feat: support for textfile metrics (#13)

Add support for collecting arbitrary metrics from a textfile as well as
metrics collected from fail2ban. This allows other data to be exported
along with the fail2ban metrics (e.g. instance metadata).
Update the docker image to allow mounting a folder with a collection of
metric files to be exported. Only files ending in `.prom` with be read.
Update project README with the new functionality.

README.md

@@ -52,6 +52,10 @@ $ fail2ban-prometheus-exporter -h
         path to the fail2ban server socket
   -version
         show version info and exit
+  -collector.textfile
+        enable the textfile collector
+  -collector.textfile.directory string
+        directory to read text files with metrics from
 ```
 
 **Example**
@@ -240,3 +244,24 @@ fail2ban_errors{type="db"} 0
 # TYPE fail2ban_up gauge
 fail2ban_up 1
 ```
+
+### 4.3. Textfile Metrics
+
+For more flexibility the exporter also allows exporting metrics collected from a text file.
+
+To enable textfile metrics:
+1. Enable the collector with `-collector.textfile=true`
+2. Provide the directory to read files from with the `-collector.textfile.directory` flag
+
+Metrics collected from these files will be exposed directly alongside the other metrics without any additional processing.
+This means that it is the responsibility of the file creator to ensure the format is correct.
+
+By exporting textfile metrics an extra metric is also exported with an error count for each file:
+
+```
+# HELP textfile_error Checks for errors while reading text files
+# TYPE textfile_error gauge
+textfile_error{path="file.prom"} 0
+```
+
+**NOTE:** Any file not ending with `.prom` will be ignored.

docker/run.sh

@@ -5,6 +5,8 @@
 
 db_path=/app/fail2ban.sqlite3
 socket_path=/var/run/fail2ban/fail2ban.sock
+textfile_dir=/app/textfile/
+textfile_enabled=false
 
 # Blank out the file paths if they do not exist - a hacky way to only use these files if they were mounted into the container.
 if [ ! -f "$db_path" ]; then
@@ -13,9 +15,14 @@ fi
 if [ ! -S "$socket_path" ]; then
     socket_path=""
 fi
+if [ -d $textfile_dir ]; then
+    textfile_enabled=true
+fi
 
 # Start the exporter (use exec to support graceful shutdown)
 # Inspired by: https://akomljen.com/stopping-docker-containers-gracefully/
 exec /app/fail2ban-prometheus-exporter \
     -db "$db_path" \
-    -socket "$socket_path"
+    -socket "$socket_path" \
+    -collector.textfile=$textfile_enabled \
+    -collector.textfile.directory="$textfile_dir"

src/cfg/cfg.go

@@ -16,6 +16,8 @@ type AppSettings struct {
 	MetricsPort          int
 	Fail2BanDbPath       string
 	Fail2BanSocketPath   string
+	FileCollectorPath    string
+	FileCollectorEnabled bool
 }
 
 func Parse() *AppSettings {
@@ -24,6 +26,8 @@ func Parse() *AppSettings {
 	flag.IntVar(&appSettings.MetricsPort, "port", 9191, "port to use for the metrics server")
 	flag.StringVar(&appSettings.Fail2BanDbPath, "db", "", "path to the fail2ban sqlite database (deprecated)")
 	flag.StringVar(&appSettings.Fail2BanSocketPath, "socket", "", "path to the fail2ban server socket")
+	flag.BoolVar(&appSettings.FileCollectorEnabled, "collector.textfile", false, "enable the textfile collector")
+	flag.StringVar(&appSettings.FileCollectorPath, "collector.textfile.directory", "", "directory to read text files with metrics from")
 
 	flag.Parse()
 	appSettings.validateFlags()
@@ -42,6 +46,10 @@ func (settings *AppSettings) validateFlags() {
 				minServerPort, maxServerPort, settings.MetricsPort)
 			flagsValid = false
 		}
+		if settings.FileCollectorEnabled && settings.FileCollectorPath == "" {
+			fmt.Printf("file collector directory path must not be empty if collector enabled\n")
+			flagsValid = false
+		}
 	}
 	if !flagsValid {
 		flag.Usage()

src/exporter.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fail2ban-prometheus-exporter/cfg"
 	"fail2ban-prometheus-exporter/export"
+	"fail2ban-prometheus-exporter/textfile"
 	"fmt"
 	"log"
 	"net/http"
@@ -43,6 +44,11 @@ func rootHtmlHandler(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func metricHandler(w http.ResponseWriter, r *http.Request, collector *textfile.Collector) {
+	promhttp.Handler().ServeHTTP(w, r)
+	collector.WriteTextFileMetrics(w, r)
+}
+
 func main() {
 	appSettings := cfg.Parse()
 	if appSettings.VersionMode {
@@ -55,8 +61,13 @@ func main() {
 		exporter := export.NewExporter(appSettings, version)
 		prometheus.MustRegister(exporter)
 
+		textFileCollector := textfile.NewCollector(appSettings)
+		prometheus.MustRegister(textFileCollector)
+
 		http.HandleFunc("/", rootHtmlHandler)
-		http.Handle(metricsPath, promhttp.Handler())
+		http.HandleFunc(metricsPath, func(w http.ResponseWriter, r *http.Request) {
+			metricHandler(w, r, textFileCollector)
+		})
 		log.Printf("metrics available at '%s'", metricsPath)
 
 		svrErr := make(chan error)

src/textfile/collector.go

@@ -0,0 +1,48 @@
+package textfile
+
+import (
+	"fail2ban-prometheus-exporter/cfg"
+	"github.com/prometheus/client_golang/prometheus"
+	"log"
+)
+
+type Collector struct {
+	enabled    bool
+	folderPath string
+	fileMap    map[string]*fileData
+}
+
+type fileData struct {
+	readErrors   int
+	fileName     string
+	fileContents []byte
+}
+
+func NewCollector(appSettings *cfg.AppSettings) *Collector {
+	collector := &Collector{
+		enabled:    appSettings.FileCollectorEnabled,
+		folderPath: appSettings.FileCollectorPath,
+		fileMap:    make(map[string]*fileData),
+	}
+	if collector.enabled {
+		log.Printf("collector.textfile directory: %s", collector.folderPath)
+	}
+	return collector
+}
+
+func (c *Collector) Describe(ch chan<- *prometheus.Desc) {
+	if c.enabled {
+		ch <- metricReadError
+	}
+}
+
+func (c *Collector) Collect(ch chan<- prometheus.Metric) {
+	if c.enabled {
+		c.collectFileContents()
+		c.collectFileErrors(ch)
+	}
+}
+
+func (c *Collector) appendErrorForPath(path string) {
+	c.fileMap[path].readErrors++
+}

src/textfile/file.go

@@ -0,0 +1,55 @@
+package textfile
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"io/ioutil"
+	"log"
+	"path/filepath"
+	"strings"
+)
+
+const namespace = "textfile"
+
+var (
+	metricReadError = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, "", "error"),
+		"Checks for errors while reading text files",
+		[]string{"path"}, nil,
+	)
+)
+
+func (c *Collector) collectFileContents() {
+	files, err := ioutil.ReadDir(c.folderPath)
+	if err != nil {
+		log.Printf("error reading directory '%s': %v", c.folderPath, err)
+		return
+	}
+
+	for _, file := range files {
+		fileName := file.Name()
+		if !strings.HasSuffix(strings.ToLower(fileName), ".prom") {
+			continue
+		}
+		c.fileMap[fileName] = &fileData{
+			readErrors: 0,
+			fileName:   fileName,
+		}
+
+		fullPath := filepath.Join(c.folderPath, fileName)
+		content, err := ioutil.ReadFile(fullPath)
+		if err != nil {
+			c.appendErrorForPath(fileName)
+			log.Printf("error reading contents of file '%s': %v", fileName, err)
+		}
+
+		c.fileMap[fileName].fileContents = content
+	}
+}
+
+func (c *Collector) collectFileErrors(ch chan<- prometheus.Metric) {
+	for _, f := range c.fileMap {
+		ch <- prometheus.MustNewConstMetric(
+			metricReadError, prometheus.GaugeValue, float64(f.readErrors), f.fileName,
+		)
+	}
+}

src/textfile/writer.go

@@ -0,0 +1,20 @@
+package textfile
+
+import (
+	"log"
+	"net/http"
+)
+
+func (c *Collector) WriteTextFileMetrics(w http.ResponseWriter, r *http.Request) {
+	if !c.enabled {
+		return
+	}
+
+	for _, f := range c.fileMap {
+		_, err := w.Write(f.fileContents)
+		if err != nil {
+			c.appendErrorForPath(f.fileName)
+			log.Printf("error writing file contents to response writer '%s': %v", f.fileName, err)
+		}
+	}
+}