Metatargets, Dependencies and Readonly Services

Metatargets, Dependencies and Readonly Services

This section describes the use of metatargets and readonly services.

Metatargets

The term Metatargets refers to the inclusion of targets from within other targets. Under certain circumstances, for example when creating constructs from many interdependent target files, you may end up not specifying all the dependencies of a service or host in your target files. In this case any services that can not be resolved within the current target automatically become Readonly Services.

Readonly Services

Readonly services are special, because they can not be controlled -- in the sense of a state change -- from YADT. Instead you may only query and display their current status.

Example

Consider the following directory structure:

.
├── all
│   └── target
├── appserver
│   └── target
└── webserver
    └── target

The file webserver/target initially looks like:

hosts:
    webserver.example.com

And the webserver machine contains the following configuration:

services:
    httpd:
        is_frontservice: true
        needs_services: ["service://appserver.example.com/tomcat"]

In this case the tomcat service is located on the remote machine appserver and since the target file contains only the host webserver the tomcat service is now readonly.

Next, let's have a look at the appserver target file, that contains the missing host:

hosts:
    appserver.example.com

You can then use the metatargets feature to include both targets from the target file in the all/target:

includes:
- webserver
- appserver

In this case, the tomcat service will not be readonly, since the target includes both the webserver and the appserver and so also the tomcat service that the httpd service depends on.