Add a preflight check that asserts docker connectivity

Assert that the docker daemon is running, and that we're able to connect to it.
This is done by executing 'docker ps', and checking the exit code.

This updates kubernetes-sigs#39
This fixes kubernetes-sigs#554

cmd/kind/create/cluster/createcluster.go

@@ -28,6 +28,7 @@ import (
 	"sigs.k8s.io/kind/pkg/cluster"
 	"sigs.k8s.io/kind/pkg/cluster/config/encoding"
 	"sigs.k8s.io/kind/pkg/cluster/create"
+	"sigs.k8s.io/kind/pkg/preflight/runtime"
 	"sigs.k8s.io/kind/pkg/util"
 )
 
@@ -77,6 +78,11 @@ func runE(flags *flagpole, cmd *cobra.Command, args []string) error {
 		return errors.New("aborting due to invalid configuration")
 	}
 
+	// Run container runtime preflight checks, connectivity etc.
+	if err := runtime.Preflight(); err != nil {
+		return err
+	}
+
 	// Check if the cluster name already exists
 	known, err := cluster.IsKnown(flags.Name)
 	if err != nil {

cmd/kind/delete/cluster/deletecluster.go

@@ -24,6 +24,7 @@ import (
 	"github.com/spf13/cobra"
 
 	"sigs.k8s.io/kind/pkg/cluster"
+	"sigs.k8s.io/kind/pkg/preflight/runtime"
 )
 
 type flagpole struct {
@@ -49,6 +50,11 @@ func NewCommand() *cobra.Command {
 }
 
 func runE(flags *flagpole, cmd *cobra.Command, args []string) error {
+	// Run container runtime preflight checks, connectivity etc.
+	if err := runtime.Preflight(); err != nil {
+		return err
+	}
+
 	// Check if the cluster name exists
 	known, err := cluster.IsKnown(flags.Name)
 	if err != nil {

cmd/kind/export/logs/logs.go

@@ -25,6 +25,7 @@ import (
 
 	"sigs.k8s.io/kind/pkg/cluster"
 	"sigs.k8s.io/kind/pkg/fs"
+	"sigs.k8s.io/kind/pkg/preflight/runtime"
 )
 
 type flagpole struct {
@@ -49,6 +50,11 @@ func NewCommand() *cobra.Command {
 }
 
 func runE(flags *flagpole, cmd *cobra.Command, args []string) error {
+	// Run container runtime preflight checks, connectivity etc.
+	if err := runtime.Preflight(); err != nil {
+		return err
+	}
+
 	// Check if the cluster name exists
 	known, err := cluster.IsKnown(flags.Name)
 	if err != nil {

cmd/kind/get/clusters/clusters.go

@@ -23,6 +23,7 @@ import (
 	"github.com/spf13/cobra"
 
 	"sigs.k8s.io/kind/pkg/cluster"
+	"sigs.k8s.io/kind/pkg/preflight/runtime"
 )
 
 // NewCommand returns a new cobra.Command for getting the list of clusters
@@ -41,6 +42,11 @@ func NewCommand() *cobra.Command {
 }
 
 func runE(cmd *cobra.Command, args []string) error {
+	// Run container runtime preflight checks, connectivity etc.
+	if err := runtime.Preflight(); err != nil {
+		return err
+	}
+
 	clusters, err := cluster.List()
 	if err != nil {
 		return err

cmd/kind/get/nodes/nodes.go

@@ -25,6 +25,7 @@ import (
 
 	"sigs.k8s.io/kind/pkg/cluster"
 	clusternodes "sigs.k8s.io/kind/pkg/cluster/nodes"
+	"sigs.k8s.io/kind/pkg/preflight/runtime"
 )
 
 type flagpole struct {
@@ -53,6 +54,11 @@ func NewCommand() *cobra.Command {
 }
 
 func runE(flags *flagpole, cmd *cobra.Command, args []string) error {
+	// Run container runtime preflight checks, connectivity etc.
+	if err := runtime.Preflight(); err != nil {
+		return err
+	}
+
 	// List nodes by cluster context name
 	n, err := clusternodes.ListByCluster()
 	if err != nil {

cmd/kind/load/docker-image/docker-image.go

@@ -28,6 +28,7 @@ import (
 	clusternodes "sigs.k8s.io/kind/pkg/cluster/nodes"
 	"sigs.k8s.io/kind/pkg/container/docker"
 	"sigs.k8s.io/kind/pkg/fs"
+	"sigs.k8s.io/kind/pkg/preflight/runtime"
 )
 
 type flagpole struct {
@@ -68,6 +69,11 @@ func NewCommand() *cobra.Command {
 }
 
 func runE(flags *flagpole, cmd *cobra.Command, args []string) error {
+	// Run container runtime preflight checks, connectivity etc.
+	if err := runtime.Preflight(); err != nil {
+		return err
+	}
+
 	// List nodes by cluster context name
 	n, err := clusternodes.ListByCluster()
 	if err != nil {

cmd/kind/load/image-archive/image-archive.go

@@ -25,6 +25,7 @@ import (
 
 	"sigs.k8s.io/kind/pkg/cluster"
 	clusternodes "sigs.k8s.io/kind/pkg/cluster/nodes"
+	"sigs.k8s.io/kind/pkg/preflight/runtime"
 )
 
 type flagpole struct {
@@ -65,6 +66,11 @@ func NewCommand() *cobra.Command {
 }
 
 func runE(flags *flagpole, cmd *cobra.Command, args []string) error {
+	// Run container runtime preflight checks, connectivity etc.
+	if err := runtime.Preflight(); err != nil {
+		return err
+	}
+
 	// List nodes by cluster context name
 	n, err := clusternodes.ListByCluster()
 	if err != nil {

pkg/preflight/runtime/docker.go

@@ -0,0 +1,31 @@
+package runtime
+
+import (
+	"github.com/pkg/errors"
+	"os/exec"
+)
+
+// Preflight runs checks to make sure that the container runtime
+// is working as expected
+func Preflight() error {
+	checks := []func() error{
+		dockerIsRunning,
+	}
+
+	for _, check := range checks {
+		if err := check(); err != nil {
+			return errors.Wrap(err, "Preflight check failed")
+		}
+	}
+
+	return nil
+}
+
+// dockerIsRunning asserts that the docker daemon is running and is responsive
+func dockerIsRunning() error {
+	err := exec.Command("docker", "ps").Run()
+	if err != nil {
+		return errors.Wrap(err, "Could not connect to a docker daemon")
+	}
+	return nil
+}