Fallback to env backend

backends/client.go

@@ -13,6 +13,7 @@ import (
 	"github.com/kelseyhightower/confd/backends/stackengine"
 	"github.com/kelseyhightower/confd/backends/vault"
 	"github.com/kelseyhightower/confd/backends/zookeeper"
+	"github.com/kelseyhightower/confd/backends/fallback"
 	"github.com/kelseyhightower/confd/log"
 )
 
@@ -30,6 +31,22 @@ func New(config Config) (StoreClient, error) {
 	}
 	backendNodes := config.BackendNodes
 	log.Info("Backend nodes set to " + strings.Join(backendNodes, ", "))
+        if config.BackendFallback != "" {
+                mainConfig := config
+		fallbackConfig := config
+		mainConfig.BackendFallback = ""
+		fallbackConfig.Backend = config.BackendFallback
+		fallbackConfig.BackendFallback = ""
+		backendMain, err :=  New(mainConfig)
+		if err != nil {
+			return nil, err
+		}
+		backendFallback, err := New(fallbackConfig)
+                if err != nil {
+			return nil, err
+		}
+		return fallback.NewFallbackClient(backendMain, backendFallback)
+	}
 	switch config.Backend {
 	case "consul":
 		return consul.New(config.BackendNodes, config.Scheme,

backends/config.go

@@ -4,6 +4,7 @@ type Config struct {
 	AuthToken    string
 	AuthType     string
 	Backend      string
+        BackendFallback string
 	BasicAuth    bool
 	ClientCaKeys string
 	ClientCert   string

backends/fallback/client.go

@@ -0,0 +1,49 @@
+package fallback
+
+import (
+        "fmt"
+
+        "github.com/kelseyhightower/confd/log"
+)
+
+
+type StoreClient interface {
+        GetValues(keys []string) (map[string]string, error)
+        WatchPrefix(prefix string, keys []string, waitIndex uint64, stopChan chan bool) (uint64, error)
+}
+
+// Client provides a shell for the env client
+type FallbackClient struct{
+	mainBackend StoreClient
+	fallbackBackend StoreClient
+}
+
+// NewEnvClient returns a new client
+func NewFallbackClient(mainBackend StoreClient, fallbackBackend StoreClient) (*FallbackClient, error) {
+        return &FallbackClient{mainBackend, fallbackBackend}, nil
+}
+
+// GetValues queries the environment for keys
+func (c *FallbackClient) GetValues(keys []string) (map[string]string, error) {
+        fallback_vars, err := c.fallbackBackend.GetValues(keys)
+        if err != nil {
+                return nil, err
+        }
+
+	vars, err := c.mainBackend.GetValues(keys)
+	if err == nil {
+		log.Info(fmt.Sprintf("Key Map: %#v", vars))
+		for k, v := range vars {
+			fallback_vars[k] = v
+		}
+	}
+
+        log.Info(fmt.Sprintf("Key Map: %#v", fallback_vars))
+        return fallback_vars, nil
+}
+
+
+func (c *FallbackClient) WatchPrefix(prefix string, keys []string, waitIndex uint64, stopChan chan bool) (uint64, error) {
+        return c.mainBackend.WatchPrefix(prefix, keys, waitIndex, stopChan)
+}
+

config.go

@@ -23,6 +23,7 @@ var (
 	authToken         string
 	authType          string
 	backend           string
+        backendFallback   string
 	basicAuth         bool
 	clientCaKeys      string
 	clientCert        string
@@ -56,6 +57,7 @@ type Config struct {
 	AuthToken    string   `toml:"auth_token"`
 	AuthType     string   `toml:"auth_type"`
 	Backend      string   `toml:"backend"`
+	BackendFallback  string   `toml:"backend_fallback"`
 	BasicAuth    bool     `toml:"basic_auth"`
 	BackendNodes []string `toml:"nodes"`
 	ClientCaKeys string   `toml:"client_cakeys"`
@@ -81,6 +83,7 @@ type Config struct {
 func init() {
 	flag.StringVar(&authToken, "auth-token", "", "Auth bearer token to use")
 	flag.StringVar(&backend, "backend", "etcd", "backend to use")
+	flag.StringVar(&backendFallback, "backend-fallback", "", "backend to fallback to on none existing keys")
 	flag.BoolVar(&basicAuth, "basic-auth", false, "Use Basic Auth to authenticate (only used with -backend=etcd)")
 	flag.StringVar(&clientCaKeys, "client-ca-keys", "", "client ca keys")
 	flag.StringVar(&clientCert, "client-cert", "", "the client cert")
@@ -208,6 +211,7 @@ func initConfig() error {
 		AuthToken:    config.AuthToken,
 		AuthType:     config.AuthType,
 		Backend:      config.Backend,
+                BackendFallback: config.BackendFallback,
 		BasicAuth:    config.BasicAuth,
 		ClientCaKeys: config.ClientCaKeys,
 		ClientCert:   config.ClientCert,
@@ -280,6 +284,8 @@ func setConfigFromFlag(f *flag.Flag) {
 		config.AuthType = authType
 	case "backend":
 		config.Backend = backend
+        case "backend-fallback":
+                config.BackendFallback = backendFallback
 	case "basic-auth":
 		config.BasicAuth = basicAuth
 	case "client-cert":

docs/quick-start-guide.md

@@ -203,6 +203,14 @@ database_url = db.example.com
 database_user = rob
 ```
 
+## Fallback to env
+
+Fallback to env on key that aren't defined in etcd/consul or others backends:
+
+```
+confd -onetime -backend consul -backend-fallback env -node 127.0.0.0:8500
+```
+
 ## Advanced Example
 
 In this example we will use confd to manage two nginx config files using a single template.