In this blog post we show how it is possible to run an arbitrary program, script, or execute arbitrary code in reaction to changes and generally events in a PostgreSQL database.
Triggers Database management systems (DBMS) provide mechanisms for defining reactions to certain actions or, in other words, for defining that specific actions should trigger specific reactions. PostgreSQL, the DBMS used by CFEngine Enterprise, is no exception. These triggers can be used for ensuring consistency between tables when changes in one table should be reflected in another table, for recording information about actions, and many other things. PostgreSQL's Overview of Trigger Behavior describes the basics of triggers with the following sentences:
This blog post will focus on the bash programming part of implementing a promise type. To understand what custom promise types are, and how to use them, you should read the introduction first.
To implement a custom promise type in CFEngine, you need a promise module. The module is an executable, and can be written in any language. It’s possible to write one from scratch, but to make it as easy as possible, we decided to provide libraries for common programming languages. In our previous blog post, we showed how to implement modules in Python. That’s great, it’s a powerful, expressive and readable programming language, however there is one drawback; installing python. Many systems don’t have python already, or have a version which is too old. So you will need to add policy to install / update Python, to make sure modules work correctly everywhere.
