ignore default values for retry interval

add additional validation case

command/agent/retry_join.go

@@ -69,8 +69,15 @@ func (r *retryJoiner) Validate(config *Config) error {
 		if config.Server.RetryMaxAttempts != 0 {
 			return fmt.Errorf("server_join and retry_max cannot both be defined; try defining only server_join")
 		}
-		if config.Server.RetryInterval != "0" {
-			return fmt.Errorf("server_join and retry_interval cannot both be defined; prefer setting the server_join parameter")
+		if config.Server.RetryInterval != "0" && config.Server.RetryInterval != "" {
+			// 30s is the default value that is set, ignore if this is the case
+			if config.Server.RetryInterval != "30s" {
+				return fmt.Errorf("server_join and retry_interval cannot both be defined; prefer setting the server_join parameter")
+			}
+		}
+
+		if len(config.Server.ServerJoin.RetryJoin) != 0 && len(config.Server.ServerJoin.StartJoin) != 0 {
+			return fmt.Errorf("server_join and start_join cannot both be defined in the same stanza")
 		}
 	}
 

command/agent/retry_join_test.go

@@ -358,6 +358,21 @@ func TestRetryJoin_Validate(t *testing.T) {
 			isValid: true,
 			reason:  "server deprecated retry_join configuration should be valid",
 		},
+		{
+			config: &Config{
+				Server: &ServerConfig{
+					RetryInterval: "30s",
+					ServerJoin: &ServerJoin{
+						RetryJoin:        []string{"127.0.0.1"},
+						RetryMaxAttempts: 0,
+						RetryInterval:    time.Duration(20) * time.Second,
+						StartJoin:        []string{},
+					},
+				},
+			},
+			isValid: true,
+			reason:  "ignore default value for retry interval",
+		},
 	}
 
 	joiner := retryJoiner{}