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Techniques

Templating in YAML

Apr 2019
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As infrastructures grow in complexity, so do the configuration files that define them. Tools such as AWS CloudFormation, Kubernetes and Helm expect configuration files in JSON or YAML syntax, presumably in an attempt to make them easy to write and process. However, in most cases, teams quickly reach the point where they have some parts that are similar but not quite the same, for example, when the same service must be deployed in different regions with a slightly different setup. For such cases tools offer templating in YAML (or JSON), which has caused a huge amount of frustration with practitioners. The problem is that the syntax of JSON and YAML requires all sorts of awkward compromises to graft templating features such as conditionals and loops into the files. We recommend using an API from a programming language instead or, when this is not an option, a templating system in a programming language, either a general-purpose language such as Python or something specialized such as Jsonnet.