kubeadm-init: allow overriding the dry-run temp directory

Allow overriding the dry-run temporary directory with
an env. variable (KUBEADM_INIT_DRYRUN_DIR).

Use the same variable in test/cmd/init_test.go.
This allows running integration tests as non-root.

Author: neolit123

cmd/kubeadm/app/cmd/init.go

@@ -357,7 +357,10 @@ func newInitData(cmd *cobra.Command, args []string, options *initOptions, out io
 	// if dry running creates a temporary folder for saving kubeadm generated files
 	dryRunDir := ""
 	if options.dryRun {
-		if dryRunDir, err = kubeadmconstants.CreateTempDirForKubeadm("", "kubeadm-init-dryrun"); err != nil {
+		// the KUBEADM_INIT_DRYRUN_DIR environment variable allows overriding the dry-run temporary
+		// directory from the command line. This makes it possible to run "kubeadm init" integration
+		// tests without root.
+		if dryRunDir, err = kubeadmconstants.CreateTempDirForKubeadm(os.Getenv("KUBEADM_INIT_DRYRUN_DIR"), "kubeadm-init-dryrun"); err != nil {
 			return nil, errors.Wrap(err, "couldn't create a temporary directory")
 		}
 	}

cmd/kubeadm/test/cmd/init_test.go

@@ -17,6 +17,8 @@ limitations under the License.
 package kubeadm
 
 import (
+	"fmt"
+	"os"
 	"os/exec"
 	"strings"
 	"testing"
@@ -30,6 +32,10 @@ import (
 )
 
 func runKubeadmInit(args ...string) (string, string, int, error) {
+	const dryRunDir = "KUBEADM_INIT_DRYRUN_DIR"
+	if err := os.Setenv(dryRunDir, os.TempDir()); err != nil {
+		panic(fmt.Sprintf("could not set the %s environment variable", dryRunDir))
+	}
 	kubeadmPath := getKubeadmPath()
 	kubeadmArgs := []string{"init", "--dry-run", "--ignore-preflight-errors=all"}
 	kubeadmArgs = append(kubeadmArgs, args...)