Run kustomize and kubectl sequentially, without piping (#119)

This specifically fixes a bug where `ioutil.ReadAll` could block indefinitely
reading from kustomize's stderr pipe when kubectl exited before kustomize.

More generally, removing piping altogether reduces the complexity and
eliminates the distinct possibility of bugs like this being introduced again.

From my testing in exp-1-aws, where runs have been taking ~366 seconds, this
change adds about 4 seconds to the overall run latency. I think that's more than
acceptable.

kubectl/client.go

@@ -1,11 +1,9 @@
 package kubectl
 
 import (
+	"bytes"
 	"fmt"
-	"io"
-	"io/ioutil"
 	"os/exec"
-	"strings"
 
 	"github.com/utilitywarehouse/kube-applier/metrics"
 )
@@ -48,51 +46,30 @@ func (c *Client) Apply(path, namespace string, dryRun, kustomize bool, pruneWhit
 	}
 
 	kubectlCmd := exec.Command(args[0], args[1:]...)
+	cmdStr := kubectlCmd.String()
 
-	var cmdStr string
-	var kustomizeStderr io.ReadCloser
 	if kustomize {
-		cmdStr = "kustomize build " + path + " | " + strings.Join(args, " ")
+		var kustomizeStdout, kustomizeStderr bytes.Buffer
+
 		kustomizeCmd := exec.Command("kustomize", "build", path)
-		kustomizeStdout, err := kustomizeCmd.StdoutPipe()
-		if err != nil {
-			return cmdStr, "", err
-		}
-		kubectlCmd.Stdin = kustomizeStdout
-		kustomizeStderr, err = kustomizeCmd.StderrPipe()
-		if err != nil {
-			return cmdStr, "", err
-		}
+		kustomizeCmd.Stdout = &kustomizeStdout
+		kustomizeCmd.Stderr = &kustomizeStderr
 
-		err = kustomizeCmd.Start()
+		err := kustomizeCmd.Run()
 		if err != nil {
-			fmt.Printf("%s", err)
-			return cmdStr, "", err
+			return kustomizeCmd.String(), kustomizeStderr.String(), err
 		}
-		defer func() {
-			io.Copy(ioutil.Discard, kustomizeStdout)
-			io.Copy(ioutil.Discard, kustomizeStderr)
-			err = kustomizeCmd.Wait()
-			if err != nil {
-				fmt.Printf("%s", err)
-			}
-		}()
-	} else {
-		cmdStr = strings.Join(args, " ")
+
+		kubectlCmd.Stdin = &kustomizeStdout
+		cmdStr = kustomizeCmd.String() + " | " + cmdStr
 	}
 
 	out, err := kubectlCmd.CombinedOutput()
 	if err != nil {
 		if e, ok := err.(*exec.ExitError); ok {
 			c.Metrics.UpdateKubectlExitCodeCount(namespace, e.ExitCode())
 		}
-		var str strings.Builder
-		if kustomizeStderr != nil {
-			kustomizeErr, _ := ioutil.ReadAll(kustomizeStderr)
-			str.WriteString(string(kustomizeErr))
-		}
-		str.WriteString(string(out))
-		return cmdStr, str.String(), err
+		return cmdStr, string(out), err
 	}
 	c.Metrics.UpdateKubectlExitCodeCount(path, 0)