A team at my workplace uses Jsonnet for this problem and it seems to work very well. It's a nicely human-readable DSL for generating JSON in a way that respects JSON structures - you can construct lists of objects (deployments, services, etc.) by looping over templates and composing modifications.

That seems a lot better than either SaltStack's use of Jinja (using text-based templating on a structured format) or Ansible's (using YAML as syntax for an imperative programming language that has Jinja-evaluation functionality).