An introduction to Rex - FLOSS UK DevOps York 2015

(R)?ex
Deployment & Configuration
Management
Andy Beverley
andy@andybev.com

Contents
● Introduction
– Why this talk
– What is Rex
● General features
● Why I use Rex
● Installation
● General examples
● How I use Rex

Why this talk?
● Rex not as well known as other orchestration
tools
● I'm a recent convert - spread the word!

What is Rex?
● "Remote Execution"
● Easily run batched commands remotely
● Similar in concept to Ansible (push not pull)
● Start with Rexfile (Makefile)
● A Rexfile contains tasks

General features
● Group by server type
● Very flexible scripting (Perl)
– Minimal Perl knowledge required
– Strength and a weakness?
● Many modules, or add your own (to core?)
● Augeas interface
● Transactions and rollback
● Store config in database

Why I use Rex
● Community not commercial
● Very helpful maintainers and mailing list
● Fast merges for PRs
● Very active project
● Flexible

Installation
● Packages available for most distributions
● Or:
– cpan Rex

Example Rexfile
set connection => "OpenSSH";
user "root";
private_key "~/.ssh/id_rsa";
public_key "~/.ssh/id_rsa.pub";
key_auth;
task "say_uptime", sub {
say run "uptime"
};

Running a Rexfile
$ rex say_uptime
$ rex -H myhost say_uptime

Updating packages
use Rex::Commands::Pkg;
task "upgrade", sub {
update_package_db;
update_system;
};
● Tasks can be contained in your own common modules

Installing and configuring
task "setup_ntp", sub {
install "ntp";
};

pkg "ntp", ensure => "latest";
service ntp => ensure => "started";
};

file "/etc/ntp.conf",
source => "files/etc/ntp.conf";
};

source => "files/etc/ntp.conf",
owner => "root",
group => "root",
mode => 644;
};

source => "files/etc/ntp.conf",
owner => "root",
group => "root",
mode => 644,
on_change => sub {
service ntp => "restart"
};
};

File command
file "/etc/hosts",
content => template("templates/etc/hosts.tpl"),
owner => "user",
group => "group",
mode => 700,
on_change => sub { say "Something was changed." };

File command
file "/etc/named.conf",
content => template("templates/etc/named.conf.tpl"),
no_overwrite => TRUE;

File command
file "/etc/motd",
ensure => "absent";
delete_lines_matching
"/var/log/auth.log" => "root";
append_if_no_such_line
"/etc/groups", "mygroup:*:100:myuser1,myuser2";
append_or_amend_line "/etc/groups",
line => "mygroup:*:100:myuser3,myuser4",
regexp => qr{^mygroup};

Server groups
group web_servers =>
"web1", "web2", "web3";
group web_servers => "web[1..3]";
group servers =>
"web[1..3]", "db[01..02]", "mail";

Server groups
task "uptime", group => "web_servers",
sub { say uptime; };

Augeas interface
augeas modify =>
"/files/etc/postfix/main.cf/myhostname"
=> "myhost",
"/files/etc/postfix/main.cf/relayhost"
=> "smtp.isp.com";

Augeas interface
augeas modify =>
"/files/etc/postfix/main.cf/myhostname"
=> "myhost",
"/files/etc/postfix/main.cf/relayhost"
=> "smtp.isp.com",
on_change => sub {
service postfix => "restart";
};

Transactions
task "do-something", "server01", sub {
on_rollback {
rmdir "/tmp/mydata";
};
transaction {
mkdir "/tmp/mydata";
upload "files/myapp.tar.gz", "/tmp/mydata";
run "cd /tmp/mydata; tar xzf myapp.tar.gz";
if ($? != 0) {
die("Error extracting myapp.tar.gz");
}
};
};

How I use Rex
● Central configuration database
● Extract server groups from database
● Set of "base" tasks
● Other tasks depending on server type
$ rex -H newserver web_server

How I use Rex
include qw/
Common::SSH
Common::Web
/;
task "base", group => "base", sub {
Common::SSH::clampdown();
};
task "install_gads", group => "gads_servers", sub {
base();
Common::Web::install_app(
base_domain => 'ctrlo.com',
cert_domain => 'gads.ctrlo.com',
);
};

Config from database
use JSON;
my $groups = json_decode(
`configdb.pl --type server --action summary`
);
foreach my $group (@$groups) {
my $type = $group->{type};
my @servers = @{$group->{servers}};
group $type => @servers;
}
task "setup_apache", group => "web", sub {
...
};

Certs from database
use Rex::Commands::File;
use IPC::Run3;
use JSON;

Certs from database
my $certs = decode_json(
`configdb.pl --type cert --server $hostname`
);
foreach my $cert (@$certs) {
if ($cert->{type} eq 'key') {
my $key = $cert->{content};
my $out;
run3 "openssl rsa -passin pass:'$pass'", $key, $out;
file $cert->{filename},
content => $out,
owner => "root",
group => "ssl-cert",
mode => 640,
on_change => sub { ... }; # e.g. restart web server
}
}

www.rexify.org
Andy Beverley
andy@andybev.com

An introduction to Rex - FLOSS UK DevOps York 2015

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