(R)?ex Deployment & Configuration Management


Deprecating official Rex packages

As part of our efforts to simplify maintenance around RexOps projects, we have decided to stop building Rex packages on our side. We recommend relying on OS packages maintained by the various distributions in their respective upstream repositories, or to install Rex from CPAN.

Post-migration updates & clean-up

Over the course of the past weeks many clean-ups have been done, reaping the benefits provided by our new Statocles-based site:

New site engine for rexify.org

After months of work on a new site backend, we reached the MVP today for our site to be switched over to a new engine: from now on, our site will be maintained using the static site generator Statocles.



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Professional support is also available.

» Home » Docs » Rex book » The rex dsl » Grouping servers

Grouping servers

Rex offers you a powerful way to group your servers. The simplest way to use groups is to just define a group name and add all your desired servers to this group.

⁠group frontends => "frontend01", "frontend02", "frontend03";
⁠group backends  => "backend01",  "backend02";

Rex offers also a simple notation to define server ranges, so that you don't need to type so much.

⁠group frontends => "frontend[01..03]";
⁠group backends  => "backend[01..02]";

This notation will just expand to frontend01, frontend02 and frontend03 for the frontends group and to backend01 and backend02 for the backends group.

Custom parameters for servers are possible with a slightly enhanced syntax since version 0.47:

⁠group frontends => "frontend01" => { user => "bob" },
⁠  "frontend02"  => { user       => "alice" },
⁠  "frontend03";

Because the Rexfile is a Perl script you can just use more advanced things like querying a database, ldap or your dns.

To add your groups to the tasks you have to use the group option within the task generation.

⁠task "mytask",
⁠  group => "mygroup",
⁠  sub {
⁠  # do something  };

If you need to define multiple groups for a task, you can just use an array.

⁠task "mytask",
⁠  group => [ "mygroup", "mygroup2" ],
⁠  sub {
⁠  # do something  };

Using an INI file to define server groups

Rex offers a simple way to query ini files for group creation. To use ini files you have to use the Rex::Group::Lookup::INI module.

use Rex -feature => ['1.0'];
⁠use Rex::Group::Lookup::INI;
⁠groups_file "/path/to/your/file.ini";

Rex expects the following format inside your INI file.



Rex also offers a little bit advanced functions for the ini file. You can define custom parameters for each server or include groups inside groups.

frontend02 user=root password=f00bar auth_type=pass maintenance=1



These additional options (in this example maintenance can be queried with the option method from the connection object.

⁠task "prepare",
⁠  group => "frontends",
⁠  sub {
⁠  if ( connection->server->option("maintenance") ) {
⁠    say "This server is in maintenance mode, so i'm going to stop all services";
⁠    service [ "apache2", "postfix" ] => "stop";
⁠  }
⁠  };

Quering a database to define server groups

If you want to get your server groups right out of an existing database you can use DBI to connect to your database server. In this example you will learn how to connect to a MySQL database and to get the hosts out of a table.

use Rex -feature => ['1.0'];
⁠use DBI;
⁠my $username = "dbuser";
⁠my $password = "dbpassword";
⁠my $database = "hostdb";
⁠my $hostname = "mysql.intern.lan";
⁠my $port     = 3306;
⁠my $dsn      = "DBI:mysql:database=$database;host=$hostname;port=$port";
⁠my $dbh      = DBI->connect( $username, $password );
⁠my $sth = $dbh->prepare("SELECT * FROM hostlist WHERE enabled=1");
⁠my %server_group = ();
⁠while ( my $row = $sth->fetchrow_hashref ) {
⁠  my $group_name  = $row->{server_group};
⁠  my $server_name = $row->{server_name};
⁠  push @{ $server_group{$group_name} }, $server_name;
⁠map { group $_ => @{ $server_group{$_} }; } keys %server_group;

This example expects the following column names:

Creating custom groups

If there is no built-in function that fits your needs for group creation, you can do it all by yourself. Because the Rexfile is just a plain perl script and the group command is just a perl function that expects the group name as first parameter, and uses all other parameters for the servers, you can create your own function.

my @list = ( "some", "list", "entries" );
⁠group mygroup  => grep { /list/ } @list;
⁠group myserver => map  { "s$_.domain.com" } qw(1 3 7);
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