After a clean installation of:
bitnami-drupal-7.41-0-linux-ubuntu-14.04.1-x86_64-hvm-ebs - ami-5d1d222a
It is not possible to install any multisite on the system using the Drupal Installation procedure (install.php)
(create a site folder under /sites/domain_name ,and add settings.php)
So when setting up a new multisite, the drupal installation asks the database username, password and also "socket". Whatever you put in the fields, the response is:
Failed to connect to your database server. The server reports the following message: SQLSTATE[HY000]  No such file or directory.
Failed to connect to your database server. The server reports the following message: SQLSTATE[HY000]  No handler for this scheme.
This happens when the host is the Amazon RDS instance name. I have been installing about 100 multi sites using previous Drupal Bitnami stacks, and never faced this problem before.
(I think the problem is related to Bitnami stack does not have mysql.sock -file or some php 5.5 etc misconfiguration)
So how I managed to install a new multisite which uses RDS is just to edit manually the settings.php.
So when the Drupal installation procedure is on the step 2 (when asking database name, password etc.) edit manually the settings.php and add RDS host name, database name and passwrod. After that refresh the page and the installation continues.
So my question is, why drupal 7.41 installation asks "socket" -name? Usually with older Bitnami stacks (7.39) it did not ask any sockets. And what is the socket name for Amazon RDS instance if Drupal needs it?