Simplify caching

This PR simplifies caching to the following rules, described in my
second design doc for artifact caching:

If remote cluster or push:true :
 1. Check if image exists remotely.
 2. If not, check if same digest exists locally. If it does, retag and repush.
 3. If not, rebuild and repush.

If local cluster, and push:false:
 1. Check if image exists locally
 2. If not, check if same digest exists locally. If it does, retag.
 3. If not, rebuild

Author: Priya Wadhwa

pkg/skaffold/build/cache/retrieve.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"sync"
 	"time"
 
 	"github.com/GoogleContainerTools/skaffold/pkg/skaffold/build"
@@ -42,185 +43,154 @@ type ImageDetails struct {
 	ID     string `yaml:"id,omitempty"`
 }
 
-type detailsErr struct {
-	details *cachedArtifactDetails
-	err     error
-}
-
 // RetrieveCachedArtifacts checks to see if artifacts are cached, and returns tags for cached images, otherwise a list of images to be built
 func (c *Cache) RetrieveCachedArtifacts(ctx context.Context, out io.Writer, artifacts []*latest.Artifact) ([]*latest.Artifact, []build.Artifact, error) {
 	if !c.useCache {
 		return artifacts, nil, nil
 	}
 
 	start := time.Now()
-	color.Default.Fprintln(out, "Checking cache...")
 
-	detailsErrs := make([]chan detailsErr, len(artifacts))
+	wg := sync.WaitGroup{}
+	builtImages := make([]bool, len(artifacts))
+	needToBuildImages := make([]bool, len(artifacts))
 
 	for i := range artifacts {
-		detailsErrs[i] = make(chan detailsErr, 1)
-
+		wg.Add(1)
 		i := i
 		go func() {
-			details, err := c.retrieveCachedArtifactDetails(ctx, artifacts[i])
-			detailsErrs[i] <- detailsErr{details: details, err: err}
+			defer wg.Done()
+			ok, err := c.retrieveCachedArtifact(ctx, out, artifacts[i])
+			if ok {
+				builtImages[i] = true
+				return
+			}
+			if err != nil {
+				logrus.Debugf("error finding cached artifact for %s: %v", artifacts[i].ImageName, err)
+			}
+			color.Default.Fprintf(out, " - %s: ", artifacts[i].ImageName)
+			color.Red.Fprintf(out, "Not Found. Rebuilding.\n")
+			needToBuildImages[i] = true
 		}()
 	}
 
+	wg.Wait()
+
 	var (
 		needToBuild []*latest.Artifact
 		built       []build.Artifact
 	)
 
-	for i, artifact := range artifacts {
-		color.Default.Fprintf(out, " - %s: ", artifact.ImageName)
-
-		select {
-		case <-ctx.Done():
-			return nil, nil, context.Canceled
-
-		case d := <-detailsErrs[i]:
-			details := d.details
-			err := d.err
-			if err != nil || details.needsRebuild {
-				color.Red.Fprintln(out, "Not found. Rebuilding.")
-				needToBuild = append(needToBuild, artifact)
-				continue
-			}
-
-			color.Green.Fprint(out, "Found")
-			if details.needsRetag {
-				color.Green.Fprint(out, ". Retagging")
-			}
-			if details.needsPush {
-				color.Green.Fprint(out, ". Pushing.")
-			}
-			color.Default.Fprintln(out)
-
-			if details.needsRetag {
-				if err := c.client.Tag(ctx, details.prebuiltImage, details.hashTag); err != nil {
-					return nil, nil, errors.Wrap(err, "retagging image")
-				}
-			}
-			if details.needsPush {
-				if _, err := c.client.Push(ctx, out, details.hashTag); err != nil {
-					return nil, nil, errors.Wrap(err, "pushing image")
-				}
-			}
-
+	for i, imageBuilt := range builtImages {
+		if imageBuilt {
 			built = append(built, build.Artifact{
-				ImageName: artifact.ImageName,
-				Tag:       details.hashTag,
+				ImageName: artifacts[i].ImageName,
+				Tag:       HashTag(artifacts[i]),
 			})
 		}
 	}
 
+	for i, imageBuilt := range needToBuildImages {
+		if imageBuilt {
+			needToBuild = append(needToBuild, artifacts[i])
+		}
+	}
+
 	color.Default.Fprintln(out, "Cache check complete in", time.Since(start))
 	return needToBuild, built, nil
 }
 
-type cachedArtifactDetails struct {
-	needsRebuild  bool
-	needsRetag    bool
-	needsPush     bool
-	prebuiltImage string
-	hashTag       string
-}
-
-func (c *Cache) retrieveCachedArtifactDetails(ctx context.Context, a *latest.Artifact) (*cachedArtifactDetails, error) {
+// retrieveCachedArtifact tries to retrieve a cached artifact.
+// If it cannot, it returns false.
+// If it can, it returns true.
+func (c *Cache) retrieveCachedArtifact(ctx context.Context, out io.Writer, a *latest.Artifact) (bool, error) {
 	hash, err := hashForArtifact(ctx, c.builder, a)
 	if err != nil {
-		return nil, errors.Wrapf(err, "getting hash for artifact %s", a.ImageName)
+		return false, errors.Wrapf(err, "getting hash for artifact %s", a.ImageName)
 	}
 	a.WorkspaceHash = hash
 	imageDetails, cacheHit := c.artifactCache[hash]
 	if !cacheHit {
-		return &cachedArtifactDetails{
-			needsRebuild: true,
-		}, nil
+		return false, nil
 	}
-	hashTag := HashTag(a)
-	il, err := c.imageLocation(ctx, imageDetails, hashTag)
-	if err != nil {
-		return nil, errors.Wrapf(err, "getting artifact details for %s", a.ImageName)
+	if c.localCluster && !c.pushImages {
+		return c.artifactExistsLocally(ctx, out, a, imageDetails)
 	}
-	return &cachedArtifactDetails{
-		needsRebuild:  needsRebuild(il, c.localCluster),
-		needsRetag:    needsRetag(il),
-		needsPush:     needsPush(il, c.localCluster, c.pushImages),
-		prebuiltImage: il.prebuiltImage,
-		hashTag:       hashTag,
-	}, nil
+	return c.artifactExistsRemotely(ctx, out, a, imageDetails)
 }
 
-// imageLocation holds information about where the image currently is
-type imageLocation struct {
-	existsRemotely bool
-	existsLocally  bool
-	prebuiltImage  string
-}
-
-func (c *Cache) imageLocation(ctx context.Context, imageDetails ImageDetails, tag string) (*imageLocation, error) {
-	// Check if tagged image exists remotely with the same digest
-	existsRemotely := imgExistsRemotely(tag, imageDetails.Digest, c.insecureRegistries)
-	existsLocally := false
-	if c.client != nil {
-		// See if this image exists in the local daemon
-		if c.client.ImageExists(ctx, tag) {
-			existsLocally = true
-		}
-	}
-	if existsLocally {
-		return &imageLocation{
-			existsLocally:  existsLocally,
-			existsRemotely: existsRemotely,
-			prebuiltImage:  tag,
-		}, nil
+// artifactExistsLocally assumes the artifact must exist locally.
+// This is called when using a local cluster and push:false.
+// 1. Check if image exists locally
+// 2. If not, check if same digest exists locally. If it does, retag.
+// 3. If not, rebuild
+// It returns true if the artifact exists locally, and false if not.
+func (c *Cache) artifactExistsLocally(ctx context.Context, out io.Writer, a *latest.Artifact, imageDetails ImageDetails) (bool, error) {
+	hashTag := HashTag(a)
+	if c.client.ImageExists(ctx, hashTag) {
+		color.Default.Fprintf(out, " - %s: ", a.ImageName)
+		color.Green.Fprintf(out, "Found\n")
+		return true, nil
 	}
 	// Check for a local image with the same digest as the image we want to build
 	prebuiltImage, err := c.retrievePrebuiltImage(imageDetails)
 	if err != nil {
-		return nil, errors.Wrapf(err, "getting prebuilt image")
-	}
-	return &imageLocation{
-		existsRemotely: existsRemotely,
-		existsLocally:  existsLocally,
-		prebuiltImage:  prebuiltImage,
-	}, nil
-}
-
-func needsRebuild(d *imageLocation, localCluster bool) bool {
-	// If using local cluster, rebuild if all of the following are true:
-	//   1. does not exist locally
-	//   2. can't retag a prebuilt image
-	if localCluster {
-		return !d.existsLocally && d.prebuiltImage == ""
+		return false, errors.Wrapf(err, "getting prebuilt image")
+	}
+	// If prebuilt image exists, tag it. Otherwise, return false, as artifact doesn't exist locally.
+	if prebuiltImage != "" {
+		color.Default.Fprintf(out, " - %s: ", a.ImageName)
+		color.Green.Fprintf(out, "Found. Retagging.\n")
+		if err := c.client.Tag(ctx, prebuiltImage, hashTag); err != nil {
+			return false, errors.Wrap(err, "retagging image")
+		}
+		return true, nil
 	}
-	// If using remote cluster, only rebuild image if all of the following are true:
-	//  1. does not exist locally
-	//  2. does not exist remotely
-	//  3. can't retag a prebuilt image
-	return !d.existsLocally && !d.existsRemotely && d.prebuiltImage == ""
+	return false, nil
 }
 
-func needsPush(d *imageLocation, localCluster, push bool) bool {
-	// If using local cluster...
-	if localCluster {
-		// ...  only push if specified and image does not exist remotely
-		return push && !d.existsRemotely
+// artifactExistsRemotely assumes the artifact must exist locally.
+// this is used when running a remote cluster, or when push:true
+// 1. Check if image exists remotely.
+// 2. If not, check if same digest exists locally. If it does, retag and repush.
+// 3. If not, rebuild.
+// It returns true if the artifact exists remotely, and false if not.
+func (c *Cache) artifactExistsRemotely(ctx context.Context, out io.Writer, a *latest.Artifact, imageDetails ImageDetails) (bool, error) {
+	hashTag := HashTag(a)
+	if imgExistsRemotely(hashTag, imageDetails.Digest, c.insecureRegistries) {
+		color.Default.Fprintf(out, " - %s: ", a.ImageName)
+		color.Green.Fprintf(out, "Found\n")
+		return true, nil
+	}
+
+	// Check if image exists locally.
+	if c.client.ImageExists(ctx, hashTag) {
+		color.Default.Fprintf(out, " - %s: ", a.ImageName)
+		color.Green.Fprintf(out, "Found Locally. Pushing.\n")
+		if _, err := c.client.Push(ctx, out, hashTag); err != nil {
+			return false, errors.Wrap(err, "retagging image")
+		}
+		return true, nil
 	}
-	// If using remote cluster, push if image does not exist remotely
-	return !d.existsRemotely
-}
 
-func needsRetag(d *imageLocation) bool {
-	// Don't need a retag if image already exists locally
-	if d.existsLocally {
-		return false
+	// Check for a local image with the same digest as the image we want to build
+	prebuiltImage, err := c.retrievePrebuiltImage(imageDetails)
+	if err != nil {
+		return false, errors.Wrapf(err, "getting prebuilt image")
+	}
+	// If prebuilt image exists, tag it and push it. Otherwise, return false, as artifact doesn't exist locally.
+	if prebuiltImage != "" {
+		color.Default.Fprintf(out, " - %s: ", a.ImageName)
+		color.Green.Fprintf(out, "Found Locally. Retagging and Pushing.\n")
+		if err := c.client.Tag(ctx, prebuiltImage, hashTag); err != nil {
+			return false, errors.Wrap(err, "retagging image")
+		}
+		if _, err := c.client.Push(ctx, out, hashTag); err != nil {
+			return false, errors.Wrap(err, "retagging image")
+		}
+		return true, nil
 	}
-	// If a prebuilt image is found locally, retag the image
-	return d.prebuiltImage != ""
+	return false, nil
 }
 
 func (c *Cache) retrievePrebuiltImage(details ImageDetails) (string, error) {