To connect to Amazon RDS MSSQL server we need a client software. In this case we use Sql Server Management Studio. Install it using the link SSMS .
After it is successfully installed we follow the steps below to connect it to the Amazon RDS.
Step-1
From the DB instance details get the end point.

Step-2
Use the end point and the master user credentials as the connection details.

Step-3
Once connected, we get the following window.

Step-4
We can also query the MSSQL DB as shown below.
