hosts.ini

[foo]
machine-1.domain.tld port=23
machine-2.domain.tld port=24

output

$ rex -G foo uptime
[2015-05-11 16:45:53] INFO - Running task uptime on machine-1.domain.tld
[2015-05-11 16:45:53] INFO - Connecting to machine-1.domain.tld:23 (root)
[2015-05-11 16:45:54] WARN - Can't connect to machine-1.domain.tld (unable to establish master SSH connection: master process exited unexpectedly)
[2015-05-11 16:45:54] WARN - Error running task/batch: Wrong username/password or wrong key on machine-1.domain.tld. Or root is not permitted to login over SSH. at /home/ferki/perl5/perlbrew/perls/perl-5.20.2/lib/site_perl/5.20.2/Rex/TaskList/Base.pm line 295.

[2015-05-11 16:45:54] INFO - Running task uptime on machine-2.domain.tld
[2015-05-11 16:45:54] INFO - Connecting to machine-2.domain.tld:24 (root)
[2015-05-11 16:45:56] WARN - Can't connect to machine-2.domain.tld (unable to establish master SSH connection: master process exited unexpectedly)
[2015-05-11 16:45:56] WARN - Error running task/batch: Wrong username/password or wrong key on machine-2.domain.tld. Or root is not permitted to login over SSH. at /home/ferki/perl5/perlbrew/perls/perl-5.20.2/lib/site_perl/5.20.2/Rex/TaskList/Base.pm line 295.

[2015-05-11 16:45:56] INFO - Exiting Rex...
[2015-05-11 16:45:56] INFO - Cleaning up...

Rexfile

use Rex -feature => ['1.0'];
use Rex::Commands::Virtualization;
use Data::Dumper;

#parallelism 10;

use Rex::Group::Lookup::INI;
groups_file "hosts.ini";

user "root";
private_key "/home/ferki/.ssh/id_rsa";
public_key "/home/ferki/.ssh/id_rsa.pub";

set virtualization => "Docker";

desc "Get the uptime of all servers.";
task "uptime",
  group => "containers",
  sub {
    my $output = run 'echo $HOSTNAME $(uptime)';
    say $output;
  };