Adding node.js to your Phoenix Dockerfile for fly.io

June 15, 2023

Updated 2023-11-11 after this dumpster fire of a migration happened. See here for the previous version.

For some projects, avoiding the JS ecosystem just isn't possible. If you ever find yourself needing to add npm modules to your Phoenix app hosted on fly.io, here are the changes required to ensure your build step works.

Assumptions

Note that this guide assumes you've already run npm init in the assets directory of a Phoenix project.
The guide also assumes that you have the associated Dockerfile and supporting changes from running fly launch to host your app on https://fly.io in your project.

Step by step

curl is included as a dependency to be installed in the apt-get call.

RUN apt-get update -y && apt-get install -y build-essential git curl \
     && apt-get clean && rm -f /var/lib/apt/lists/*_*

Install node and npm

RUN apt-get update && apt-get install -y ca-certificates curl gnupg
RUN mkdir -p /etc/apt/sources.list.d /etc/apt/keyrings
RUN curl -fsSL https://deb.nodesource.com/gpgkey/nodesource-repo.gpg.key | gpg --dearmor -o /etc/apt/keyrings/nodesource.gpg
RUN echo "deb [signed-by=/etc/apt/keyrings/nodesource.gpg] https://deb.nodesource.com/node_20.x nodistro main" | tee /etc/apt/sources.list.d/nodesource.list
RUN apt-get update && apt-get install nodejs -y

Finally, node modules are installed from npm to make sure they're available for the build step.

RUN npm install --prefix assets
#...
# The above needs to be run before this step
RUN mix assets.deploy