Support docker machine for kubeconfig.yaml

The kubeconfig.yaml generated by K3S uses local host as the host name by
default. It won't work when running with docker machine.

This patch detects if the docker environment is set up with docker
machine. If it is, then replace the host name to the IP address of
the docker machine.

cli/cluster.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"path"
 	"strconv"
+	"strings"
 
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/api/types/filters"
@@ -139,8 +140,23 @@ func createKubeConfigFile(cluster string) error {
 	}
 	defer kubeconfigfile.Close()
 
-	// write to file, skipping the first 512 bytes which contain file metadata and trimming any NULL characters
-	_, err = kubeconfigfile.Write(bytes.Trim(readBytes[512:], "\x00"))
+	// write to file, skipping the first 512 bytes which contain file metadata
+	// and trimming any NULL characters
+	trimBytes := bytes.Trim(readBytes[512:], "\x00")
+
+	// If running on a docker machine, replace localhost with
+	// docker machine's IP
+	dockerMachineIp, err := getDockerMachineIp()
+	if err != nil {
+		return err
+	}
+
+	if dockerMachineIp != "" {
+		s := string(trimBytes)
+		s = strings.Replace(s, "localhost", dockerMachineIp, 1)
+		trimBytes = []byte(s)
+	}
+	_, err = kubeconfigfile.Write(trimBytes)
 	if err != nil {
 		return fmt.Errorf("ERROR: couldn't write to kubeconfig.yaml\n%+v", err)
 	}

cli/docker-machine.go

@@ -0,0 +1,26 @@
+package run
+
+import (
+	"os"
+	"os/exec"
+	"strings"
+)
+
+func getDockerMachineIp() (string, error) {
+	machine := os.ExpandEnv("$DOCKER_MACHINE_NAME")
+
+	if machine == "" {
+		return "", nil
+	}
+
+	dockerMachinePath, err := exec.LookPath("docker-machine")
+	if err != nil {
+		return "", err
+	}
+
+	out, err := exec.Command(dockerMachinePath, "ip").Output()
+
+	ipStr := strings.TrimSuffix(string(out), "\n")
+	ipStr = strings.TrimSuffix(ipStr, "\r")
+	return ipStr, err
+}