Adding an R buildpack to my Ruby on Rails App

I’m migrating from Heroku and my Rails app uses an R script to analyze some data.

On Heroku, I added to my Buildpacks section in the Settings tab.

What’s the equivalent step I need to take over here on Fly? I found the Buildpacks section of the docs but nothing I’ve tried has worked.


I’m not an expert on heroku or buildpacks, but (and don’t scream!) I know a thing or two about deploying Rails apps via Dockerfiles. dockerfile-generator is a Rails generator that will inspect your application and generate a dockerfile.

If what you are saying is that you shell out to an R script, that’s beyond what can be automatically detected and I’d need a hint. If you are willing to give it a try, by tomorrow-ish I could have something like the following working for you:

bin/rails generate dockerfile --add r-base

I was planning on adding that support in the next week or so, but I can do that next if you are interested.

I have a Rake task that includes this line:


output, status = Open3.capture2(Rails.root.join("clusters.r").to_s, stdin_data: csv_input)


#!/usr/bin/env Rscript


data <- read_csv(file("stdin"))


for (k in 2:5)

... and so on

This works on Heroku when I include the R buildpack I mentioned above. But when I try to run this on Fly, I get:

/usr/bin/env: 'Rscript': No such file or directory
rake aborted!

I have verified that once r-base-core is added to the Dockerfile, Rscript is available:

% fly ssh console -C Rscript
Connecting to fdaa:0:d445:a7b:ae:56cc:9309:2... complete
Usage: /path/to/Rscript [--options] [-e expr [-e expr2 ...] | file] [args]

--options accepted are
  --help              Print usage and exit
  --version           Print version and exit
  --verbose           Print information on progress
                      Where 'list' is a comma-separated set
                        of package names, or 'NULL'
or options to R, in addition to --no-echo --no-restore, such as
  --save              Do save workspace at the end of the session
  --no-environ        Don't read the site and user environment files
  --no-site-file      Don't read the site-wide Rprofile
  --no-init-file      Don't read the user R profile
  --restore           Do restore previously saved objects at startup
  --vanilla           Combine --no-save, --no-restore, --no-site-file
                        --no-init-file and --no-environ

'file' may contain spaces but not shell metacharacters
Expressions (one or more '-e <expr>') may be used *instead* of 'file'
See also  ?Rscript  from within R

You’re a bit of a wizard! :slight_smile: I’m not sure how this would be possible, but if I could also define which additional packages to install along with Rscript, that would be helpful. For example, I have to install the “readr” package and all of its dependencies as well.

Is this the package you are looking for? Debian -- Details of package r-cran-readr in bullseye

What I’m suggesting is that you will be able to peruse the following: Debian -- List of sections in "bullseye" and add any of the packages you see there - and as many as you want. If you go to that page and click on “GNU R” you will see a long list of packages. And, yes, any package you select would include the list of dependencies.

Note: I’m not the wizard here. That credit goes to the Debian team.

It is ready to beta test. Functionally complete, docs and tests not yet implemented.

First remove any buildpacks from fly.toml.

Then install/update dockerfile-rails.

  • if this gem is not in your Gemfile already, run bundle add dockerfile-rails --optimistic --group development
  • if this gem is already in your Gemfile, run bundle update

Generate a Dockerfile with r-base-core:

bin/rails generate dockerfile --add r-base-core

The generator will remember packages that you have added, so if you want to add another package, run the command again. You can also specify --add multiple times on one command. If you add something you don’t want anymore, run again with --remove.

When ready, fly deploy.

Nothing against buildpacks - they are magic but opaque. Dockerfiles aren’t magic and very transparent/explicit.

Additional information can be found at the FAQ: Dockerfiles and fly.toml · Fly Docs - this page will be updated soon to document how to add and remove packages.