Add option to render manifest from previous build result

cmd/skaffold/app/cmd/render.go

@@ -1,5 +1,5 @@
 /*
-Copyright 2019 The Skaffold Authors
+Copyright 2020 The Skaffold Authors
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -20,18 +20,22 @@ import (
 	"context"
 	"io"
 	"io/ioutil"
+	"os"
 
 	"github.com/pkg/errors"
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
 
+	"github.com/GoogleContainerTools/skaffold/cmd/skaffold/app/flags"
+	"github.com/GoogleContainerTools/skaffold/pkg/skaffold/build"
 	"github.com/GoogleContainerTools/skaffold/pkg/skaffold/runner"
 	"github.com/GoogleContainerTools/skaffold/pkg/skaffold/schema/latest"
 )
 
 var (
-	showBuild        bool
-	renderOutputPath string
+	fromBuildFileOutputPath string
+	showBuild               bool
+	renderOutputPath        string
 )
 
 // NewCmdRender describes the CLI command to build artifacts render Kubernetes manifests.
@@ -40,6 +44,7 @@ func NewCmdRender() *cobra.Command {
 		WithDescription("[alpha] Perform all image builds, and output rendered Kubernetes manifests").
 		WithCommonFlags().
 		WithFlags(func(f *pflag.FlagSet) {
+			f.StringVar(&fromBuildFileOutputPath, "from-build-file-output", "", "Don't build, but use file created with `skaffold build --file-output`")
 			f.BoolVar(&showBuild, "loud", false, "Show the build logs and output")
 			f.StringVar(&renderOutputPath, "output", "", "file to write rendered manifests to")
 		}).
@@ -53,10 +58,29 @@ func doRender(ctx context.Context, out io.Writer) error {
 	}
 
 	return withRunner(ctx, func(r runner.Runner, config *latest.SkaffoldConfig) error {
-		bRes, err := r.BuildAndTest(ctx, buildOut, targetArtifacts(opts, config))
+		var bRes []build.Artifact
 
-		if err != nil {
-			return errors.Wrap(err, "executing build")
+		if fromBuildFileOutputPath != "" {
+			if _, err := os.Stat(fromBuildFileOutputPath); os.IsNotExist(err) {
+				return errors.Wrap(err, "reading build file output")
+			}
+			buf, err := ioutil.ReadFile(fromBuildFileOutputPath)
+			if err != nil {
+				return errors.Wrap(err, "reading build file output")
+			}
+
+			buildOutput, err := flags.ParseBuildOutput(buf)
+			if err != nil {
+				return errors.Wrap(err, "parsing build file output")
+			}
+
+			bRes = buildOutput.Builds
+		} else {
+			var err error
+			bRes, err = r.BuildAndTest(ctx, buildOut, targetArtifacts(opts, config))
+			if err != nil {
+				return errors.Wrap(err, "executing build")
+			}
 		}
 
 		if err := r.Render(ctx, out, bRes, renderOutputPath); err != nil {

docs/content/en/docs/references/cli/_index.md

@@ -652,6 +652,7 @@ The following options can be passed to any command:
 Options:
   -d, --default-repo='': Default repository value (overrides global config)
   -f, --filename='skaffold.yaml': Filename or URL to the pipeline file
+      --from-build-file-output='': Don't build, but use file created with `skaffold build --file-output`
       --loud=false: Show the build logs and output
   -n, --namespace='': Run deployments in the specified namespace
       --output='': file to write rendered manifests to