It has been observed that Tomcat Manager is not accessible after starting the Tomcat Server from Eclipse. Even after doing changes in file – $TOMCAT_HOME/conf/tomcat-users.xml changes are not getting reflected back.
Therefore, we need to configure Eclipse to take control over from Tomcat, we need to do double-click the Tomcat Server entry in Servers tab and then we will get the server configuration. At the left column, under Server Locations, select Use Tomcat installations (If it is grayed-out then delete the Server and add it again). This way Eclipse will take full control over Tomcat and we will be able to access the default Tomcat homepage with the Tomcat Manager when running from inside Eclipse.
Note: Above stated configuration is validated on Apache-Tomcat-8.0.33