The ReturnString has to be present on the page you query with the test command TestCmd.
Take the start page of your application and set the TestCmd to get /index.jspor https://start_pageif you use wget to monitor the master server. Set the ReturnString to a string contained in the startpage. With this strategy, you are monitoring that the Apache Tomcat process of the N1 Grid Service Provisioning System Master Server is operational.
If the N1 Grid Service Provisioning System Master Server is configured for SSL on the administrative port. The only request on the http port is a page containing the string SSL. In this case configure the ReturnString to SSL and the TestCmd to get /index.jsp.
If you expect changes in the configurations, configure the test command to get /index.jsp and the RetunString to SSL|Service. This expression is true if the startpage contains SSL or Service.
If none of the above is appropriate, set the TestCmd to get /a-page-which-does-not-exists. In this case, set the ReturnString to a string contained in the Error Page. With this strategy, you are monitoring that the Apache Tomcat process of the N1 Grid Service Provisioning System Master Server is operational, because it registers that it must deliver a page that does not exist.
You can evaluate the different pages by connecting using a browser with hostname:port and specifying the different pages.