I'm constructing a template to build a configuration file, and the service that consumes this file places constraints on identifier lengths.

If an identifier is longer than, say, 6 characters, the service will get part-way through applying the configuration, fail, and leave the node in an inconsistent state.

How can I perform an assertion to trigger a deployment transaction failure, preventing the target nodes' service from being misconfigured?

My particular circumstance is Salt, but I would be curious to see how other systems solve the problem as well.

  • Well in chef I'll add a linting rule, either rspec or foodcritic or ensure the identifier match in the recipe. No idea for salt, I don't think there's a gerenic answer as each configuration manager has its own specificity
    – Tensibai
    Commented Apr 24, 2017 at 20:55
  • I'll edit the answer to be a bit less specific. Commented Apr 24, 2017 at 20:58
  • At the moment, my current contemplation for a Saltstack+Jinja solution would be a macro that attempts to read from a file that cannot exist. Other renderers would work differently. A Python renderer, for example, would be trivial; simply throw an exception. Commented Apr 25, 2017 at 16:42

1 Answer 1


In Ansible: you can use assert or fail module.

- name: "Make sure web_sites is dictionary"
  fail: msg="web_sites should be dictionary"
  when: web_sites is not dict  

- name: "cluster_name should be shorter than 6 chars"
       that: cluster_name|len <= 6

In Puppet: there is fail function evaluated during parsing phase which cause parsing failure on server (see question on StackOverflow)

 if length($cluster_name) > 6 {
      fail("Cluster name is too long. Should be less than 6 chars.")

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