Add docker api version parameter (#372)

* Add docker api version parameter

* Note for minimum supported version

* Tests for EnvConfig

cmd/root.go

@@ -18,10 +18,6 @@ import (
 	"github.com/spf13/cobra"
 )
 
-// DockerAPIMinVersion is the minimum version of the docker api required to
-// use watchtower
-const DockerAPIMinVersion string = "1.24"
-
 var (
 	client         container.Client
 	scheduleSpec   string
@@ -90,7 +86,7 @@ func PreRun(cmd *cobra.Command, args []string) {
 	lifecycleHooks, _ = f.GetBool("enable-lifecycle-hooks")
 
 	// configure environment vars for client
-	err := flags.EnvConfig(cmd, DockerAPIMinVersion)
+	err := flags.EnvConfig(cmd)
 	if err != nil {
 		log.Fatal(err)
 	}

docs/arguments.md

@@ -75,7 +75,17 @@ Docker daemon socket to connect to. Can be pointed at a remote Docker host by sp
 Environment Variable: DOCKER_HOST
                 Type: String
              Default: "unix:///var/run/docker.sock"
-```      
+```
+
+## Docker API version
+The API version to use by the Docker client for connecting to the Docker daemon. The minimum supported version is 1.24.
+
+```
+            Argument: --api-version, -a
+Environment Variable: DOCKER_API_VERSION
+                Type: String
+             Default: "1.24"
+```
 
 ## Include stopped
 Will also include created and exited containers.

internal/flags/flags.go

@@ -9,11 +9,16 @@ import (
 	"github.com/spf13/viper"
 )
 
+// DockerAPIMinVersion is the minimum version of the docker api required to
+// use watchtower
+const DockerAPIMinVersion string = "1.24"
+
 // RegisterDockerFlags that are used directly by the docker api client
 func RegisterDockerFlags(rootCmd *cobra.Command) {
 	flags := rootCmd.PersistentFlags()
 	flags.StringP("host", "H", viper.GetString("DOCKER_HOST"), "daemon socket to connect to")
 	flags.BoolP("tlsverify", "v", viper.GetBool("DOCKER_TLS_VERIFY"), "use TLS and verify the remote")
+	flags.StringP("api-version", "a", viper.GetString("DOCKER_API_VERSION"), "api version to use by docker client")
 }
 
 // RegisterSystemFlags that are used by watchtower to modify the program flow
@@ -215,6 +220,7 @@ Should only be used for testing.
 func SetDefaults() {
 	viper.AutomaticEnv()
 	viper.SetDefault("DOCKER_HOST", "unix:///var/run/docker.sock")
+	viper.SetDefault("DOCKER_API_VERSION", DockerAPIMinVersion)
 	viper.SetDefault("WATCHTOWER_POLL_INTERVAL", 300)
 	viper.SetDefault("WATCHTOWER_TIMEOUT", time.Second*10)
 	viper.SetDefault("WATCHTOWER_NOTIFICATIONS", []string{})
@@ -225,10 +231,11 @@ func SetDefaults() {
 
 // EnvConfig translates the command-line options into environment variables
 // that will initialize the api client
-func EnvConfig(cmd *cobra.Command, dockerAPIMinVersion string) error {
+func EnvConfig(cmd *cobra.Command) error {
 	var err error
 	var host string
 	var tls bool
+	var version string
 
 	flags := cmd.PersistentFlags()
 
@@ -238,13 +245,16 @@ func EnvConfig(cmd *cobra.Command, dockerAPIMinVersion string) error {
 	if tls, err = flags.GetBool("tlsverify"); err != nil {
 		return err
 	}
+	if version, err = flags.GetString("api-version"); err != nil {
+		return err
+	}
 	if err = setEnvOptStr("DOCKER_HOST", host); err != nil {
 		return err
 	}
 	if err = setEnvOptBool("DOCKER_TLS_VERIFY", tls); err != nil {
 		return err
 	}
-	if err = setEnvOptStr("DOCKER_API_VERSION", dockerAPIMinVersion); err != nil {
+	if err = setEnvOptStr("DOCKER_API_VERSION", version); err != nil {
 		return err
 	}
 	return nil

internal/flags/flags_test.go

@@ -0,0 +1,39 @@
+package flags
+
+import (
+	"os"
+	"testing"
+
+	"github.com/spf13/cobra"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEnvConfig_Defaults(t *testing.T) {
+	cmd := new(cobra.Command)
+	SetDefaults()
+	RegisterDockerFlags(cmd)
+
+	err := EnvConfig(cmd)
+	require.NoError(t, err)
+
+	assert.Equal(t, "unix:///var/run/docker.sock", os.Getenv("DOCKER_HOST"))
+	assert.Equal(t, "", os.Getenv("DOCKER_TLS_VERIFY"))
+	assert.Equal(t, DockerAPIMinVersion, os.Getenv("DOCKER_API_VERSION"))
+}
+
+func TestEnvConfig_Custom(t *testing.T) {
+	cmd := new(cobra.Command)
+	SetDefaults()
+	RegisterDockerFlags(cmd)
+
+	err := cmd.ParseFlags([]string{"--host", "some-custom-docker-host", "--tlsverify", "--api-version", "1.99"})
+	require.NoError(t, err)
+
+	err = EnvConfig(cmd)
+	require.NoError(t, err)
+
+	assert.Equal(t, "some-custom-docker-host", os.Getenv("DOCKER_HOST"))
+	assert.Equal(t, "1", os.Getenv("DOCKER_TLS_VERIFY"))
+	assert.Equal(t, "1.99", os.Getenv("DOCKER_API_VERSION"))
+}