helper/communicator: configurable handshake attempts [GH-1988]

helper/communicator/config.go

@@ -20,6 +20,7 @@ type Config struct {
 	SSHPrivateKey        string        `mapstructure:"ssh_private_key_file"`
 	SSHPty               bool          `mapstructure:"ssh_pty"`
 	SSHTimeout           time.Duration `mapstructure:"ssh_timeout"`
+	SSHHandshakeAttempts int           `mapstructure:"ssh_handshake_attempts"`
 }
 
 func (c *Config) Prepare(ctx *interpolate.Context) []error {
@@ -35,6 +36,10 @@ func (c *Config) Prepare(ctx *interpolate.Context) []error {
 		c.SSHTimeout = 5 * time.Minute
 	}
 
+	if c.SSHHandshakeAttempts == 0 {
+		c.SSHHandshakeAttempts = 10
+	}
+
 	// Validation
 	var errs []error
 	if c.Type == "ssh" {

helper/communicator/step_connect_ssh.go

@@ -149,8 +149,10 @@ func (s *StepConnectSSH) waitForSSH(state multistep.StateBag, cancel <-chan stru
 				handshakeAttempts += 1
 			}
 
-			if handshakeAttempts < 10 {
+			if handshakeAttempts < s.Config.SSHHandshakeAttempts {
-				// Try to connect via SSH a handful of times
+				// Try to connect via SSH a handful of times. We sleep here
+				// so we don't get a ton of authentication errors back to back.
+				time.Sleep(2 * time.Second)
 				continue
 			}