add support for config settings as environment variables

glide.lock

@@ -1,5 +1,5 @@
-hash: cb31830bb94bc7f841afb8023472f541aa1a4bf2297da8c05007c26900b8f7ce
-updated: 2016-09-13T12:37:36.929062201-07:00
+hash: b6857a2bb14d137d9d8a067bf9f3fa4519520ddfddc2105cd4dd99914d9ff1f9
+updated: 2016-09-13T14:08:54.366031279-07:00
 imports:
 - name: bitbucket.org/ww/goautoneg
   version: 75cd24fc2f2c2a2088577d12123ddee5f54e0675
@@ -38,6 +38,7 @@ imports:
   - pkg/cors
   - pkg/crc
   - pkg/fileutil
+  - pkg/flags
   - pkg/httputil
   - pkg/idutil
   - pkg/ioutil
@@ -119,7 +120,7 @@ imports:
 - name: github.com/prometheus/procfs
   version: 454a56f35412459b5e684fd5ec0f9211b94f002a
 - name: github.com/quantum/clusterd
-  version: a19ae6e0d43166b5e8cec10424cb2dcc9c13c7f3
+  version: 14dec27c9b5e2463555ac74674daf53c625fd619
   subpackages:
   - pkg/inventory
   - pkg/orchestrator

pkg/castled/cmd/castled.go

@@ -4,9 +4,11 @@ import (
 	"fmt"
 	"os"
 	"os/signal"
+	"strings"
 	"time"
 
 	"github.com/spf13/cobra"
+	"github.com/spf13/pflag"
 
 	"github.com/quantum/castle/pkg/castled"
 	"github.com/quantum/castle/pkg/util"
@@ -28,6 +30,10 @@ var rootCmd = &cobra.Command{
 	Long:  `https://github.com/quantum/castle`,
 }
 
+// Initialize the configuration parameters. The precedence from lowest to highest is:
+//  1) default value (at compilation)
+//  2) environment variables (upper case, replace - with _, and castle prefix. For example, discovery-url is CASTLE_DISCOVERY_URL)
+//  3) command line parameter
 func init() {
 	rootCmd.Flags().StringVar(&discoveryURL, "discovery-url", "", "etcd discovery URL. Example: http://discovery.castle.com/26bd83c92e7145e6b103f623263f61df")
 	rootCmd.Flags().StringVar(&etcdMembers, "etcd-members", "", "etcd members to connect to. Overrides the discovery URL. Example: http://10.23.45.56:2379")
@@ -36,6 +42,9 @@ func init() {
 	rootCmd.Flags().BoolVar(&forceFormat, "force-format", false,
 		"true to force the format of any specified devices, even if they already have a filesystem.  BE CAREFUL!")
 
+	// load the environment variables
+	setFlagsFromEnv(rootCmd.Flags())
+
 	rootCmd.MarkFlagRequired("private-ipv4")
 
 	rootCmd.RunE = joinCluster
@@ -52,6 +61,7 @@ func addCommands() {
 }
 
 func joinCluster(cmd *cobra.Command, args []string) error {
+
 	if err := util.VerifyRequiredFlags(cmd, []string{"private-ipv4"}); err != nil {
 		return err
 	}
@@ -80,3 +90,16 @@ func joinCluster(cmd *cobra.Command, args []string) error {
 
 	return nil
 }
+
+func setFlagsFromEnv(flags *pflag.FlagSet) error {
+	flags.VisitAll(func(f *pflag.Flag) {
+		envVar := "CASTLE_" + strings.Replace(strings.ToUpper(f.Name), "-", "_", -1)
+		value := os.Getenv(envVar)
+		if value != "" {
+			// Set the environment variable. Will override default values, but be overridden by command line parameters.
+			flags.Set(f.Name, value)
+		}
+	})
+
+	return nil
+}