From 9c014e905651b941e14e4f909a5a51ce013768c3 Mon Sep 17 00:00:00 2001
From: "Derrick J. Wippler" <thrawn01@gmail.com>
Date: Wed, 22 Aug 2018 16:24:11 -0500
Subject: [PATCH] ETCD3_ENDPOINT can now accept comma separated etcd endpoints

---
 etcdutil/README.md | 129 ++++++++++++++++++++++++++++++++++-----------
 etcdutil/config.go |   3 +-
 2 files changed, 101 insertions(+), 31 deletions(-)

diff --git a/etcdutil/README.md b/etcdutil/README.md
index 6ede3c36..0ec3fc34 100644
--- a/etcdutil/README.md
+++ b/etcdutil/README.md
@@ -1,46 +1,115 @@
-## ETCD Leader Election
+## NewElection()
 Use etcd for leader election if you have several instances of a service running in production
 and you only want one of the service instances to preform a task.
 
 `LeaderElection` starts a goroutine which performs an election and maintains a leader
- while services join and leave the election. Calling `Stop()` will `Concede()` leadership if
-  we currently have it.
+while services join and leave the election. Calling `Stop()` will `Concede()` leadership if
+the service currently has it.
 
 ```go
 
 import (
     "github.com/mailgun/holster"
-    "github.com/mailgun/holster/election"
+    "github.com/mailgun/holster/etcdutil"
 )
 
-var wg holster.WaitGroup
-
-// Start the goroutine and preform the election
-leader, _ := election.NewElection("my-service", "", nil)
-
-// Handle graceful shutdown
-signalChan := make(chan os.Signal, 1)
-signal.Notify(signalChan, os.Interrupt, os.Kill)
-
-// Do periodic thing
-tick := time.NewTicker(time.Second * 2)
-wg.Loop(func() bool {
-    select {
-    case <-tick.C:
-        // Are we currently leader?
-        if leader.IsLeader() {
-            err := DoThing()
-            if err != nil {
-                // Have another instance DoThing(), we can't for some reason
-                leader.Concede()
+func main() {
+    var wg holster.WaitGroup
+
+    hostname, err := os.Hostname()
+    if err != nil {
+        fmt.Fprintf(os.Stderr, "while obtaining hostname: %s\n", err)
+        return
+    }
+
+    // Preform an election called 'my-service' with hostname as the candidate name
+    leader, _ := etcdutil.NewElection("my-service", hostname, nil)
+
+    // Handle graceful shutdown
+    signalChan := make(chan os.Signal, 1)
+    signal.Notify(signalChan, os.Interrupt, os.Kill)
+
+    // Do periodic thing
+    tick := time.NewTicker(time.Second * 2)
+    wg.Loop(func() bool {
+        select {
+        case <-tick.C:
+            // Are we currently leader?
+            if leader.IsLeader() {
+                err := DoThing()
+                if err != nil {
+                    // Have another instance DoThing(), we can't for some reason
+                    leader.Concede()
+                }
             }
+            return true
+        case <-signalChan:
+            leader.Stop()
+            return false
         }
-        return true
-    case <-signalChan:
-        leader.Stop()
-        return false
+    })
+    wg.Wait()
+}
+```
+
+## NewEtcdConfig()
+Designed to be used in applications that share the same etcd config
+and wish to reuse the same config throughout the application.
+
+```go
+import (
+    "os"
+    "fmt"
+
+    "github.com/mailgun/holster/etcdutil"
+)
+
+func main() {
+    // These environment variables provided by the environment,
+    // we set them here to only to illustrate how `NewEtcdConfig()`
+    // uses the environment to create a new etcd config
+    os.Setenv("ETCD3_USER", "root")
+    os.Setenv("ETCD3_PASSWORD", "rootpw")
+    os.Setenv("ETCD3_ENDPOINT", "etcd-n01:2379,etcd-n02:2379,etcd-n03:2379")
+
+    // These default to /etc/mailgun/ssl/localhost/etcd-xxx.pem if the files exist
+    os.Setenv("ETCD3_TLS_CERT", "/path/to/etcd-cert.pem")
+    os.Setenv("ETCD3_TLS_KEY", "/path/to/etcd-key.pem")
+    os.Setenv("ETCD3_CA", "/path/to/etcd-ca.pem")
+
+    // Create a new etc config from available environment variables
+    cfg, err := etcdutil.NewEtcdConfig(nil)
+    if err != nil {
+        fmt.Fprintf(os.Stderr, "while creating etcd config: %s\n", err)
+        return
     }
-})
-wg.Wait()
+
+    // Use cfg to init scroll
+    // Use cfg to init eventbus
+    // Use cfg to init leader election
+}
 ```
 
+## NewSecureClient()
+Just like `NewEtcdConfig()` but returns a connected etcd client for use by the
+rest of the application.
+
+```go
+import (
+    "os"
+    "fmt"
+
+    "github.com/mailgun/holster/etcdutil"
+)
+
+func main() {
+    // Create a new etc client from available environment variables
+    client, err := etcdutil.NewSecureClient(nil)
+    if err != nil {
+        fmt.Fprintf(os.Stderr, "while creating etcd client: %s\n", err)
+        return
+    }
+
+    // Use client
+}
+```
diff --git a/etcdutil/config.go b/etcdutil/config.go
index af15098c..17b12274 100644
--- a/etcdutil/config.go
+++ b/etcdutil/config.go
@@ -5,6 +5,7 @@ import (
 	"crypto/x509"
 	"io/ioutil"
 	"os"
+	"strings"
 	"time"
 
 	etcd "github.com/coreos/etcd/clientv3"
@@ -99,7 +100,7 @@ func NewEtcdConfig(cfg *etcd.Config) (*etcd.Config, error) {
 	}
 
 	holster.SetDefault(&envEndpoint, os.Getenv("ETCD3_ENDPOINT"), localEtcdEndpoint)
-	holster.SetDefault(&cfg.Endpoints, []string{envEndpoint})
+	holster.SetDefault(&cfg.Endpoints, strings.Split(envEndpoint, ","))
 
 	// Override here if user REALLY wants this
 	if cfg.TLS != nil && os.Getenv("ETCD3_SKIP_VERIFY") != "" {