feat: add --add-host flag to customize host-to-IP mapping in /etc/hosts

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

README.md

@@ -166,6 +166,7 @@ Usage:
 
 Flags:
       --append-to-cmdline string   Extra kernel cmdline arguments to append to the generated one
+      --add-host strings           Add a custom host-to-IP mapping (host:ip) to the /etc/hosts file in the generated image
       --boot-fs string             Filesystem to use for the boot partition, ext4 or fat32
       --boot-size uint             Size of the boot partition in MB (default 100)
       --bootloader string          Bootloader to use: syslinux, grub, grub-bios, grub-efi, defaults to syslinux on amd64 and grub-efi on arm64
@@ -327,6 +328,7 @@ Usage:
 
 Flags:
       --append-to-cmdline string   Extra kernel cmdline arguments to append to the generated one
+      --add-host strings           Add a custom host-to-IP mapping (host:ip) to the /etc/hosts file in the generated image
       --boot-fs string             Filesystem to use for the boot partition, ext4 or fat32
       --boot-size uint             Size of the boot partition in MB (default 100)
       --bootloader string          Bootloader to use: syslinux, grub, grub-bios, grub-efi, defaults to syslinux on amd64 and grub-efi on arm64

builder.go

@@ -87,9 +87,10 @@ type builder struct {
 	hostname  string
 	dns       []string
 	dnsSearch []string
+	hosts     string
 }
 
-func NewBuilder(ctx context.Context, workdir, imgTag, disk string, size uint64, osRelease OSRelease, format string, cmdLineExtra string, splitBoot bool, bootFS BootFS, bootSize uint64, luksPassword string, bootLoader string, platform, hostname string, dns, dnsSearch []string) (Builder, error) {
+func NewBuilder(ctx context.Context, workdir, imgTag, disk string, size uint64, osRelease OSRelease, format string, cmdLineExtra string, splitBoot bool, bootFS BootFS, bootSize uint64, luksPassword string, bootLoader string, platform, hostname string, dns, dnsSearch []string, extraHosts map[string]string) (Builder, error) {
 	var arch string
 	switch platform {
 	case "linux/amd64":
@@ -189,6 +190,10 @@ func NewBuilder(ctx context.Context, workdir, imgTag, disk string, size uint64,
 	if len(dns) == 0 {
 		dns = []string{"8.8.8.8"}
 	}
+	hosts := hosts
+	for k, v := range extraHosts {
+		hosts += fmt.Sprintf("%s %s\n", v, k)
+	}
 	b := &builder{
 		osRelease:    osRelease,
 		config:       config,
@@ -208,6 +213,7 @@ func NewBuilder(ctx context.Context, workdir, imgTag, disk string, size uint64,
 		hostname:     hostname,
 		dns:          dns,
 		dnsSearch:    dnsSearch,
+		hosts:        hosts,
 	}
 	if err := b.checkDependencies(); err != nil {
 		return nil, err
@@ -428,7 +434,7 @@ func (b *builder) setupRootFS(ctx context.Context) (err error) {
 	if err := b.chWriteFile("/etc/hostname", b.hostname+"\n", perm); err != nil {
 		return err
 	}
-	if err := b.chWriteFileIfNotExist("/etc/hosts", hosts, perm); err != nil {
+	if err := b.chWriteFile("/etc/hosts", b.hosts, perm); err != nil {
 		return err
 	}
 	// TODO(adphi): is it the righ fix ?

cmd/d2vm/build.go

@@ -113,6 +113,7 @@ var (
 				d2vm.WithHostname(hostname),
 				d2vm.WithDNS(dns),
 				d2vm.WithDNSSearch(dnsSearch),
+				d2vm.WithExtraHosts(extraHosts),
 			); err != nil {
 				return err
 			}

cmd/d2vm/convert.go

@@ -94,6 +94,7 @@ var (
 				d2vm.WithHostname(hostname),
 				d2vm.WithDNS(dns),
 				d2vm.WithDNSSearch(dnsSearch),
+				d2vm.WithExtraHosts(extraHosts),
 			); err != nil {
 				return err
 			}

cmd/d2vm/flags.go

@@ -48,9 +48,12 @@ var (
 	hostname  string
 	dns       []string
 	dnsSearch []string
+	hosts     []string
+
+	extraHosts map[string]string
 )
 
-func validateFlags() error {
+func validateFlags() (err error) {
 	switch platform {
 	case "linux/amd64":
 		if bootloader == "" {
@@ -98,6 +101,10 @@ func validateFlags() error {
 			return fmt.Errorf("%s already exists", output)
 		}
 	}
+	extraHosts, err = validateHosts(hosts...)
+	if err != nil {
+		return fmt.Errorf("invalid --add-host value: %w", err)
+	}
 	return nil
 }
 
@@ -123,5 +130,19 @@ func buildFlags() *pflag.FlagSet {
 	flags.StringVar(&hostname, "hostname", "localhost", "Hostname to set in the generated image")
 	flags.StringSliceVar(&dns, "dns", []string{}, "DNS servers to set in the generated image")
 	flags.StringSliceVar(&dnsSearch, "dns-search", []string{}, "DNS search domains to set in the generated image")
+	flags.StringSliceVar(&hosts, "add-host", []string{}, "Add a custom host-to-IP mapping (host:ip) to the /etc/hosts file in the generated image")
 	return flags
 }
+
+func validateHosts(vals ...string) (map[string]string, error) {
+	out := make(map[string]string)
+	for _, val := range vals {
+		// allow for IPv6 addresses in extra hosts by only splitting on first ":"
+		k, v, ok := strings.Cut(val, ":")
+		if !ok || k == "" {
+			return nil, fmt.Errorf("bad format for add-host: %q", val)
+		}
+		out[k] = v
+	}
+	return out, nil
+}

convert.go

@@ -88,7 +88,7 @@ func Convert(ctx context.Context, img string, opts ...ConvertOption) error {
 	if format == "" {
 		format = "raw"
 	}
-	b, err := NewBuilder(ctx, tmpPath, imgUUID, "", o.size, r, format, o.cmdLineExtra, o.splitBoot, o.bootFS, o.bootSize, o.luksPassword, o.bootLoader, o.platform, o.hostname, o.dns, o.dnsSearch)
+	b, err := NewBuilder(ctx, tmpPath, imgUUID, "", o.size, r, format, o.cmdLineExtra, o.splitBoot, o.bootFS, o.bootSize, o.luksPassword, o.bootLoader, o.platform, o.hostname, o.dns, o.dnsSearch, o.hosts)
 	if err != nil {
 		return err
 	}

convert_options.go

@@ -38,6 +38,7 @@ type convertOptions struct {
 	hostname  string
 	dns       []string
 	dnsSearch []string
+	hosts     map[string]string
 }
 
 func (o *convertOptions) hasGrubBIOS() bool {
@@ -149,3 +150,9 @@ func WithDNSSearch(dnsSearch []string) ConvertOption {
 		o.dnsSearch = dnsSearch
 	}
 }
+
+func WithExtraHosts(hosts map[string]string) ConvertOption {
+	return func(o *convertOptions) {
+		o.hosts = hosts
+	}
+}

docs/content/reference/d2vm_build.md

@@ -9,6 +9,7 @@ d2vm build [context directory] [flags]
 ### Options
 
 ```
+      --add-host strings           Add a custom host-to-IP mapping (host:ip) to the /etc/hosts file in the generated image
       --append-to-cmdline string   Extra kernel cmdline arguments to append to the generated one
       --boot-fs string             Filesystem to use for the boot partition, ext4 or fat32
       --boot-size uint             Size of the boot partition in MB (default 100)

docs/content/reference/d2vm_convert.md

@@ -9,6 +9,7 @@ d2vm convert [docker image] [flags]
 ### Options
 
 ```
+      --add-host strings           Add a custom host-to-IP mapping (host:ip) to the /etc/hosts file in the generated image
       --append-to-cmdline string   Extra kernel cmdline arguments to append to the generated one
       --boot-fs string             Filesystem to use for the boot partition, ext4 or fat32
       --boot-size uint             Size of the boot partition in MB (default 100)