# Adding a new buildpack to repo2docker

A new buildpack is needed when a new language or a new package manager should be
supported. Buildpacks need to work together. For example, when adding support for
a new language, like nodejs, the new nodejs buildpack should be able to co-exist
with Python / R / etc support.

## Criteria to balance and consider

Criteria to balance are:

1. Maintenance burden on repo2docker.
2. How easy it is to use a given setup without support from repo2docker natively.
   There are two escape hatches here - `postBuild` and `Dockerfile`.
3. How widely used is this language / package manager? This is the primary tradeoff
   with point (1). We (Binder / Jupyter) team do not want to make new formats
   as much as possible, so ideally we can just say 'X repos on binder already use
   this using one of the escape hatches in (2), so let us make it easy and add
   native support'.

## Adding libraries or UI to existing buildpacks

Note that this doesn't apply to adding additional libraries / UI to existing
buildpacks. For example, if we had an R buildpack and it supported IRKernel,
it is much easier to
just support RStudio / Shiny with it, since those are library additions than entirely
new buildpacks.