@@ -3,6 +3,7 @@ package buildkit

 import (

 	"context"

 	"io"

+	"net"

 	"strings"

 	"sync"

 	"time"

@@ -244,6 +245,12 @@ func (b *Builder) Build(ctx context.Context, opt backend.BuildConfig) (*builder.

 		return nil, errors.Errorf("network mode %q not supported by buildkit", opt.Options.NetworkMode)

 	}

+	extraHosts, err := toBuildkitExtraHosts(opt.Options.ExtraHosts)

+	if err != nil {

+		return nil, err

+	}

+	frontendAttrs["add-hosts"] = extraHosts

+

 	exporterAttrs := map[string]string{}

 	if len(opt.Options.Tags) > 0 {

@@ -444,3 +451,19 @@ func (j *buildJob) SetUpload(ctx context.Context, rc io.ReadCloser) error {

 		return fn(rc)

 	}

 }

+

+// toBuildkitExtraHosts converts hosts from docker key:value format to buildkit's csv format

+func toBuildkitExtraHosts(inp []string) (string, error) {

+	if len(inp) == 0 {

+		return "", nil

+	}

+	hosts := make([]string, 0, len(inp))

+	for _, h := range inp {

+		parts := strings.Split(h, ":")

+		if len(parts) != 2 || parts[0] == "" || net.ParseIP(parts[1]) == nil {

+			return "", errors.Errorf("invalid host %s", h)

+		}

+		hosts = append(hosts, parts[0]+"="+parts[1])

+	}

+	return strings.Join(hosts, ","), nil

+}