Improve environment handling

Dash in names are impractical for environment variables names.
Also, the required KUBE_ALERT_ prefix should be documented.

Author: bpineau

README.md

@@ -9,18 +9,18 @@ Currently support alerting to Datadog and logs (ie. syslog).
 Assuming you have go 1.9 and glide in the path, and GOPATH configured:
 
 ```shell
-make dep
+make deps
 make build
 ```
 
 ## Usage
 
-The daemon may run as a pod in the cluster, or outside of the cluster.
-He should find the Kubernetes api-server automatically, but you can
-provide this server's address with "-s" flag, or a full config with "-k".
+The daemon may run either as a pod, or outside of the Kubernetes cluster.
+He should find the Kubernetes api-server automatically (but you can
+provide this server's address with "-s" flag, or a kube config with "-k").
 
 You can pass configuration values either by command line arguments, or
-environment variables, or with a yaml configuration file.
+environment variables, a yaml configuration file, or a combination or those.
 
 The command line flags are:
 ```
@@ -33,7 +33,7 @@ Flags:
   -i, --datadog-api-key string   datadog api key
   -a, --datadog-app-key string   datadog app key
   -d, --dry-run                  dry-run mode
-  -p, --healthcheck-port int     port for answering healtchecks
+  -p, --healthcheck-port int     port for answering healthchecks
   -h, --help                     help for kube-alert
   -k, --kube-config string       kube config path
   -v, --log-level string         log level (default "debug")
@@ -56,3 +56,16 @@ datadog:
   app-key: xxx
 ```
 
+The environment variable consumed by kube-alert are option names prefixed
+by ```KUBE_ALERT_``` and using underscore instead of dash. Except KUBECONFIG,
+used without a prefix (to match kubernetes conventions).
+```
+env KUBECONFIG=/etc/kube/config \
+    KUBE_ALERT_HEALTHCHECK_PORT=8081 \
+    KUBE_ALERT_DATADOG.APP_KEY="xxx" \
+    KUBE_ALERT_DATADOG.API_KEY="xxx" \
+    KUBE_ALERT_DRY_RUN=true \
+    KUBE_ALERT_LOG.LEVEL=info \
+    KUBE_ALERT_API_SERVER="http://example.com:8080" \
+    kube-alert
+```

cmd/execute.go

@@ -2,6 +2,7 @@ package cmd
 
 import (
 	"os"
+	"strings"
 
 	"github.com/mitchellh/go-homedir"
 	"github.com/sirupsen/logrus"
@@ -85,7 +86,7 @@ func init() {
 	rootCmd.PersistentFlags().StringVarP(&ddApiKey, "datadog-api-key", "i", "", "datadog api key")
 	viper.BindPFlag("datadog.api-key", rootCmd.PersistentFlags().Lookup("datadog-api-key"))
 
-	rootCmd.PersistentFlags().IntVarP(&healthP, "healthcheck-port", "p", 0, "port for answering healtchecks")
+	rootCmd.PersistentFlags().IntVarP(&healthP, "healthcheck-port", "p", 0, "port for answering healthchecks")
 	viper.BindPFlag("healthcheck-port", rootCmd.PersistentFlags().Lookup("healthcheck-port"))
 }
 
@@ -107,6 +108,8 @@ func initConfig() {
 
 	// allow config params through prefixed env variables
 	viper.SetEnvPrefix("KUBE_ALERT")
+	replacer := strings.NewReplacer("-", "_")
+	viper.SetEnvKeyReplacer(replacer)
 	viper.AutomaticEnv()
 
 	if err := viper.ReadInConfig(); err == nil {