fix(server): serve artifacts directly from disk to support large arti…

…facts

When serving very large artifacts, first loading them into memory can potentially
cause the pod to go OOM/crash depending on how much memory is available and what
limits have been set.  Rather than loading it into memory, we can serve files
directly from disk.

Fixes #4588

Signed-off-by: Daniel Herman <dherman@factset.com>

server/artifacts/artifact_server.go

@@ -7,7 +7,9 @@ import (
 	"net/http"
 	"os"
 	"path"
+	"strconv"
 	"strings"
+	"time"
 
 	log "github.com/sirupsen/logrus"
 	"google.golang.org/grpc/codes"
@@ -62,15 +64,12 @@ func (a *ArtifactServer) GetArtifact(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	data, filename, err := a.getArtifact(ctx, wf, nodeId, artifactName)
+	err = a.returnArtifact(ctx, w, r, wf, nodeId, artifactName)
 
 	if err != nil {
 		a.serverInternalError(err, w)
 		return
 	}
-
-	w.Header().Add("Content-Disposition", fmt.Sprintf(`filename="%s"`, filename))
-	a.ok(w, data)
 }
 
 func (a *ArtifactServer) GetArtifactByUID(w http.ResponseWriter, r *http.Request) {
@@ -96,15 +95,12 @@ func (a *ArtifactServer) GetArtifactByUID(w http.ResponseWriter, r *http.Request
 		return
 	}
 
-	data, filename, err := a.getArtifact(ctx, wf, nodeId, artifactName)
+	err = a.returnArtifact(ctx, w, r, wf, nodeId, artifactName)
 
 	if err != nil {
 		a.serverInternalError(err, w)
 		return
 	}
-
-	w.Header().Add("Content-Disposition", fmt.Sprintf(`filename="%s"`, filename))
-	a.ok(w, data)
 }
 
 func (a *ArtifactServer) gateKeeping(r *http.Request) (context.Context, error) {
@@ -123,50 +119,58 @@ func (a *ArtifactServer) gateKeeping(r *http.Request) (context.Context, error) {
 	return a.gatekeeper.Context(ctx)
 }
 
-func (a *ArtifactServer) ok(w http.ResponseWriter, data []byte) {
-	w.WriteHeader(200)
-	_, err := w.Write(data)
-	if err != nil {
-		a.serverInternalError(err, w)
-	}
-}
-
 func (a *ArtifactServer) serverInternalError(err error, w http.ResponseWriter) {
 	w.WriteHeader(500)
 	_, _ = w.Write([]byte(err.Error()))
 }
 
-func (a *ArtifactServer) getArtifact(ctx context.Context, wf *wfv1.Workflow, nodeId, artifactName string) ([]byte, string, error) {
+func (a *ArtifactServer) returnArtifact(ctx context.Context, w http.ResponseWriter, r *http.Request, wf *wfv1.Workflow, nodeId, artifactName string) error {
 	kubeClient := auth.GetKubeClient(ctx)
 
 	art := wf.Status.Nodes[nodeId].Outputs.GetArtifactByName(artifactName)
 	if art == nil {
-		return nil, "", fmt.Errorf("artifact not found")
+		return fmt.Errorf("artifact not found")
 	}
 
 	driver, err := a.artDriverFactory(art, resources{kubeClient, wf.Namespace})
 	if err != nil {
-		return nil, "", err
+		return err
 	}
 	tmp, err := ioutil.TempFile("/tmp", "artifact")
 	if err != nil {
-		return nil, "", err
+		return err
 	}
 	tmpPath := tmp.Name()
 	defer func() { _ = os.Remove(tmpPath) }()
 
 	err = driver.Load(art, tmpPath)
 	if err != nil {
-		return nil, "", err
+		return err
+	}
+
+	file, err := os.Open(tmpPath)
+
+	if err != nil {
+		return err
 	}
 
-	file, err := ioutil.ReadFile(tmpPath)
+	defer file.Close()
+
+	stats, err := file.Stat()
+
 	if err != nil {
-		return nil, "", err
+		return err
 	}
-	log.WithFields(log.Fields{"size": len(file)}).Debug("Artifact file size")
 
-	return file, path.Base(art.GetKey()), nil
+	contentLength := strconv.FormatInt(stats.Size(), 10)
+	log.WithFields(log.Fields{"size": contentLength}).Debug("Artifact file size")
+
+	w.Header().Add("Content-Disposition", fmt.Sprintf(`filename="%s"`, path.Base(art.GetKey())))
+	w.WriteHeader(200)
+
+	http.ServeContent(w, r, "", time.Time{}, file)
+
+	return nil
 }
 
 func (a *ArtifactServer) getWorkflowAndValidate(ctx context.Context, namespace string, workflowName string) (*wfv1.Workflow, error) {