cmd/build: Add buildah support (#1311)

**Description of the change:**
This PR adds buildah support.

**Motivation for the change:**
operator-sdk should support building image by using buildah. 
There is an existing discussion for motivation in #563 .

CHANGELOG.md

@@ -2,11 +2,14 @@
 
 ### Added
 
+- New option for [`operator-sdk build --image-builder`](https://github.com/operator-framework/operator-sdk/blob/master/doc/sdk-cli-reference.md#build), which can be used to specify which image builder to use. Adds support for [buildah](https://github.com/containers/buildah/). ([#1311](https://github.com/operator-framework/operator-sdk/pull/1311))
+
 ### Changed
 
 - When Helm operator projects are created, the SDK now generates RBAC rules in `deploy/role.yaml` based on the chart's default manifest. ([#1188](https://github.com/operator-framework/operator-sdk/pull/1188))
 - When debug level is 3 or higher, we will set the klog verbosity to that level. ([#1322](https://github.com/operator-framework/operator-sdk/pull/1322))
 - Relaxed requirements for groups in new project API's. Groups passed to [`operator-sdk add api`](https://github.com/operator-framework/operator-sdk/blob/master/doc/sdk-cli-reference.md#api)'s `--api-version` flag can now have no subdomains, ex `core/v1`. See ([#1191](https://github.com/operator-framework/operator-sdk/issues/1191)) for discussion. ([#1313](https://github.com/operator-framework/operator-sdk/pull/1313))
+- Renamed `--docker-build-args` option to `--image-build-args` option for `build` subcommand, because this option can now be shared with other image build tools than docker when `--image-builder` option is specified. ([#1311](https://github.com/operator-framework/operator-sdk/pull/1311))
 
 ### Deprecated
 

cmd/operator-sdk/build/cmd.go

@@ -38,7 +38,8 @@ var (
 	namespacedManBuild string
 	testLocationBuild  string
 	enableTests        bool
-	dockerBuildArgs    string
+	imageBuildArgs     string
+	imageBuilder       string
 )
 
 func NewCmd() *cobra.Command {
@@ -62,7 +63,8 @@ For example:
 	buildCmd.Flags().BoolVar(&enableTests, "enable-tests", false, "Enable in-cluster testing by adding test binary to the image")
 	buildCmd.Flags().StringVar(&testLocationBuild, "test-location", "./test/e2e", "Location of tests")
 	buildCmd.Flags().StringVar(&namespacedManBuild, "namespaced-manifest", "deploy/operator.yaml", "Path of namespaced resources manifest for tests")
-	buildCmd.Flags().StringVar(&dockerBuildArgs, "docker-build-args", "", "Extra docker build arguments as one string such as \"--build-arg https_proxy=$https_proxy\"")
+	buildCmd.Flags().StringVar(&imageBuildArgs, "image-build-args", "", "Extra image build arguments as one string such as \"--build-arg https_proxy=$https_proxy\"")
+	buildCmd.Flags().StringVar(&imageBuilder, "image-builder", "docker", "Tool to build OCI images. One of: [docker, buildah]")
 	return buildCmd
 }
 
@@ -141,6 +143,29 @@ func verifyTestManifest(image string) error {
 	return nil
 }
 
+func createBuildCommand(imageBuilder, context, dockerFile, image string, imageBuildArgs ...string) (*exec.Cmd, error) {
+	var args []string
+	switch imageBuilder {
+	case "docker":
+		args = append(args, "build", "-f", dockerFile, "-t", image)
+	case "buildah":
+		args = append(args, "bud", "--format=docker", "-f", dockerFile, "-t", image)
+	default:
+		return nil, fmt.Errorf("%s is not supported image builder", imageBuilder)
+	}
+
+	for _, bargs := range imageBuildArgs {
+		if bargs != "" {
+			splitArgs := strings.Fields(bargs)
+			args = append(args, splitArgs...)
+		}
+	}
+
+	args = append(args, context)
+
+	return exec.Command(imageBuilder, args...), nil
+}
+
 func buildFunc(cmd *cobra.Command, args []string) error {
 	if len(args) != 1 {
 		return fmt.Errorf("command %s requires exactly one argument", cmd.CommandPath())
@@ -170,17 +195,14 @@ func buildFunc(cmd *cobra.Command, args []string) error {
 		baseImageName += "-intermediate"
 	}
 
-	log.Infof("Building Docker image %s", baseImageName)
-
-	dbArgs := []string{"build", ".", "-f", "build/Dockerfile", "-t", baseImageName}
+	log.Infof("Building OCI image %s", baseImageName)
 
-	if dockerBuildArgs != "" {
-		splitArgs := strings.Fields(dockerBuildArgs)
-		dbArgs = append(dbArgs, splitArgs...)
+	buildCmd, err := createBuildCommand(imageBuilder, ".", "build/Dockerfile", baseImageName, imageBuildArgs)
+	if err != nil {
+		return err
 	}
 
-	dbcmd := exec.Command("docker", dbArgs...)
-	if err := projutil.ExecCmd(dbcmd); err != nil {
+	if err := projutil.ExecCmd(buildCmd); err != nil {
 		if enableTests {
 			return fmt.Errorf("failed to output intermediate image %s: (%v)", image, err)
 		}
@@ -232,17 +254,15 @@ func buildFunc(cmd *cobra.Command, args []string) error {
 			}
 		}
 
-		log.Infof("Building test Docker image %s", image)
-
-		testDbArgs := []string{"build", ".", "-f", testDockerfile, "-t", image, "--build-arg", "NAMESPACEDMAN=" + namespacedManBuild, "--build-arg", "BASEIMAGE=" + baseImageName}
+		log.Infof("Building test OCI image %s", image)
 
-		if dockerBuildArgs != "" {
-			splitArgs := strings.Fields(dockerBuildArgs)
-			testDbArgs = append(testDbArgs, splitArgs...)
+		testImageBuildArgs := fmt.Sprintf("--build-arg NAMESPACEDMAN=%s --build-arg BASEIMAGE=%s", namespacedManBuild, baseImageName)
+		testBuildCmd, err := createBuildCommand(imageBuilder, ".", testDockerfile, image, imageBuildArgs, testImageBuildArgs)
+		if err != nil {
+			return err
 		}
 
-		testDbcmd := exec.Command("docker", testDbArgs...)
-		if err := projutil.ExecCmd(testDbcmd); err != nil {
+		if err := projutil.ExecCmd(testBuildCmd); err != nil {
 			return fmt.Errorf("failed to output test image %s: (%v)", image, err)
 		}
 		// Check image name of deployments in namespaced manifest

doc/sdk-cli-reference.md

@@ -16,7 +16,8 @@ Usage:
 * `--enable-tests` - enable in-cluster testing by adding test binary to the image
 * `--namespaced-manifest` string - path of namespaced resources manifest for tests (default "deploy/operator.yaml")
 * `--test-location` string - location of tests (default "./test/e2e")
-* `--docker-build-args` string - extra, optional docker build arguments as one string such as `"--build-arg https_proxy=$https_proxy"` (default "")
+* `--image-build-args` string - extra, optional image build arguments as one string such as `"--build-arg https_proxy=$https_proxy"` (default "")
+* `--image-builder` string - tool to build OCI images. One of: `[docker, buildah]` (default "docker")
 * `-h, --help` - help for build
 
 ### Use