feat: new metric for enabled jails (#1)

Add a new prometheus metric to track which jails are currently enabled.
Add a new database query to read the jail name and enabled status from the
database.
Add new metric to readme file.

README.md

@@ -99,6 +99,7 @@ Access exported metrics at `/metrics` (on the provided port).
 
 Exposed metrics:
 * `up` - Returns 1 if the service is up
+* `enabled_jails` - Returns 1 for each jail that is enabled, 0 if disabled.
 * `bad_ips` (per jail)
     * A *bad IP* is defined as an IP that has been banned at least once in the past
     * Bad IPs are counted per jail
@@ -120,4 +121,8 @@ fail2ban_banned_ips{jail="jail2"} 2
 # HELP fail2ban_up Was the last fail2ban query successful.
 # TYPE fail2ban_up gauge
 fail2ban_up 1
+# HELP fail2ban_enabled_jails Enabled jails.
+# TYPE fail2ban_enabled_jails gauge
+fail2ban_enabled_jails{jail="jail1"} 1
+fail2ban_enabled_jails{jail="jail2"} 1
 ```

src/db/db.go

@@ -8,6 +8,7 @@ import (
 
 const queryBadIpsPerJail = "SELECT j.name, (SELECT COUNT(1) FROM bips b WHERE j.name = b.jail) FROM jails j"
 const queryBannedIpsPerJail = "SELECT j.name, (SELECT COUNT(1) FROM bans b WHERE j.name = b.jail) FROM jails j"
+const queryJailNameToEnabled = "SELECT j.name, j.enabled FROM jails j"
 
 type Fail2BanDB struct {
 	DatabasePath string
@@ -36,6 +37,10 @@ func (db *Fail2BanDB) CountBadIpsPerJail() (map[string]int, error) {
 	return db.RunJailNameToCountQuery(queryBadIpsPerJail)
 }
 
+func (db *Fail2BanDB) JailNameToEnabledValue() (map[string]int, error) {
+	return db.RunJailNameToCountQuery(queryJailNameToEnabled)
+}
+
 func (db *Fail2BanDB) RunJailNameToCountQuery(query string) (map[string]int, error) {
 	stmt, err := db.sqliteDB.Prepare(query)
 	defer db.mustCloseStatement(stmt)

src/exporter.go

@@ -34,6 +34,11 @@ var (
 		"Number of bad IPs stored in the database (per jail).",
 		[]string{"jail"}, nil,
 	)
+	metricEnabledJails = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, "", "enabled_jails"),
+		"Enabled jails.",
+		[]string{"jail"}, nil,
+	)
 )
 
 type Exporter struct {
@@ -44,6 +49,7 @@ func (e *Exporter) Describe(ch chan<- *prometheus.Desc) {
 	ch <- metricUp
 	ch <- metricBadIpsPerJail
 	ch <- metricBannedIpsPerJail
+	ch <- metricEnabledJails
 }
 
 func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
@@ -52,6 +58,7 @@ func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
 	)
 	e.collectBadIpsPerJailMetrics(ch)
 	e.collectBannedIpsPerJailMetrics(ch)
+	e.collectEnabledJailMetrics(ch)
 }
 
 func (e *Exporter) collectBadIpsPerJailMetrics(ch chan<- prometheus.Metric) {
@@ -80,6 +87,19 @@ func (e *Exporter) collectBannedIpsPerJailMetrics(ch chan<- prometheus.Metric) {
 	}
 }
 
+func (e *Exporter) collectEnabledJailMetrics(ch chan<- prometheus.Metric) {
+	jailNameToEnabledMap, err := e.db.JailNameToEnabledValue()
+	if err != nil {
+		log.Print(err)
+	}
+
+	for jailName, count := range jailNameToEnabledMap {
+		ch <- prometheus.MustNewConstMetric(
+			metricEnabledJails, prometheus.GaugeValue, float64(count), jailName,
+		)
+	}
+}
+
 func printAppVersion() {
 	fmt.Println(version)
 	fmt.Printf("    build date:  %s\r\n    commit hash: %s\r\n    built by:    %s\r\n", date, commit, builtBy)