========================== Creating target directory... ========================== Command start time 2016-03-22 05:55:43 Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password). SSH command execution finished host=192.168.91.128, exitcode=255 Command end time 2016-03-22 05:55:44 ERROR: Bootstrap of host 192.168.91.128 fails because previous action finished with non-zero exit code (255) ERROR MESSAGE: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password). STDOUT: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).
Check if you have provided the correct ssh key. The key should be the private ssh key and not the public ssh key. On the command line try to ssh manually with those credentials and see if you can SSH.
Try ssh to 192.168.91.128 and confirm that password is not required.
If you really have setup password less SSH correctly and are using the private key please try and upgrade your OpenSSL version. The version of openssl should be above 1.0.1e-15
There is a known bug, which is fixed in CentOS 6.6 and openssl 1.0.1e-16 : https://bugzilla.redhat.com/show_bug.cgi?id=1025598
It's a shoot in the wild but maybe it helps.
If you need further help you have to provide more details to your setting then just posting the error message. Provide at least your OS, Ambari, and HDP version.