TODO.md

@@ -20,6 +20,9 @@ regress.
 
 # Completed Steps
 
+- 2026-09-23: After a successful deploy, upaas removes the app's images other
+  than the running one and the one rollback would use, together with the
+  untagged images they were built on (#216).
 - 2026-09-23: The git clone container is now removed together with its anonymous
   volume (the `alpine/git` image declares one at `/git`), so a deploy no longer
   leaves a Docker volume behind (#215).

internal/docker/client.go

@@ -537,6 +537,31 @@ func (c *Client) RemoveImage(ctx context.Context, imageID ImageID) error {
 	return nil
 }
 
+// ListImageIDs returns the IDs of all images tagged in the given repository,
+// such as "upaas-myapp".
+func (c *Client) ListImageIDs(
+	ctx context.Context,
+	repository string,
+) ([]ImageID, error) {
+	if c.docker == nil {
+		return nil, ErrNotConnected
+	}
+
+	images, err := c.docker.ImageList(ctx, image.ListOptions{
+		Filters: filters.NewArgs(filters.Arg("reference", repository)),
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to list images: %w", err)
+	}
+
+	ids := make([]ImageID, 0, len(images))
+	for _, img := range images {
+		ids = append(ids, ImageID(img.ID))
+	}
+
+	return ids, nil
+}
+
 func (c *Client) performBuild(
 	ctx context.Context,
 	opts BuildImageOptions,

internal/service/deploy/deploy.go

@@ -534,6 +534,8 @@ func (svc *Service) runBuildAndDeploy(
 		return err
 	}
 
+	svc.removeUnusedImages(bgCtx, app, deployment)
+
 	// Use context.WithoutCancel to ensure health check completes even if
 	// the parent context is cancelled (e.g., HTTP request ends).
 	go svc.checkHealthAfterDelay(bgCtx, app, deployment)
@@ -714,6 +716,57 @@ func (svc *Service) checkCancelled(
 	return ErrDeployCancelled
 }
 
+// removeUnusedImages removes the app's images (tagged upaas-<app>:<deployment>
+// by buildImage) except the one the running container uses and the one
+// Rollback would start. Removing an image also removes the untagged images
+// it was built on, unless another image still needs them.
+func (svc *Service) removeUnusedImages(
+	ctx context.Context,
+	app *models.App,
+	deployment *models.Deployment,
+) {
+	images, err := svc.docker.ListImageIDs(ctx, "upaas-"+app.Name)
+	if err != nil {
+		svc.log.Error("failed to list app images", "error", err, "app", app.Name)
+
+		return
+	}
+
+	for _, imageID := range unusedImages(images, app) {
+		removeErr := svc.docker.RemoveImage(ctx, imageID)
+		if removeErr != nil {
+			svc.log.Error("failed to remove old image",
+				"error", removeErr, "app", app.Name, "image", imageID)
+			_ = deployment.AppendLog(
+				ctx,
+				"WARNING: failed to remove old image "+
+					imageID.String()+": "+removeErr.Error(),
+			)
+
+			continue
+		}
+
+		_ = deployment.AppendLog(ctx, "Removed old image: "+imageID.String())
+	}
+}
+
+// unusedImages returns the images that are neither the app's current image
+// nor its previous image, which Rollback uses.
+func unusedImages(images []docker.ImageID, app *models.App) []docker.ImageID {
+	var unused []docker.ImageID
+
+	for _, imageID := range images {
+		if imageID.String() == app.ImageID.String ||
+			imageID.String() == app.PreviousImageID.String {
+			continue
+		}
+
+		unused = append(unused, imageID)
+	}
+
+	return unused
+}
+
 // cleanupCancelledDeploy removes orphan resources left by a cancelled deployment.
 func (svc *Service) cleanupCancelledDeploy(
 	ctx context.Context,

internal/service/deploy/deploy_images_test.go

@@ -0,0 +1,48 @@
+package deploy_test
+
+import (
+	"database/sql"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"sneak.berlin/go/upaas/internal/docker"
+	"sneak.berlin/go/upaas/internal/models"
+	"sneak.berlin/go/upaas/internal/service/deploy"
+)
+
+const currentImage = "sha256:current"
+
+func TestUnusedImages_KeepsCurrentAndRollbackImage(t *testing.T) {
+	t.Parallel()
+
+	app := &models.App{
+		ImageID:         sql.NullString{String: currentImage, Valid: true},
+		PreviousImageID: sql.NullString{String: "sha256:previous", Valid: true},
+	}
+	images := []docker.ImageID{
+		"sha256:oldest",
+		"sha256:previous",
+		"sha256:older",
+		currentImage,
+	}
+
+	assert.Equal(t,
+		[]docker.ImageID{"sha256:oldest", "sha256:older"},
+		deploy.UnusedImages(images, app),
+	)
+}
+
+func TestUnusedImages_FirstDeployHasNoRollbackImage(t *testing.T) {
+	t.Parallel()
+
+	app := &models.App{
+		ImageID: sql.NullString{String: currentImage, Valid: true},
+	}
+	images := []docker.ImageID{currentImage, "sha256:failed"}
+
+	assert.Equal(t,
+		[]docker.ImageID{"sha256:failed"},
+		deploy.UnusedImages(images, app),
+	)
+}

internal/service/deploy/export_test.go

@@ -90,6 +90,11 @@ func (svc *Service) GetBuildDirExported(appName string) string {
 	return svc.GetBuildDir(appName)
 }
 
+// UnusedImages exposes unusedImages for testing.
+func UnusedImages(images []docker.ImageID, app *models.App) []docker.ImageID {
+	return unusedImages(images, app)
+}
+
 // BuildContainerOptionsExported exposes buildContainerOptions for testing.
 func (svc *Service) BuildContainerOptionsExported(
 	ctx context.Context,