fix(inputs.chrony): use DGRAM for the unix socket

We must use the DGRAM type when connecting to the chrony socket. On top
of that, the socket must be duplicated in order to allow concurrent
calls to it.

Fixes #15549

Signed-off-by: Frank Villaro-Dixon <frank@villaro-dixon.eu>

plugins/inputs/chrony/README.md

@@ -42,6 +42,15 @@ See the [CONFIGURATION.md][CONFIGURATION.md] for more details.
   # metrics = ["tracking"]
 ```
 
+## Rights
+
+To use the unix socket, telegraf must be able to talk to it. Please ensure that
+the telegraf user is a member of the `chrony` group or telegraf won't be able to
+use the socket!
+
+The unix socket is needed in order to use the `serverstats` metrics. All other
+metrics can be gathered using the udp connection.
+
 ## Metrics
 
 - chrony

plugins/inputs/chrony/chrony.go

@@ -8,6 +8,8 @@ import (
 	"fmt"
 	"net"
 	"net/url"
+	"os"
+	"path"
 	"strconv"
 	"syscall"
 	"time"
@@ -38,6 +40,26 @@ func (*Chrony) SampleConfig() string {
 	return sampleConfig
 }
 
+// dialUnix opens an unixgram connection with chrony
+func dialUnix(address string) (*net.UnixConn, error) {
+	dir := path.Dir(address)
+	local := path.Join(dir, fmt.Sprintf("chronyc.%d.sock", os.Getpid()))
+	conn, err := net.DialUnix("unixgram",
+		&net.UnixAddr{Name: local, Net: "unixgram"},
+		&net.UnixAddr{Name: address, Net: "unixgram"},
+	)
+
+	if err != nil {
+		return nil, err
+	}
+
+	if err := os.Chmod(local, 0666); err != nil {
+		return nil, err
+	}
+
+	return conn, nil
+}
+
 func (c *Chrony) Init() error {
 	// Use the configured server, if none set, we try to guess it in Start()
 	if c.Server != "" {
@@ -47,7 +69,7 @@ func (c *Chrony) Init() error {
 			return fmt.Errorf("parsing server address failed: %w", err)
 		}
 		switch u.Scheme {
-		case "unix":
+		case "unixgram":
 			// Keep the server unmodified
 		case "udp":
 			// Check if we do have a port and add the default port if we don't
@@ -89,8 +111,8 @@ func (c *Chrony) Start(_ telegraf.Accumulator) error {
 			return fmt.Errorf("parsing server address failed: %w", err)
 		}
 		switch u.Scheme {
-		case "unix":
-			conn, err := net.DialTimeout("unix", u.Path, time.Duration(c.Timeout))
+		case "unixgram":
+			conn, err := dialUnix(u.Path)
 			if err != nil {
 				return fmt.Errorf("dialing %q failed: %w", c.Server, err)
 			}
@@ -106,7 +128,7 @@ func (c *Chrony) Start(_ telegraf.Accumulator) error {
 		}
 	} else {
 		// If no server is given, reproduce chronyc's behavior
-		if conn, err := net.DialTimeout("unix", "/run/chrony/chronyd.sock", time.Duration(c.Timeout)); err == nil {
+		if conn, err := dialUnix("/run/chrony/chronyd.sock"); err == nil {
 			c.Server = "unix:///run/chrony/chronyd.sock"
 			c.conn = conn
 		} else if conn, err := net.DialTimeout("udp", "127.0.0.1:323", time.Duration(c.Timeout)); err == nil {