only init one consul client, and lower keepalive

The consul Client is analogous to an http.Client, and we really don't
need more than 1. Configure a single client and store it in the backend.

Replace the default Transport's Dialer to reduce the KeepAlive setting
from 30s to 17s. This avoids racing with the common network timeout
value of 30s, and is also coprime to other common intervals.

backend/remote-state/consul/backend.go

@@ -2,7 +2,9 @@ package consul
 
 import (
 	"context"
+	"net"
 	"strings"
+	"time"
 
 	consulapi "github.com/hashicorp/consul/api"
 	"github.com/hashicorp/terraform/backend"
@@ -100,6 +102,7 @@ type Backend struct {
 	*schema.Backend
 
 	// The fields below are set from configure
+	client     *consulapi.Client
 	configData *schema.ResourceData
 	lock       bool
 }
@@ -111,16 +114,18 @@ func (b *Backend) configure(ctx context.Context) error {
 	// Store the lock information
 	b.lock = b.configData.Get("lock").(bool)
 
-	// Initialize a client to test config
-	_, err := b.clientRaw()
-	return err
-}
-
-func (b *Backend) clientRaw() (*consulapi.Client, error) {
 	data := b.configData
 
 	// Configure the client
 	config := consulapi.DefaultConfig()
+
+	// replace the default Transport Dialer to reduce the KeepAlive
+
+	config.Transport.DialContext = (&net.Dialer{
+		Timeout:   30 * time.Second,
+		KeepAlive: 17 * time.Second,
+	}).DialContext
+
 	if v, ok := data.GetOk("access_token"); ok && v.(string) != "" {
 		config.Token = v.(string)
 	}
@@ -162,5 +167,11 @@ func (b *Backend) clientRaw() (*consulapi.Client, error) {
 		}
 	}
 
-	return consulapi.NewClient(config)
+	client, err := consulapi.NewClient(config)
+	if err != nil {
+		return err
+	}
+
+	b.client = client
+	return nil
 }

backend/remote-state/consul/backend_state.go

@@ -15,15 +15,9 @@ const (
 )
 
 func (b *Backend) States() ([]string, error) {
-	// Get the Consul client
-	client, err := b.clientRaw()
-	if err != nil {
-		return nil, err
-	}
-
 	// List our raw path
 	prefix := b.configData.Get("path").(string) + keyEnvPrefix
-	keys, _, err := client.KV().Keys(prefix, "/", nil)
+	keys, _, err := b.client.KV().Keys(prefix, "/", nil)
 	if err != nil {
 		return nil, err
 	}
@@ -60,28 +54,16 @@ func (b *Backend) DeleteState(name string) error {
 		return fmt.Errorf("can't delete default state")
 	}
 
-	// Get the Consul API client
-	client, err := b.clientRaw()
-	if err != nil {
-		return err
-	}
-
 	// Determine the path of the data
 	path := b.path(name)
 
 	// Delete it. We just delete it without any locking since
 	// the DeleteState API is documented as such.
-	_, err = client.KV().Delete(path, nil)
+	_, err := b.client.KV().Delete(path, nil)
 	return err
 }
 
 func (b *Backend) State(name string) (state.State, error) {
-	// Get the Consul API client
-	client, err := b.clientRaw()
-	if err != nil {
-		return nil, err
-	}
-
 	// Determine the path of the data
 	path := b.path(name)
 
@@ -91,7 +73,7 @@ func (b *Backend) State(name string) (state.State, error) {
 	// Build the state client
 	var stateMgr state.State = &remote.State{
 		Client: &RemoteClient{
-			Client:    client,
+			Client:    b.client,
 			Path:      path,
 			GZip:      gzip,
 			lockState: b.lock,