Mosa

parser

Converts a number of files into a raw AST. For instance, if we load the following manifest, the AST will look exactly like it, with all variables and everthing intact. Only syntax is checked. This means that the manifest may still be invalid; undefined variables may be referenced, undeclared types may be realized, cyclic dependendencies are allowed, etc.

node 'localhost' {
	class { 'webserver':
		wwwdir => "dev.local",
	}
}

class webserver($wwwdir,) {
	package { 'nginx': }
	
	file { "/etc/nginx/sites-available/server.conf":
		content => "
			server {
				root '$wwwdir'
				location / {}
			}
		", 
	}
}

define single package($name,) {
	exec { "apt-get install $name": }
}

define single file($name, $content,) {
	exec { "cat > $name":
		stdin => $content,
	}
}

resolver

The resolver resolves all declarations in the manifest and returns them. The declarations returned will all have concrete values. This gives us a definition of how the final state of our target system should look like.

After our AST above has been run through the resolver, the following will be returned:

exec { 'apt-get install nginx': }

package { 'nginx': }

exec { 'cat > /etc/nginx/sites-available/server.conf':
	stdin => '
		server {
			root 'dev.local'
			location / {}
		}
	',
}

file { '/etc/nginx/sites-available/server.conf':
	content => '
		server {
			root 'dev.local'
			location / {}
		}
	',
}

reducer

Now that we have a clear image of what the final state of the target system should be, it's time to run the reducer. The reducer helps us find out which declarations are already fullfilled in the target system. With this knowledge, we can remove those declarations from the manifest, as we need no action to reach them.

If we for example's sake suppose that /etc/nginx/sites-available/server.conf already exists on the target system, and has the content specified, our declaration list would look like the following after the reducer has been invoked:

exec { 'apt-get install nginx': }

package { 'nginx': }

stepconverter

After the facter has been invoked, we only have a subset of our original declarations that we need to actually execute. The stepconverter converts these into a number of concrete steps with dependencies between them. As exec is the only builtin type in mosa, all defines result in a number of exec declarations. It's these declarations that are converted into steps, while everything else is thrown away:

exec { 'apt-get install nginx': }

planner

The planner resolves the dependencies between the steps that we need to execute, and groups them into a number of stages.