Bump Docker supported version to 18.09

cmd/kubeadm/app/util/system/docker_validator.go

@@ -38,7 +38,7 @@ func (d *DockerValidator) Name() string {
 
 const (
 	dockerConfigPrefix           = "DOCKER_"
-	latestValidatedDockerVersion = "18.06"
+	latestValidatedDockerVersion = "18.09"
 )
 
 // TODO(random-liu): Add more validating items.

cmd/kubeadm/app/util/system/docker_validator_test.go

@@ -92,8 +92,14 @@ func TestValidateDockerInfo(t *testing.T) {
 			warn: false,
 		},
 		{
-			name: "Docker version 18.09.0 is not in the list of validated versions",
-			info: types.Info{Driver: "driver_2", ServerVersion: "18.09.0"},
+			name: "valid Docker version 18.09.1-ce",
+			info: types.Info{Driver: "driver_2", ServerVersion: "18.09.1-ce"},
+			err:  false,
+			warn: false,
+		},
+		{
+			name: "Docker version 19.01.0 is not in the list of validated versions",
+			info: types.Info{Driver: "driver_2", ServerVersion: "19.01.0"},
 			err:  false,
 			warn: true,
 		},

test/images/image-util.sh

@@ -103,6 +103,8 @@ build() {
 }
 
 docker_version_check() {
+  # The reason for this version check is even though "docker manifest" command is available in 18.03, it does
+  # not work properly in that version. So we insist on 18.06.0 or higher.
   docker_version=$(docker version --format '{{.Client.Version}}' | cut -d"-" -f1)
   if [[ ${docker_version} != 18.06.0 && ${docker_version} < 18.06.0 ]]; then
     echo "Minimum docker version 18.06.0 is required for creating and pushing manifest images[found: ${docker_version}]"