Background

First choose what type of check you want to write and in which plugin context the check should be run. The choices are events and scenarios.

Definitions are organised beneath a directory that shares the name of the plugin that will run them and can be grouped using files and directories. All definitions have the same basic structure using a mixture of properties.

This approach provides a way to write checks and analysis in a way that focuses on the structure and logic of the check rather than the underlying implementation. This is achieved by leveraging the properties provided along with libraries/shared code (e.g. core plugins as much as possible).

The yaml definitions are loaded into a tree structure, with leaf nodes containing the consumable information such as checks. This structure supports property inheritance so that globals may be defined and superseded at any level.

In summary:

• Top directory shares its name with the plugin the checks belong to e.g. openstack.

• Sub levels contain definitions which can be organised using any combination of files and directories, using them to logically group your definitions.

• The backbone of this approach is propertree i.e. a tree where each level contains override properties and “content”. Overrides follow an inheritance model so that they can be defined and superseded at any level. The content is always found at the leaf nodes of the tree.

TIP: to use a single quote ‘ inside a yaml string you need to replace it with

two single quotes.

Pre-requisites

If you want to gate running the contents of a directory on a pre-requisite you can do so by putting them in a file that shares the name of its parent directory. In the following example mychecks.yaml contains a Requires and the rest of the directory will only be run if it resolves to True:

$ ls myplugin/mychecks/
mychecks.yaml myotherchecks.yaml
$ cat myplugin/mychecks/mychecks.yaml
requires:
  or:
    - property: hotsos.core.plugins.myplugin.mustbetrue
    - path: file/that/must/exist