absolutize-links

A bash script to convert relative node_modules symlinks to absolute ones, so we can use with docker volumes.

This repo was created in tandem with this issue comment: https://github.com/npm/npm/issues/14325#issuecomment-285566020

installation

npm install -g absolutize-links

purpose

When you run npm link, what it's doing under the hood is creating a symlink from . to /usr/local/lib/node_modules. On the other side, when you npm link package-name, it creates a link from node_modules/package-name to /usr/local/lib/node_modules/package-name.

If you were to run docker run --rm -it your-image-name:latest ls -al node_modules | grep -e "->", you'll likely see something like this:

package-name -> ../../../../../../usr/local/lib/node_modules/package-name

It's very unlikely that there's anything at all in your docker container at that path, which is why npm is telling you that file doesn't exist - it's right, it doesn't!

the problem

Unfortunately AFAIK npm doesn't allow you to create non-relative symlinks with npm link, which is problematic in that the directory structure of your docker container is pretty much never going to be the same as the directory structure of your local laptop.

In addition, since nothing is copied from /usr/local to the image, even if your directory structure were to match, the file still wouldn't exist.

a complex workaround, aka how to use this lib

Because npm link makes relative symlinks, and because docker doesn't allow using volumes outside of $HOME by default, I can't think of a solution that doesn't require modifying your local fs and docker settings.

However, here's one way:

1. Update Docker for Mac settings to include /usr/local/lib/node_modules in the shared folders so you can use it as a volume:

2. Update any local symlinks to be absolute. Link them using npm link package-name, then run this script (absolutize-links)

3. Add a volume to your docker config:

To run a docker command, add a -v /usr/local/lib/node_modules:/usr/local/lib/node_modules - this will mount your local npm node_modules on your docker container, which will make them available. You'll unfortunately also need to add a -v flag referencing the local linked modules' folder.

If you're using docker-compose, you can add these entries as volumes keys in your docker-compose.yml, so they'll always be there when you restart your container.

There's quite a lot of nuance when it comes to setting up docker volumes, so I'll leave it at the above for now, but the idea here is that you'll need both /usr/local/lib/node_modules and /path/to/the/linked/module defined as volumes when you run your docker image.

usage

absolutize-links [node_modules_dir]

node_modules_dir defaults to node_modules, so if you're in the same directory as package.json, you should be fine running just absolutize-links.