In SQL Server 2017 RC1, there were several feature enhancements of note:
SQL Server on Linux Active Directory integration – With RC1, SQL Server on Linux supports Active Directory Authentication, which enables domain-joined clients on either Windows or Linux to authenticate to SQL Server using their domain credentials and the Kerberos protocol. Check out the getting started instructions.
Transport Layer Security (TLS) to encrypt data – SQL Server on Linux can use TLS to encrypt data that is transmitted across a network between a client application and an instance of SQL Server. SQL Server on Linux supports the following TLS protocols: TLS 1.2, 1.1, and 1.0. Check out the getting started instructions.
Machine Learning Services enhancements – In RC1, we add more model management capabilities for R Services on Windows Server, including External Library Management. The new release also supports Native Scoring.
SQL Server Analysis Services (SSAS) – In addition to the enhancements to SSAS from previous CTPs of SQL Server 2017, RC1 adds additional Dynamic Management Views, enabling dependency analysis and reporting. See the Analysis Services blog for more information.
SQL Server Integration Services (SSIS) on Linux – The preview of SQL Server Integration Services on Linux now adds support for any Unicode ODBC driver, if it follows ODBC specifications. (ANSI ODBC driver is not supported.)
SQL Server Integration Services (SSIS) on Windows Server – RC1 adds support for SSIS scale out in highly available environments. Customers can now enable Always On for SSIS, setting up Windows Server failover clustering for the scale out master.
Linux AD support is big.