This is how we enable Tomcat Manager in a vanilla Tomcat 8.
I have a hardened Tomcat 8 that is split into CATALINA_HOME AND CATALINA_BASE which I was unable to deploy Tomcat Manager on, without having the following error:
org.apache.catalina.core.ContainerBase addChildInternal SEVERE: ContainerBase.addChild: start: org.apache.catalina.LifecycleException: Failed to start component [/manager]
and
SEVERE: The web application with context path [/manager] was not deployed because it contained a deployment descriptor [\webapps\manager\META-INF\context.xml] which may include configuration necessary for the secure deployment of the application but processing of deployment descriptors is prevented by the deployXML setting of this host. An appropriate descriptor should be created at [\conf\Catalina\localhost\manager.xml] to deploy this application.
Similar posts (to list a few 1, 2, 3, 4) suggested solutions but did not help.