Add node name validation to the catalog sync process

subcommand/sync-catalog/command.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"os"
 	"os/signal"
+	"regexp"
 	"sync"
 	"time"
 
@@ -97,7 +98,8 @@ func (c *Command) init() {
 	c.flags.StringVar(&c.flagConsulK8STag, "consul-k8s-tag", "k8s",
 		"Tag value for K8S services registered in Consul")
 	c.flags.StringVar(&c.flagConsulNodeName, "consul-node-name", "k8s-sync",
-		"The Consul node name to register for k8s-sync. Defaults to k8s-sync.")
+		"The Consul node name to register for catalog sync. Defaults to k8s-sync. To be discoverable "+
+			"via DNS, the name should only contain alpha-numerics and dashes.")
 	c.flags.DurationVar(&c.flagConsulWritePeriod, "consul-write-interval", 30*time.Second,
 		"The interval to perform syncing operations creating Consul services, formatted "+
 			"as a time.Duration. All changes are merged and write calls are only made "+
@@ -162,6 +164,12 @@ func (c *Command) Run(args []string) int {
 		return 1
 	}
 
+	// Validate flags
+	if err := c.validateFlags(); err != nil {
+		c.UI.Error(err.Error())
+		return 1
+	}
+
 	// Create the k8s clientset
 	if c.clientset == nil {
 		config, err := subcommand.K8SConfig(c.k8s.KubeConfig())
@@ -380,6 +388,31 @@ func (c *Command) interrupt() {
 	c.sigCh <- os.Interrupt
 }
 
+func (c *Command) validateFlags() error {
+	// For the Consul node name to be discoverable via DNS, it must contain only
+	// dashes and alphanumeric characters. Length is also constrained.
+	// These restrictions match those defined in Consul's agent definition.
+	var InvalidDnsRe = regexp.MustCompile(`[^A-Za-z0-9\\-]+`)
+	const MaxDNSLabelLength = 63
+
+	if InvalidDnsRe.MatchString(c.flagConsulNodeName) {
+		return fmt.Errorf("Node name will not be discoverable "+
+			"via DNS due to invalid characters. Valid characters include "+
+			"all alpha-numerics and dashes. consul-node-name=%s",
+			c.flagConsulNodeName,
+		)
+	}
+	if len(c.flagConsulNodeName) > MaxDNSLabelLength {
+		return fmt.Errorf("Node name will not be discoverable "+
+			"via DNS due to it being too long. Valid lengths are between "+
+			"1 and 63 bytes. consul-node-name=%s",
+			c.flagConsulNodeName,
+		)
+	}
+
+	return nil
+}
+
 const synopsis = "Sync Kubernetes services and Consul services."
 const help = `
 Usage: consul-k8s sync-catalog [options]

subcommand/sync-catalog/command_test.go

@@ -16,6 +16,39 @@ import (
 	"k8s.io/client-go/kubernetes/fake"
 )
 
+// Test flag validation
+func TestRun_FlagValidation(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		Flags  []string
+		ExpErr string
+	}{
+		{
+			Flags: []string{"-consul-node-name=Speci@l_Chars"},
+			ExpErr: "Node name will not be discoverable via DNS due to invalid characters. Valid characters include " +
+				"all alpha-numerics and dashes. consul-node-name=Speci@l_Chars",
+		},
+		{
+			Flags: []string{"-consul-node-name=5r9OPGfSRXUdGzNjBdAwmhCBrzHDNYs4XjZVR4wp7lSLIzqwS0ta51nBLIN0TMPV-too-long"},
+			ExpErr: "Node name will not be discoverable via DNS due to it being too long. Valid lengths are between " +
+				"1 and 63 bytes. consul-node-name=5r9OPGfSRXUdGzNjBdAwmhCBrzHDNYs4XjZVR4wp7lSLIzqwS0ta51nBLIN0TMPV-too-long",
+		},
+	}
+
+	for _, c := range cases {
+		t.Run(c.ExpErr, func(t *testing.T) {
+			ui := cli.NewMockUi()
+			cmd := Command{
+				UI: ui,
+			}
+			responseCode := cmd.Run(c.Flags)
+			require.Equal(t, 1, responseCode, ui.ErrorWriter.String())
+			require.Contains(t, ui.ErrorWriter.String(), c.ExpErr)
+		})
+	}
+}
+
 // Test that the default consul service is synced to k8s
 func TestRun_Defaults_SyncsConsulServiceToK8s(t *testing.T) {
 	t.Parallel()