USHIFT-6902 USHIFT-6903: Custom DNS configuration

cmd/generate-config/config/config-openapi-spec.json

@@ -245,6 +245,11 @@
           "default": "example.com",
           "example": "microshift.example.com"
         },
+        "configFile": {
+          "description": "configFile is the path to a custom CoreDNS Corefile on the host filesystem.\nWhen set, MicroShift uses this file as the Corefile in the dns-default ConfigMap,\nfully replacing the default template-rendered configuration.\nChanges to this file are detected at runtime and applied without restarting MicroShift.\nMutually exclusive with dns.hosts: setting both causes a startup error.",
+          "type": "string",
+          "example": "/etc/microshift/dns/Corefile"
+        },
         "hosts": {
           "description": "Hosts contains configuration for the hosts file.",
           "type": "object",

docs/user/howto_config.md

@@ -40,6 +40,7 @@ debugging:
     logLevel: ""
 dns:
     baseDomain: ""
+    configFile: ""
     hosts:
         file: ""
         status: ""
@@ -198,6 +199,7 @@ debugging:
     logLevel: Normal
 dns:
     baseDomain: example.com
+    configFile: ""
     hosts:
         file: /etc/hosts
         status: Disabled

packaging/microshift/config.yaml

@@ -72,6 +72,14 @@ dns:
     # example:
     #   microshift.example.com
     baseDomain: example.com
+    # configFile is the path to a custom CoreDNS Corefile on the host filesystem.
+    # When set, MicroShift uses this file as the Corefile in the dns-default ConfigMap,
+    # fully replacing the default template-rendered configuration.
+    # Changes to this file are detected at runtime and applied without restarting MicroShift.
+    # Mutually exclusive with dns.hosts: setting both causes a startup error.
+    # example:
+    #   /etc/microshift/dns/Corefile
+    configFile: ""
     # Hosts contains configuration for the hosts file.
     hosts:
         # File is the path to the hosts file to monitor.

pkg/cmd/run.go

@@ -236,6 +236,7 @@ func RunMicroshift(cfg *config.Config) error {
 	util.Must(m.AddService(controllers.NewClusterID(cfg)))
 	util.Must(m.AddService(controllers.NewTelemetryManager(cfg)))
 	util.Must(m.AddService(controllers.NewHostsWatcherManager(cfg)))
+	util.Must(m.AddService(controllers.NewDNSConfigurationWatcherManager(cfg)))
 	util.Must(m.AddService(gdp.NewGenericDevicePlugin(cfg)))
 
 	// Storing and clearing the env, so other components don't send the READY=1 until MicroShift is fully ready

pkg/components/controllers.go

@@ -291,10 +291,9 @@ func startDNSController(ctx context.Context, cfg *config.Config, kubeconfigPath
 			"components/openshift-dns/dns/service-account.yaml",
 			"components/openshift-dns/node-resolver/service-account.yaml",
 		}
-		cm = []string{
-			"components/openshift-dns/dns/configmap.yaml",
-		}
-		svc = []string{
+		cm     = "components/openshift-dns/dns/configmap.yaml"
+		cmList = []string{cm}
+		svc    = []string{
 			"components/openshift-dns/dns/service.yaml",
 		}
 	)
@@ -303,9 +302,10 @@ func startDNSController(ctx context.Context, cfg *config.Config, kubeconfigPath
 		return err
 	}
 
+	hostsEnabled := cfg.DNS.Hosts.Status == config.HostsStatusEnabled
 	extraParams := assets.RenderParams{
 		"ClusterIP":    cfg.Network.DNS,
-		"HostsEnabled": cfg.DNS.Hosts.Status == config.HostsStatusEnabled,
+		"HostsEnabled": hostsEnabled,
 	}
 
 	if err := assets.ApplyServices(ctx, svc, renderTemplate, renderParamsFromConfig(cfg, extraParams), kubeconfigPath); err != nil {
@@ -333,10 +333,24 @@ func startDNSController(ctx context.Context, cfg *config.Config, kubeconfigPath
 		klog.Warningf("Failed to apply serviceAccount %v %v", sa, err)
 		return err
 	}
-	if err := assets.ApplyConfigMaps(ctx, cm, renderTemplate, renderParamsFromConfig(cfg, extraParams), kubeconfigPath); err != nil {
-		klog.Warningf("Failed to apply configMap %v %v", cm, err)
-		return err
+
+	if cfg.DNS.ConfigFile != "" {
+		corefileContent, err := os.ReadFile(cfg.DNS.ConfigFile)
+		if err != nil {
+			klog.Warningf("Failed to read custom DNS config file %s: %v", cfg.DNS.ConfigFile, err)
+			return err
+		}
+		if err := assets.ApplyConfigMapWithData(ctx, cm, map[string]string{"Corefile": string(corefileContent)}, kubeconfigPath); err != nil {
+			klog.Warningf("Failed to apply custom DNS configMap: %v", err)
+			return err
+		}
+	} else {
+		if err := assets.ApplyConfigMaps(ctx, cmList, renderTemplate, renderParamsFromConfig(cfg, extraParams), kubeconfigPath); err != nil {
+			klog.Warningf("Failed to apply configMap %v %v", cmList, err)
+			return err
+		}
 	}
+
 	if err := assets.ApplyDaemonSets(ctx, apps, renderTemplate, renderParamsFromConfig(cfg, extraParams), kubeconfigPath); err != nil {
 		klog.Warningf("Failed to apply apps %v %v", apps, err)
 		return err

pkg/config/config.go

@@ -212,6 +212,9 @@ func (c *Config) incorporateUserSettings(u *Config) {
 	if u.DNS.BaseDomain != "" {
 		c.DNS.BaseDomain = u.DNS.BaseDomain
 	}
+	if u.DNS.ConfigFile != "" {
+		c.DNS.ConfigFile = u.DNS.ConfigFile
+	}
 
 	if u.Network.CNIPlugin != "" {
 		c.Network.CNIPlugin = u.Network.CNIPlugin

pkg/config/dns.go

@@ -27,6 +27,15 @@ type DNS struct {
 	// +kubebuilder:example=microshift.example.com
 	BaseDomain string `json:"baseDomain"`
 
+	// configFile is the path to a custom CoreDNS Corefile on the host filesystem.
+	// When set, MicroShift uses this file as the Corefile in the dns-default ConfigMap,
+	// fully replacing the default template-rendered configuration.
+	// Changes to this file are detected at runtime and applied without restarting MicroShift.
+	// Mutually exclusive with dns.hosts: setting both causes a startup error.
+	// +optional
+	// +kubebuilder:example="/etc/microshift/dns/Corefile"
+	ConfigFile string `json:"configFile,omitempty"`
+
 	// Hosts contains configuration for the hosts file.
 	Hosts HostsConfig `json:"hosts,omitempty"`
 }
@@ -59,6 +68,53 @@ func dnsDefaults() DNS {
 }
 
 func (t *DNS) validate() error {
+	if t.ConfigFile != "" && t.Hosts.Status == HostsStatusEnabled {
+		return fmt.Errorf("dns.configFile and dns.hosts are mutually exclusive")
+	}
+
+	if err := t.validateConfigFile(); err != nil {
+		return err
+	}
+
+	return t.validateHosts()
+}
+
+func (t *DNS) validateConfigFile() error {
+	if t.ConfigFile == "" {
+		return nil
+	}
+
+	cleanPath := filepath.Clean(t.ConfigFile)
+	if !filepath.IsAbs(cleanPath) {
+		return fmt.Errorf("dns config file path must be absolute: got %s", t.ConfigFile)
+	}
+
+	fi, err := os.Stat(cleanPath)
+	if os.IsNotExist(err) {
+		return fmt.Errorf("dns config file %s does not exist", t.ConfigFile)
+	} else if err != nil {
+		return fmt.Errorf("error checking dns config file %s: %v", t.ConfigFile, err)
+	}
+	if !fi.Mode().IsRegular() {
+		return fmt.Errorf("dns config file %s must be a regular file", t.ConfigFile)
+	}
+
+	if fi.Size() == 0 {
+		return fmt.Errorf("dns config file %s is empty", t.ConfigFile)
+	}
+
+	if fi.Size() > 1048576 {
+		return fmt.Errorf("dns config file %s exceeds 1MiB ConfigMap size limit (got %d bytes)", t.ConfigFile, fi.Size())
+	}
+
+	file, err := os.Open(cleanPath)
+	if err != nil {
+		return fmt.Errorf("dns config file %s is not readable: %v", t.ConfigFile, err)
+	}
+	return file.Close()
+}
+
+func (t *DNS) validateHosts() error {
 	switch t.Hosts.Status {
 	case HostsStatusEnabled:
 		if t.Hosts.File == "" {
@@ -68,7 +124,6 @@ func (t *DNS) validate() error {
 		cleanPath := filepath.Clean(t.Hosts.File)
 
 		fi, err := os.Stat(cleanPath)
-		// Enforce ConfigMap requirement: the file must not exceed 1MiB, as it will be mounted into a ConfigMap.
 		if err == nil && fi.Size() > 1048576 {
 			return fmt.Errorf("hosts file %s exceeds 1MiB ConfigMap (and internal buffer) size limit (got %d bytes)", t.Hosts.File, fi.Size())
 		}

pkg/config/dns_test.go

@@ -0,0 +1,141 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDNS_ValidateConfigFile_MutualExclusivity(t *testing.T) {
+	tmpFile := createTempCorefile(t, ".:5353 { whoami }")
+
+	dns := DNS{
+		ConfigFile: tmpFile,
+		Hosts: HostsConfig{
+			Status: HostsStatusEnabled,
+			File:   "/etc/hosts",
+		},
+	}
+	err := dns.validate()
+	assert.ErrorContains(t, err, "dns.configFile and dns.hosts are mutually exclusive")
+}
+
+func TestDNS_ValidateConfigFile_WithHostsDisabled(t *testing.T) {
+	tmpFile := createTempCorefile(t, ".:5353 { whoami }")
+
+	dns := DNS{
+		ConfigFile: tmpFile,
+		Hosts: HostsConfig{
+			Status: HostsStatusDisabled,
+		},
+	}
+	assert.NoError(t, dns.validate())
+}
+
+func TestDNS_ValidateConfigFile_EmptyConfigFilePreservesDefault(t *testing.T) {
+	dns := DNS{
+		ConfigFile: "",
+		Hosts: HostsConfig{
+			Status: HostsStatusDisabled,
+		},
+	}
+	assert.NoError(t, dns.validate())
+}
+
+func TestDNS_ValidateConfigFile_NonAbsolutePath(t *testing.T) {
+	dns := DNS{
+		ConfigFile: "relative/path/Corefile",
+		Hosts: HostsConfig{
+			Status: HostsStatusDisabled,
+		},
+	}
+	err := dns.validate()
+	assert.ErrorContains(t, err, "dns config file path must be absolute")
+}
+
+func TestDNS_ValidateConfigFile_NonExistentFile(t *testing.T) {
+	dns := DNS{
+		ConfigFile: "/tmp/nonexistent-corefile-test-12345",
+		Hosts: HostsConfig{
+			Status: HostsStatusDisabled,
+		},
+	}
+	err := dns.validate()
+	assert.ErrorContains(t, err, "does not exist")
+}
+
+func TestDNS_ValidateConfigFile_Directory(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	dns := DNS{
+		ConfigFile: tmpDir,
+		Hosts: HostsConfig{
+			Status: HostsStatusDisabled,
+		},
+	}
+	err := dns.validate()
+	assert.ErrorContains(t, err, "must be a regular file")
+}
+
+func TestDNS_ValidateConfigFile_EmptyFile(t *testing.T) {
+	tmpFile := createTempCorefile(t, "")
+
+	dns := DNS{
+		ConfigFile: tmpFile,
+		Hosts: HostsConfig{
+			Status: HostsStatusDisabled,
+		},
+	}
+	err := dns.validate()
+	assert.ErrorContains(t, err, "is empty")
+}
+
+func TestDNS_ValidateConfigFile_ExceedsSizeLimit(t *testing.T) {
+	tmpDir := t.TempDir()
+	tmpFile := filepath.Join(tmpDir, "Corefile")
+	// 1 MiB + 1 byte
+	data := make([]byte, 1048576+1)
+	require.NoError(t, os.WriteFile(tmpFile, data, 0644))
+
+	dns := DNS{
+		ConfigFile: tmpFile,
+		Hosts: HostsConfig{
+			Status: HostsStatusDisabled,
+		},
+	}
+	err := dns.validate()
+	assert.ErrorContains(t, err, "exceeds 1MiB ConfigMap size limit")
+}
+
+func TestDNS_ValidateConfigFile_ValidFile(t *testing.T) {
+	tmpFile := createTempCorefile(t, ".:5353 {\n    whoami\n    reload\n}\n")
+
+	dns := DNS{
+		ConfigFile: tmpFile,
+		Hosts: HostsConfig{
+			Status: HostsStatusDisabled,
+		},
+	}
+	assert.NoError(t, dns.validate())
+}
+
+func TestDNS_ConfigFile_IncorporatedFromDropIn(t *testing.T) {
+	tmpFile := createTempCorefile(t, ".:5353 {\n    whoami\n    reload\n}\n")
+
+	yamlConfig := fmt.Sprintf("dns:\n  configFile: %s\n", tmpFile)
+	config, err := getActiveConfigFromYAMLDropins([][]byte{[]byte(yamlConfig)})
+	require.NoError(t, err)
+	assert.Equal(t, tmpFile, config.DNS.ConfigFile)
+}
+
+func createTempCorefile(t *testing.T, content string) string {
+	t.Helper()
+	tmpDir := t.TempDir()
+	tmpFile := filepath.Join(tmpDir, "Corefile")
+	require.NoError(t, os.WriteFile(tmpFile, []byte(content), 0644))
+	return tmpFile
+}