diff --git a/go/cli/commands/build.go b/go/cli/commands/build.go
index 48944e15c..10ff9dafc 100644
--- a/go/cli/commands/build.go
+++ b/go/cli/commands/build.go
@@ -15,14 +15,12 @@
 package commands
 
 import (
-	"bytes"
 	"context"
 	"embed"
 	"errors"
 	"fmt"
 	"os"
 	"os/exec"
-	"strings"
 
 	"github.com/heroku/color"
 	"github.com/spf13/cobra"
@@ -30,80 +28,120 @@ import (
 
 //go:embed embed/Dockerfile
 var f embed.FS
+var execCmdFn = execCmd
+var execLookPathFn = exec.LookPath
 
 const (
-	ImageTag              = "function:latest"
+	// Builder Type
+	Ko     = "ko"
+	Docker = "docker"
+
+	// Docker constant variables
+	Image                 = "function:latest"
 	DockerfilePath        = "Dockerfile"
-	builtinDockerfilePath = "embed/Dockerfile"
+	BuiltinDockerfilePath = "embed/Dockerfile"
+
+	// Ko constant variables
+	KoDockerRepoEnvVar = "KO_DOCKER_REPO"
+	KoLocalRepo        = "ko.local"
 )
 
-func NewBuildCmd(ctx context.Context) *cobra.Command {
+func NewBuildRunner(ctx context.Context) *BuildRunner {
 	r := &BuildRunner{
-		ctx: ctx,
+		ctx:    ctx,
+		Ko:     &KoBuilder{},
+		Docker: &DockerBuilder{},
 	}
 	r.Command = &cobra.Command{
-		Use:     "build",
-		Short:   "build the KRM function as a docker image",
-		PreRunE: r.PreRunE,
-		RunE:    r.RunE,
-	}
-	r.Command.Flags().StringVarP(&r.Tag, "tag", "t", ImageTag,
-		"the docker image tag")
-	r.Command.Flags().StringVarP(&r.DockerfilePath, "file", "f", "",
-		"Name of the Dockerfile. If not given, using a default builtin Dockerfile")
-	return r.Command
+		Use:   "build",
+		Short: "build your KRM function to a container image",
+		RunE:  r.RunE,
+	}
+	r.Command.Flags().StringVarP(&r.BuilderType, "builder", "b", Ko,
+		"the image builder. `ko` is the default builder, which requires `go build`; `docker` is accepted, and "+
+			" requires you to have docker installed and running")
+	r.Command.Flags().StringVarP(&r.Docker.Image, "image", "i", Image,
+		fmt.Sprintf("the image (with tag), default to %v", Image))
+	r.Command.Flags().StringVarP(&r.Docker.DockerfilePath, "dockerfile", "f", "",
+		"path to the Dockerfile. If not given, using a default builtin Dockerfile")
+	r.Command.Flags().StringVarP(&r.Ko.Repo, "repo", "r", "",
+		"the image repo. default to ko.local")
+	r.Command.Flags().StringVarP(&r.Ko.Tag, "tag", "t", "latest",
+		"the ko image tag")
+	// TODO: Docker CLI uses `--tag` flag to refer to "image:tag", which could be confusing but broadly accepted.
+	// We should better guide users on how to use "tag" and "image" flags for kfn.
+	// Here we use "tag" for ko <tag> (same as `ko build --tag`) and "image" for docker <image:tag> (same as `docker build --tag`)
+	return r
 }
 
 type BuildRunner struct {
 	ctx     context.Context
 	Command *cobra.Command
 
-	Tag            string
+	BuilderType string
+	Tag         string
+	Ko          *KoBuilder
+	Docker      *DockerBuilder
+}
+
+type Builder interface {
+	Build() error
+	Validate() error
+}
+
+type DockerBuilder struct {
+	Image          string
 	DockerfilePath string
 }
 
-func (r *BuildRunner) PreRunE(cmd *cobra.Command, args []string) error {
-	if err := r.requireDocker(); err != nil {
-		return err
-	}
-	if !r.dockerfileExist() {
-		err := r.createDockerfile()
-		if err != nil {
-			return err
-		}
-	}
-	return nil
+type KoBuilder struct {
+	Repo string
+	Tag  string
 }
 
 func (r *BuildRunner) RunE(cmd *cobra.Command, args []string) error {
-	return r.runDockerBuild()
+	var builder Builder
+	switch r.BuilderType {
+	case Docker:
+		builder = r.Docker
+	case Ko:
+		builder = r.Ko
+	}
+	if err := builder.Validate(); err != nil {
+		return err
+	}
+	return builder.Build()
 }
 
-func (r *BuildRunner) runDockerBuild() error {
-	args := []string{"build", ".", "-f", r.DockerfilePath, "--tag", r.Tag}
-	cmd := exec.Command("docker", args...)
-	var out, errout bytes.Buffer
-	cmd.Stdout = &out
-	cmd.Stderr = &errout
-	err := cmd.Run()
+func (r *DockerBuilder) Build() error {
+	args := []string{"build", ".", "-f", r.DockerfilePath, "--tag", r.Image}
+	err := execCmdFn(nil, "docker", args...)
 	if err != nil {
-		color.Red(strings.TrimSpace(errout.String()))
 		return err
 	}
-	color.Green(out.String())
-	color.Green("Image %v builds successfully. Now you can publish the image", r.Tag)
+	color.Green("Image %v built successfully. Now you can publish the image", r.Image)
 	return nil
 }
 
-func (r *BuildRunner) requireDocker() error {
-	_, err := exec.LookPath("docker")
+func (r *DockerBuilder) Validate() error {
+	if err := r.validateDockerInstalled(); err != nil {
+		return err
+	}
+	if r.dockerfileExists() {
+		return nil
+	}
+	return r.createDockerfile()
+}
+
+func (r *DockerBuilder) validateDockerInstalled() error {
+	_, err := execLookPathFn("docker")
 	if err != nil {
 		return fmt.Errorf("kfn requires that `docker` is installed and on the PATH")
 	}
 	return nil
 }
 
-func (r *BuildRunner) dockerfileExist() bool {
+func (r *DockerBuilder) dockerfileExists() bool {
 	if r.DockerfilePath == "" {
 		r.DockerfilePath = DockerfilePath
 	}
@@ -114,14 +152,80 @@ func (r *BuildRunner) dockerfileExist() bool {
 	return true
 }
 
-func (r *BuildRunner) createDockerfile() error {
-	dockerfileContent, err := f.ReadFile(builtinDockerfilePath)
+func (r *DockerBuilder) createDockerfile() error {
+	dockerfileContent, err := f.ReadFile(BuiltinDockerfilePath)
 	if err != nil {
 		return err
 	}
-	if err := os.WriteFile(DockerfilePath, dockerfileContent, 0644); err != nil {
+	if err = os.WriteFile(DockerfilePath, dockerfileContent, 0644); err != nil {
 		return err
 	}
-	color.Green("created Dockerfile")
+	fmt.Println("created Dockerfile")
 	return nil
 }
+
+func (r *KoBuilder) GuaranteeKoInstalled() error {
+	_, err := execLookPathFn("ko")
+	if err == nil {
+		return nil
+	}
+	gobin := os.Getenv("GOBIN")
+	if gobin == "" && os.Getenv("GOPATH") != "" {
+		gobin = os.Getenv("GOPATH") + "/bin"
+	}
+	if gobin == "" && os.Getenv("HOME") != "" {
+		gobin = os.Getenv("HOME") + "/go/bin"
+	}
+	var envs []string
+	if gobin != "" {
+		envs = []string{"GOBIN" + "=" + gobin}
+	}
+	if err = execCmdFn(envs, "go", "install", "github.com/google/ko@latest"); err != nil {
+		return err
+	}
+	fmt.Println("successfully installed ko")
+	return nil
+}
+func (r *KoBuilder) Build() error {
+	args := []string{"build", "-B", "--tags", r.Tag}
+	envs := []string{KoDockerRepoEnvVar + "=" + r.Repo}
+	err := execCmdFn(envs, "ko", args...)
+	if err != nil {
+		return err
+	}
+
+	if r.Repo == KoLocalRepo {
+		color.Green("Image built successfully. Now you can publish the image")
+	} else {
+		color.Green("Image built and pushed successfully")
+	}
+	return nil
+}
+
+func (r *KoBuilder) Validate() error {
+	if err := r.GuaranteeKoInstalled(); err != nil {
+		return err
+	}
+	// Find KO_DOCKER_REPO value from multiple places for `ko build`.
+	if r.Repo != "" {
+		return nil
+	}
+	if repo, ok := os.LookupEnv(KoDockerRepoEnvVar); ok {
+		r.Repo = repo
+		return nil
+	}
+	r.Repo = "ko.local"
+	return nil
+}
+
+func execCmd(envs []string, name string, args ...string) error {
+	cmd := exec.Command(name, args...)
+	if len(envs) != 0 {
+		cmd.Env = os.Environ()
+		cmd.Env = append(cmd.Env, envs...)
+	}
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	err := cmd.Run()
+	return err
+}
diff --git a/go/cli/commands/build_test.go b/go/cli/commands/build_test.go
new file mode 100644
index 000000000..71f0782c1
--- /dev/null
+++ b/go/cli/commands/build_test.go
@@ -0,0 +1,155 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package commands
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBuild(t *testing.T) {
+	testcases := map[string]struct {
+		args []string
+		// expected args is key, and expected return is value
+		cmdExpected []string
+		// expected env var is key, and existence is value
+		lookPathExpected map[string]bool
+		expectedError    string
+	}{
+		"default build is ko, ko already exists": {
+			args: []string{""},
+			cmdExpected: []string{
+				"KO_DOCKER_REPO=ko.local ko build -B --tags latest",
+			},
+			lookPathExpected: map[string]bool{
+				"ko": true,
+			},
+		},
+		"default build is ko, ko not exists": {
+			args: []string{""},
+			cmdExpected: []string{
+				"go install github.com/google/ko@latest",
+				"KO_DOCKER_REPO=ko.local ko build -B --tags latest",
+			},
+			lookPathExpected: map[string]bool{
+				"ko": false,
+			},
+		},
+		"ko as builder, specify repo": {
+			args: []string{"--repo=gcr.io/test"},
+			cmdExpected: []string{
+				"KO_DOCKER_REPO=gcr.io/test ko build -B --tags latest",
+			},
+			lookPathExpected: map[string]bool{
+				"ko": true,
+			},
+		},
+		"ko as builder, specify tag": {
+			args: []string{"--repo=gcr.io/test", "--tag=v1"},
+			cmdExpected: []string{
+				"KO_DOCKER_REPO=gcr.io/test ko build -B --tags v1",
+			},
+			lookPathExpected: map[string]bool{
+				"ko": true,
+			},
+		},
+		"docker as builder, docker not exists": {
+			args: []string{"--builder=docker"},
+			lookPathExpected: map[string]bool{
+				"docker": false,
+			},
+			expectedError: "kfn requires that `docker` is installed and on the PATH",
+		},
+		"docker as builder, docker exists": {
+			args: []string{"--builder=docker"},
+			cmdExpected: []string{
+				"docker build . -f Dockerfile --tag function:latest",
+			},
+			lookPathExpected: map[string]bool{
+				"docker": true,
+			},
+		},
+		"docker as builder, specify dockerfile": {
+			args: []string{"--builder=docker", "--dockerfile=tmp/Dockerfile"},
+			cmdExpected: []string{
+				"docker build . -f tmp/Dockerfile --tag function:latest",
+			},
+			lookPathExpected: map[string]bool{
+				"docker": true,
+			},
+		},
+		"docker as builder, specify image": {
+			args: []string{"--builder=docker", "--image=dockertest:latest", "--dockerfile=tmp/Dockerfile"},
+			cmdExpected: []string{
+				"docker build . -f tmp/Dockerfile --tag dockertest:latest",
+			},
+			lookPathExpected: map[string]bool{
+				"docker": true,
+			},
+		},
+	}
+	for name, test := range testcases {
+		r := NewBuildRunner(context.TODO())
+		execCmdFn = func(envs []string, name string, args ...string) error {
+			fakeExecCmd(t, test.cmdExpected, envs, name, args...)
+			return nil
+		}
+		execLookPathFn = func(file string) (string, error) {
+			return "", fakeExecLookPath(t, test.lookPathExpected, file)
+		}
+		r.Command.SetArgs(test.args)
+		err := r.Command.Execute()
+		if test.expectedError == "" {
+			if err != nil {
+				t.Errorf("%v failed. got error: %v", name, err)
+			}
+		} else {
+			assert.EqualError(t, err, test.expectedError)
+		}
+		os.Remove("Dockerfile")
+	}
+}
+
+func fakeExecCmd(t *testing.T, expectedArgsAndReturns []string, envs []string, name string, args ...string) {
+	var c []string
+	if name != "go" {
+		c = append(c, envs...)
+	}
+	c = append(c, name)
+	c = append(c, args...)
+	command := strings.Join(c, " ")
+	for _, expected := range expectedArgsAndReturns {
+		if expected == command {
+			return
+		}
+	}
+	t.Fatalf("unexpected command run %v", command)
+}
+
+func fakeExecLookPath(t *testing.T, expectedlookPath map[string]bool, name string) error {
+	val, ok := expectedlookPath[name]
+	if !ok {
+		t.Fatalf("unexpected env var check %v", name)
+	}
+	if val {
+		return nil
+	}
+	return fmt.Errorf("env var not exists")
+}
diff --git a/go/cli/commands/init.go b/go/cli/commands/init.go
index 71d9f7216..b89c6c015 100644
--- a/go/cli/commands/init.go
+++ b/go/cli/commands/init.go
@@ -29,7 +29,7 @@ const (
 	DefaultPkgName = "function"
 )
 
-func NewInitCmd(ctx context.Context) *cobra.Command {
+func NewInitRunner(ctx context.Context) *InitRunner {
 	r := &InitRunner{
 		ctx: ctx,
 	}
@@ -41,7 +41,7 @@ func NewInitCmd(ctx context.Context) *cobra.Command {
 	}
 	r.Command.Flags().StringVarP(&r.FnPkgPath, "fnPkg", "", DefaultFnPkg,
 		"a kpt package that contains a basic KRM function source code to get start")
-	return r.Command
+	return r
 }
 
 // InitRunner initializes a KRM function project from a scaffolded `kpt pkg`.
diff --git a/go/cli/go.mod b/go/cli/go.mod
index 93e954d70..39d7a90a2 100644
--- a/go/cli/go.mod
+++ b/go/cli/go.mod
@@ -5,12 +5,16 @@ go 1.19
 require (
 	github.com/heroku/color v0.0.6
 	github.com/spf13/cobra v1.6.1
+	github.com/stretchr/testify v1.8.1
 )
 
 require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/inconshreveable/mousetrap v1.0.1 // indirect
 	github.com/mattn/go-colorable v0.1.2 // indirect
 	github.com/mattn/go-isatty v0.0.8 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
 	golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
diff --git a/go/cli/go.sum b/go/cli/go.sum
index 6a367ac31..29d9662f7 100644
--- a/go/cli/go.sum
+++ b/go/cli/go.sum
@@ -1,4 +1,7 @@
 github.com/cpuguy83/go-md2man/v2 v2.0.2/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46tRHOmNcaadrF8o=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/heroku/color v0.0.6 h1:UTFFMrmMLFcL3OweqP1lAdp8i1y/9oHqkeHjQ/b/Ny0=
 github.com/heroku/color v0.0.6/go.mod h1:ZBvOcx7cTF2QKOv4LbmoBtNl5uB17qWxGuzZrsi1wLU=
 github.com/inconshreveable/mousetrap v1.0.1 h1:U3uMjPSQEBMNp1lFxmllqCPM6P5u/Xq7Pgzkat/bFNc=
@@ -7,13 +10,25 @@ github.com/mattn/go-colorable v0.1.2 h1:/bC9yWikZXAL9uJdulbSfyVNIR3n3trXl+v8+1sx
 github.com/mattn/go-colorable v0.1.2/go.mod h1:U0ppj6V5qS13XJ6of8GYAs25YV2eR4EVcfRqFIhoBtE=
 github.com/mattn/go-isatty v0.0.8 h1:HLtExJ+uU2HOZ+wI0Tt5DtUDrx8yhUqDcp7fYERX4CE=
 github.com/mattn/go-isatty v0.0.8/go.mod h1:Iq45c/XA43vh69/j3iqttzPXn0bhXyGjM0Hdxcsrc5s=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/spf13/cobra v1.6.1 h1:o94oiPyS4KD1mPy2fmcYYHHfCxLqYjJOhGsCHFZtEzA=
 github.com/spf13/cobra v1.6.1/go.mod h1:IOw/AERYS7UzyrGinqmz6HLUo219MORXGxhbaJUqzrY=
 github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
 github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
+github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
 golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a h1:dGzPydgVsqGcTRVwiLJ1jVbufYwmzD3LfVPLKsKg+0k=
 golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/go/cli/main.go b/go/cli/main.go
index a3b43a51d..6fd4dc53c 100644
--- a/go/cli/main.go
+++ b/go/cli/main.go
@@ -29,8 +29,8 @@ func main() {
 		Short: "a CLI tool to edit your own KRM functions with ease",
 	}
 	ctx := context.Background()
-	cmd.AddCommand(commands.NewInitCmd(ctx))
-	cmd.AddCommand(commands.NewBuildCmd(ctx))
+	cmd.AddCommand(commands.NewInitRunner(ctx).Command)
+	cmd.AddCommand(commands.NewBuildRunner(ctx).Command)
 	err = cmd.Execute()
 	if err != nil {
 		os.Exit(1)