dns: support for custom hosts (#512)

* dns: support passing hostresolver custom hosts information to lima

* dns: move custom hosts functionality to network.dns_hosts, and add new cmd line option --dns-host

cmd/start.go

@@ -37,6 +37,7 @@ Run 'colima template' to set the default configurations or 'colima start --edit'
 		"  colima start --cpu 4 --memory 8 --disk 100\n" +
 		"  colima start --arch aarch64\n" +
 		"  colima start --dns 1.1.1.1 --dns 8.8.8.8\n" +
+		"  colima start --dns-host example.com=1.2.3.4\n" +
 		"  colima start --kubernetes --kubernetes-disable=coredns,servicelb,traefik,local-storage,metrics-server",
 	Args: cobra.MaximumNArgs(1),
 	RunE: func(cmd *cobra.Command, args []string) error {
@@ -106,6 +107,7 @@ var startCmdArgs struct {
 		Edit             bool
 		Editor           string
 		ActivateRuntime  bool
+		DNSHosts         []string
 	}
 }
 
@@ -168,7 +170,25 @@ func init() {
 	startCmd.Flags().StringToStringVar(&startCmdArgs.Env, "env", nil, "environment variables for the VM")
 
 	// dns
-	startCmd.Flags().IPSliceVarP(&startCmdArgs.Network.DNS, "dns", "n", nil, "DNS servers for the VM")
+	startCmd.Flags().IPSliceVarP(&startCmdArgs.Network.DNSResolvers, "dns", "n", nil, "DNSResolvers servers for the VM")
+	startCmd.Flags().StringSliceVarP(&startCmdArgs.Flags.DNSHosts, "dns-host", "", nil, "Custom DNS names to provide to resolver")
+}
+
+func dnsHostsFromFlag(hosts []string) map[string]string {
+	mapping := make(map[string]string)
+
+	for _, h := range hosts {
+		str := strings.SplitN(h, "=", 2)
+		if len(str) != 2 {
+			log.Warnf("unable to parse custom dns host: %v, skipping\n", h)
+			continue
+		}
+		src := str[0]
+		target := str[1]
+
+		mapping[src] = target
+	}
+	return mapping
 }
 
 // mountsFromFlag converts mounts from cli flag format to config file format
@@ -210,6 +230,7 @@ func prepareConfig(cmd *cobra.Command) {
 
 	// convert cli to config file format
 	startCmdArgs.Mounts = mountsFromFlag(startCmdArgs.Flags.Mounts)
+	startCmdArgs.Network.DNSHosts = dnsHostsFromFlag(startCmdArgs.Flags.DNSHosts)
 	startCmdArgs.ActivateRuntime = &startCmdArgs.Flags.ActivateRuntime
 
 	// handle macOS virtualization.framework transition
@@ -280,7 +301,10 @@ func prepareConfig(cmd *cobra.Command) {
 		startCmdArgs.SSHConfig = current.SSHConfig
 	}
 	if !cmd.Flag("dns").Changed {
-		startCmdArgs.Network.DNS = current.Network.DNS
+		startCmdArgs.Network.DNSResolvers = current.Network.DNSResolvers
+	}
+	if !cmd.Flag("dns-host").Changed {
+		startCmdArgs.Network.DNSHosts = current.Network.DNSHosts
 	}
 	if !cmd.Flag("env").Changed {
 		startCmdArgs.Env = current.Env

config/config.go

@@ -115,8 +115,9 @@ type Kubernetes struct {
 
 // Network is VM network configuration
 type Network struct {
-	Address bool     `yaml:"address"`
-	DNS     []net.IP `yaml:"dns"`
+	Address      bool              `yaml:"address"`
+	DNSResolvers []net.IP          `yaml:"dns"`
+	DNSHosts     map[string]string `yaml:"dns_hosts"`
 }
 
 // Mount is volume mount

embedded/defaults/colima.yaml

@@ -61,6 +61,12 @@ network:
   # Default: []
   dns: []
 
+  # DNS hostnames to resolve to custom targets using the internal Lima resolver.
+  # This setting has no effect if a custom DNS resolver list is supplied above.
+  # It does not configure the /etc/hosts files of any machine or container.
+  dns_hosts:
+    host.docker.internal: host.lima.internal
+
 # ===================================================================== #
 # ADVANCED CONFIGURATION
 # ===================================================================== #
@@ -168,4 +174,4 @@ mounts: []
 #   ANOTHER_KEY: another value
 #
 # Default: {}
-env: {}
+env: {}

environment/vm/lima/yaml.go

@@ -67,10 +67,15 @@ func newConf(ctx context.Context, conf config.Config) (l Config, err error) {
 	l.SSH = SSH{LocalPort: 0, LoadDotSSHPubKeys: false, ForwardAgent: conf.ForwardAgent}
 	l.Containerd = Containerd{System: false, User: false}
 
-	l.DNS = conf.Network.DNS
-	l.HostResolver.Enabled = len(l.DNS) == 0
-	l.HostResolver.Hosts = map[string]string{
-		"host.docker.internal": "host.lima.internal",
+	l.DNS = conf.Network.DNSResolvers
+	l.HostResolver.Enabled = len(conf.Network.DNSResolvers) == 0
+	l.HostResolver.Hosts = conf.Network.DNSHosts
+	if l.HostResolver.Hosts == nil {
+		l.HostResolver.Hosts = make(map[string]string)
+	}
+
+	if _, ok := l.HostResolver.Hosts["host.docker.internal"]; !ok {
+		l.HostResolver.Hosts["host.docker.internal"] = "host.lima.internal"
 	}
 
 	l.Env = conf.Env

util/yamlutil/yaml_test.go

@@ -12,7 +12,7 @@ import (
 func Test_encode_Docker(t *testing.T) {
 	conf := config.Config{
 		Docker:     map[string]any{"insecure-registries": []any{"127.0.0.1"}},
-		Network:    config.Network{DNS: []net.IP{net.ParseIP("1.1.1.1")}},
+		Network:    config.Network{DNSResolvers: []net.IP{net.ParseIP("1.1.1.1")}},
 		Kubernetes: config.Kubernetes{Disable: []string{"treafik"}},
 	}