Add input plugin for Fail2ban (#2875)

plugins/inputs/fail2ban/fail2ban.go

@@ -0,0 +1,135 @@
+// +build linux
+
+package fail2ban
+
+import (
+	"errors"
+	"fmt"
+	"os/exec"
+	"strings"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/plugins/inputs"
+	"strconv"
+)
+
+var (
+	execCommand = exec.Command // execCommand is used to mock commands in tests.
+)
+
+type Fail2ban struct {
+	path    string
+	UseSudo bool
+}
+
+var sampleConfig = `
+  ## fail2ban-client require root access.
+  ## Setting 'use_sudo' to true will make use of sudo to run fail2ban-client.
+  ## Users must configure sudo to allow telegraf user to run fail2ban-client with no password.
+  ## This plugin run only "fail2ban-client status".
+  use_sudo = false
+`
+
+var metricsTargets = []struct {
+	target string
+	field  string
+}{
+	{
+		target: "Currently failed:",
+		field:  "failed",
+	},
+	{
+		target: "Currently banned:",
+		field:  "banned",
+	},
+}
+
+func (f *Fail2ban) Description() string {
+	return "Read metrics from fail2ban."
+}
+
+func (f *Fail2ban) SampleConfig() string {
+	return sampleConfig
+}
+
+func (f *Fail2ban) Gather(acc telegraf.Accumulator) error {
+	if len(f.path) == 0 {
+		return errors.New("fail2ban-client not found: verify that fail2ban is installed and that fail2ban-client is in your PATH")
+	}
+
+	name := f.path
+	var arg []string
+
+	if f.UseSudo {
+		name = "sudo"
+		arg = append(arg, f.path)
+	}
+
+	args := append(arg, "status")
+
+	cmd := execCommand(name, args...)
+	out, err := cmd.Output()
+	if err != nil {
+		return fmt.Errorf("failed to run command %s: %s - %s", strings.Join(cmd.Args, " "), err, string(out))
+	}
+	lines := strings.Split(string(out), "\n")
+	const targetString = "Jail list:"
+	var jails []string
+	for _, line := range lines {
+		idx := strings.LastIndex(line, targetString)
+		if idx < 0 {
+			// not target line, skip.
+			continue
+		}
+		jails = strings.Split(strings.TrimSpace(line[idx+len(targetString):]), ", ")
+		break
+	}
+
+	for _, jail := range jails {
+		fields := make(map[string]interface{})
+		args := append(arg, "status", jail)
+		cmd := execCommand(name, args...)
+		out, err := cmd.Output()
+		if err != nil {
+			return fmt.Errorf("failed to run command %s: %s - %s", strings.Join(cmd.Args, " "), err, string(out))
+		}
+
+		lines := strings.Split(string(out), "\n")
+		for _, line := range lines {
+			key, value := extractCount(line)
+			if key != "" {
+				fields[key] = value
+			}
+		}
+		acc.AddFields("fail2ban", fields, map[string]string{"jail": jail})
+	}
+	return nil
+}
+
+func extractCount(line string) (string, int) {
+	for _, metricsTarget := range metricsTargets {
+		idx := strings.LastIndex(line, metricsTarget.target)
+		if idx < 0 {
+			continue
+		}
+		ban := strings.TrimSpace(line[idx+len(metricsTarget.target):])
+		banCount, err := strconv.Atoi(ban)
+		if err != nil {
+			return "", -1
+		}
+		return metricsTarget.field, banCount
+	}
+	return "", -1
+}
+
+func init() {
+	f := Fail2ban{}
+	path, _ := exec.LookPath("fail2ban-client")
+	if len(path) > 0 {
+		f.path = path
+	}
+	inputs.Add("fail2ban", func() telegraf.Input {
+		f := f
+		return &f
+	})
+}