Now, hold on, stop to read and think again about what we've seen in this chapter, and particularly in the last section: variables that define our infrastructure can be dynamically populated according to the number of hosts that have specific classes or resources. If we add hosts with these services, they can be automatically used by the other hosts.
This is what we need to configure with Puppet dynamic and elastic environments where new services are made available to other nodes which are consequently configured.
For example, to manage a load balancer configuration, we can use, in the ERB template that is used for its configuration, a variable that returns all the IP addresses of the nodes that have Apache installed:
$web_servers_ip = query_nodes('Class[apache]', ipaddress)This is a simple case that probably doesn't fit real scenarios where we probably have different Apache web servers doing different works in different servers, but it can give us an...