Could you share the output of your web browser (not images please but just code formatted text): when you run you application in machine 10.21.8.146
with the following code:
$ hosts = [ '10.21.8.146:9200' ];
and then with:
$ hosts = [ '127.0.0.1:9200' ];
Could you also double check that you did not put spaces as you wrote with:
$ hosts = [ '10 .21.8.146: 9200 ' ];