Create metrics socket dir

Before this change, if the metrics socket was a unix socket, SOCI would
not create the parent dir before trying to bind. This exposed an
implicit dependency on bind order if you tried to put the metrics
address next to the main socket which we broke when we introduced
systemd socket activation.

This change ensures that we create the parent dir before binding the
metrics socket.

Signed-off-by: Kern Walster <walster@amazon.com>

cmd/soci-snapshotter-grpc/main.go

@@ -221,7 +221,13 @@ func serve(ctx context.Context, rpc *grpc.Server, addr string, rs snapshots.Snap
 
 	// We need to consider both the existence of MetricsAddress as well as NoPrometheus flag not set
 	if cfg.MetricsAddress != "" && !cfg.NoPrometheus {
-		l, err := net.Listen(cfg.MetricsNetwork, cfg.MetricsAddress)
+		var l net.Listener
+		var err error
+		if cfg.MetricsNetwork == "unix" {
+			l, err = listenUnix(cfg.MetricsAddress)
+		} else {
+			l, err = net.Listen(cfg.MetricsNetwork, cfg.MetricsAddress)
+		}
 		if err != nil {
 			return false, fmt.Errorf("failed to get listener for metrics endpoint: %w", err)
 		}

integration/startup_test.go

@@ -24,13 +24,23 @@ import (
 	shell "github.com/awslabs/soci-snapshotter/util/dockershell"
 )
 
+// Use a custom metrics config to test that the snapshotter
+// correctly starts up when the metrics address is next to the socket address.
+// This tests a regression with the first implementation of systemd socket activation
+// where we moved creation of the directory later which caused the metrics address
+// bind to fail. This verifies that the directory gets created before binding the metrics socket.
+const metricsConfig = `
+metrics_address="/run/soci-snapshotter-grpc/metrics.sock"
+metrics_network="unix"
+`
+
 // TestSnapshotterStartup tests to run containerd + snapshotter and check plugin is
 // recognized by containerd
 func TestSnapshotterStartup(t *testing.T) {
 	t.Parallel()
 	sh, done := newSnapshotterBaseShell(t)
 	defer done()
-	rebootContainerd(t, sh, "", "")
+	rebootContainerd(t, sh, "", getSnapshotterConfigToml(t, false, metricsConfig))
 	found := false
 	err := sh.ForEach(shell.C("ctr", "plugin", "ls"), func(l string) bool {
 		info := strings.Fields(l)