This post goes through how to set up a one-way sync of a local python package to a Google Colab instance using cloudflared, lsyncd and some jupyter magic. This allows you to work on a package locally in your IDE of choice and have it automatically stay in sync with the version imported into your notebook. Within a couple of seconds of making a change locally, your changes are auto-reloaded into your running notebook without having to re-import anything. This example is focusing on using a python package but that’s not a requirement. Ultimately we’re just syncing a local directory to a remote one so this could be used in various ways, eg. syncing config files that you want your notebook code to pick up.

One time setup

You will need to install cloudflared and lsyncd on your local machine.

cloudflared is used to easily set up an ssh tunnel between your machine and the google colab instance
lsyncd is used to detect local file changes and sync them to the target using rsync (in this case with rsyncssh)

Install cloudflared and lsyncd:
```
sudo apt-get install cloudflared lsyncd
```
Refer to the project github pages for alternative installation options.

Next add this to your ~/.ssh/config

Host *.trycloudflare.com
    HostName %h
    User root
    Port 22
    ProxyCommand /usr/local/bin/cloudflared access ssh --hostname %h

Replace the /usr/local/bin/cloudflared with the absolute path to cloudflared if installed elsewhere.

On each notebook run

Each time you run a notebook, you will need to set up cloudflared on that machine. Thankfully, colab-ssh is a package that handles all this for you.

In your notebook, simply run:

!pip install colab_ssh --upgrade

from colab_ssh import launch_ssh_cloudflared
launch_ssh_cloudflared(password='<SSH_PASSWORD_HERE>')

This will return an ssh command like this:

ssh <CLOUDFLARE_PREFIX>.trycloudflare.com

Next, you’ll want to add your ssh key to the remote ~/.ssh/authorized_keys. From your local, run:
```
ssh-copy-id <CLOUDFLARE_PREFIX>.trycloudflare.com
```
You should now be able to ssh into the colab instance without a password.

Now we can start up lsyncd. You need to specify the source and target directories. From your local, run:

lsyncd -nodaemon -delay 1 -rsyncssh <SOURCE_DIR> <CLOUDFLARE_PREFIX>.trycloudflare.com /<PACKAGE_NAME>

For example:

lsyncd -nodaemon -delay 1 -rsyncssh /home/lucas/repos/demo_package training-eggs-others-criminal.trycloudflare.com /demo_package

Finally, back in the notebook, run:
```
import sys
sys.path.insert(0, '/<PACKAGE_NAME>')

%load_ext autoreload
%autoreload 2

import <PACKAGE_NAME>
```
When you import your package into the notebook, it will be pointing at the synced directory. Whenever you make changes locally, they are synced to colab, and when you next run a cell, colab will reload the package with all the updates.