect to
     bindPort*: uint16             ## Main TCP bind port
     discPort*: uint16             ## Discovery UDP bind port
+    metricsPort*: uint16          ## metrics HTTP server port
     maxPeers*: int                ## Maximum allowed number of peers
     maxPendingPeers*: int         ## Maximum allowed pending peers
     networkId*: uint              ## Network ID as integer
@@ -493,6 +494,11 @@ proc processNetArguments(key, value: string): ConfigStatus =
     result = processInteger(value, res)
     if result == Success:
       config.net.discPort = uint16(res and 0xFFFF)
+  elif skey == "metricsport":
+    var res = 0
+    result = processInteger(value, res)
+    if result == Success:
+      config.net.metricsPort = uint16(res and 0xFFFF)
   elif skey == "maxpeers":
     var res = 0
     result = processInteger(value, res)
@@ -626,6 +632,7 @@ proc initConfiguration(): NimbusConfiguration =
   result.net.maxPendingPeers = 0
   result.net.bindPort = 30303'u16
   result.net.discPort = 30303'u16
+  result.net.metricsPort = 9093'u16
   result.net.ident = NimbusIdent
   result.net.nat = NatAny
   result.net.protocols = defaultProtocols
@@ -675,6 +682,7 @@ NETWORKING OPTIONS:
   --staticnodes:<value>   Comma separated enode URLs to connect with
   --port:<value>          Network listening TCP port (default: 30303)
   --discport:<value>      Network listening UDP port (defaults to --port argument)
+  --metricsport:<value>   Metrics HTTP server port on localhost (defaults to 9093, set to 0 to disable)
   --maxpeers:<value>      Maximum number of network peers (default: 25)
   --maxpendpeers:<value>  Maximum number of pending connection attempts (default: 0)
   --nat:<value>           NAT port mapping mechanism (any|none|upnp|pmp|<external IP>) (default: "any")

nimbus/nimbus.nim

@@ -15,7 +15,7 @@ import
   eth/p2p/rlpx_protocols/[eth_protocol, les_protocol, whisper_protocol],
   eth/p2p/blockchain_sync, eth/net/nat, eth/p2p/peer_pool,
   config, genesis, rpc/[common, p2p, debug, whisper], p2p/chain,
-  eth/trie/db
+  eth/trie/db, metrics
 
 ## TODO:
 ## * No IPv6 support
@@ -136,14 +136,11 @@ proc start() =
       result = "EXITING"
     nimbus.rpcServer.start()
 
-  # periodically log internal statistics
+  # metrics
-  let statsInterval = 10.seconds
+  if conf.net.metricsPort > 0.uint16:
-  proc printStats(udata: pointer) {.closure, gcsafe.} =
+    let metricsAddress = "127.0.0.1"
-    {.gcsafe.}:
+    info "Starting metrics HTTP server", address = metricsAddress, port = conf.net.metricsPort
-      let peers = peerGauge.value.int64
+    metrics.startHttpServer(metricsAddress, Port(conf.net.metricsPort))
-    info "stats", peers
-    addTimer(Moment.fromNow(statsInterval), printStats)
-  addTimer(Moment.fromNow(statsInterval), printStats)
 
   # Connect directly to the static nodes
   for enode in conf.net.staticNodes: