Add gauges for allocated memory for queued UDP and TCP packages (#1503)

* Two new states will be added to the tcpstat collector called rx_queued_bytes and tx_queued_bytes.

For UDP datagrams an additional collector 'udp_queues' can be used to expose the total lengths of the tx_queue and rx_queue.
@SuperQ and @discordianfish this changes gives us the option to check for overloaded UDP + TCP processing.
The names of the new TCP states and the UDP metric can be discussed.
The current reasons are just:

I don't want to add another collector for the same exposed file, so I just added the new states to the tcpstat collector.
I chose the name 'udp_queue' instead of 'udpstat' as UDP has no state.


Signed-off-by: Peter Bueschel <peter.bueschel@logmein.com>

collector/udp_queues_linux.go

@@ -0,0 +1,87 @@
+// Copyright 2015 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !noudp_queues
+
+package collector
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/go-kit/kit/log"
+	"github.com/go-kit/kit/log/level"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/procfs"
+)
+
+type (
+	udpQueuesCollector struct {
+		fs     procfs.FS
+		desc   *prometheus.Desc
+		logger log.Logger
+	}
+)
+
+func init() {
+	registerCollector("udp_queues", defaultEnabled, NewUDPqueuesCollector)
+}
+
+// NewUDPqueuesCollector returns a new Collector exposing network udp queued bytes.
+func NewUDPqueuesCollector(logger log.Logger) (Collector, error) {
+	fs, err := procfs.NewFS(*procPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open procfs: %v", err)
+	}
+	return &udpQueuesCollector{
+		fs: fs,
+		desc: prometheus.NewDesc(
+			prometheus.BuildFQName(namespace, "udp", "queues"),
+			"Number of allocated memory in the kernel for UDP datagrams in bytes.",
+			[]string{"queue", "ip"}, nil,
+		),
+		logger: logger,
+	}, nil
+}
+
+func (c *udpQueuesCollector) Update(ch chan<- prometheus.Metric) error {
+
+	s4, errIPv4 := c.fs.NetUDPSummary()
+	if errIPv4 == nil {
+		ch <- prometheus.MustNewConstMetric(c.desc, prometheus.GaugeValue, float64(s4.TxQueueLength), "tx", "v4")
+		ch <- prometheus.MustNewConstMetric(c.desc, prometheus.GaugeValue, float64(s4.RxQueueLength), "rx", "v4")
+	} else {
+		if os.IsNotExist(errIPv4) {
+			level.Debug(c.logger).Log("msg", "not collecting ipv4 based metrics")
+		} else {
+			return fmt.Errorf("couldn't get upd queued bytes: %s", errIPv4)
+		}
+	}
+
+	s6, errIPv6 := c.fs.NetUDP6Summary()
+	if errIPv6 == nil {
+		ch <- prometheus.MustNewConstMetric(c.desc, prometheus.GaugeValue, float64(s6.TxQueueLength), "tx", "v6")
+		ch <- prometheus.MustNewConstMetric(c.desc, prometheus.GaugeValue, float64(s6.RxQueueLength), "rx", "v6")
+	} else {
+		if os.IsNotExist(errIPv6) {
+			level.Debug(c.logger).Log("msg", "not collecting ipv6 based metrics")
+		} else {
+			return fmt.Errorf("couldn't get upd6 queued bytes: %s", errIPv6)
+		}
+	}
+
+	if os.IsNotExist(errIPv4) && os.IsNotExist(errIPv6) {
+		return ErrNoData
+	}
+	return nil
+}