If the HTTP policy to enable HTTPS is specified, the RM and AM are initialized with SSL listeners. The RM has a web app proxy servlet that acts as a proxy for incoming AM requests. In order to forward the requests to the AM the proxy servlet makes use of HttpClient. However, the HttpClient utilized is not initialized correctly with the necessary certs to allow for successful one way SSL invocations to the other nodes in the cluster (it is not configured to access/load the client truststore specified in ssl-client.xml). I imagine SSLFactory.createSSLSocketFactory() could be utilized to create an instance that can be assigned to the HttpClient.
The symptoms of this issue are:
AM: Displays "unknown_certificate" exception
RM: Displays an exception such as "javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target"