Merge pull request #1161 from cloudfoundry-incubator/vladi/adr-bash-ruby

docs: ADR for restricting scripting to ruby and bash

doc/architecture/decisions/005-bash-and-ruby.md

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+# 5. Limit the languages, data formats, and tools used by kubecf
+
+Date: 2020-07-24
+
+## Status
+
+Accepted
+
+## Context
+
+As the project grows in numbers of contributors and lines of code, we want to
+make sure we keep the project readable and accessible by external contributors.
+
+To do this we intentionally restrict the choices in scripting languages, data
+formats, and supporting tools.
+
+These restrictions apply not only to the kubecf.git repo, but also to
+kubecf-tools.git.
+
+## Decision
+
+### Scripting Languages
+
+Only use bash and ruby for scripting and tooling in the KubeCF project.  Ruby
+scripts should be unit-tested if possible.
+
+### Statically Typed and/or Compiled Languages
+
+We do not anticipate the need to write any tooling in a compiled language.
+Should this become necessary, the Go language should be choosen.
+
+### Templating Languages
+
+Using Go `text/template` based templating is preferred whenever possible.
+
+### Data Formats
+
+Configuration data should be stored in YAML or JSON format.
+
+### External Tools
+
+External tools must be available on both Linux and macOS.
+
+Compiled tools should ideally be available as binary downloads from their Github
+releases page.
+
+For tools implemented via scripting languages, tools written in bash or ruby
+should be preferred over tools written in other languages whenever this is
+possible and functionality is not compromised. It is acceptable to use tools
+implemented in other languages if no alternative in bash/ruby exists.
+
+The number of external dependencies should be kept low whenever possible. E.g.
+instead of adding a dependency on `yq` use a combination of `ruby` and `jq` to
+achieve the same results with existing dependencies.
+
+## Consequences
+
+Any other existing scripts should be converted to bash or ruby.