public static FaultToleranceConfig getConfig(String appName) {
        if (appName == null) {
            return DEFAULT_CFG;
        } else {
            FaultToleranceConfig config = APP_CONFIGS.get(appName);
            return config == null ? DEFAULT_CFG : config;
        }
    }
Get config if absent, else return default

@param appName App name
@return FaultToleranceConfig of this app, or default config
fault/fault-tolerance/src/main/java/com/alipay/sofa/rpc/client/aft/FaultToleranceConfigManager.java