Development environment setup

We use a bunch of tools while developing Reahl itself. Some are just useful, some enable remote pair programming, and others make sure our tests consistently run the same way.

To ensure things always work, and always work consistently, we employ Vagrant with our own Vagrant box with all of these pre-installed and configured.

If you just want to develop on your own project (even if it does not use Reahl), you can still use the same tools as we do.

It may take some extra effort to set up and learn Vagrant if you don’t know it already, but it is well worth it.

The Reahl Vagrant box

The Reahl vagrant box is called ‘reahl/bionic64’[1], to use it put the following in your Vagrantfile: = "reahl/bionic64"

Reahl already has a correct Vagrantfile in the root of its source tree. A project using Reahl can use the vagrant/Vagrantfile.example file as starting point.

Inside the Vagrant box

Inside the Vagrant box, we have:
  • Projects installed that Reahl depends on;
  • A postgresql database with the vagrant user set up as administrator;
  • A Python3 virtualenv prepared for Reahl development;
  • A version of chromium-browser that works well with tests;
  • A matching version of chromedriver to enable selenium tests;
  • Various ways to access the GUI on the Vagrant machine; and
  • Configuration for pip to allow local installation of what is built (useful for tox tests).

Running the tests

You should be able to run tests immediately:

vagrant up
vagrant ssh
cd /vagrant
reahl shell -sdX reahl unit

The last command changes into the directory of each separate Reahl component, and run its tests in turn.

Browsers and seeing stuff

We use an Xpra display server for the Vagrant machine. It allows headless operation and sharing of GUI windows for pair programming.

When you run tests a per above instructions, the browser is fired up headless on DISPLAY :100.

An xpra display server is automatically started on :100 when you vagrant ssh.

If you are working alone and would rather see what is happening, you can bypass the headless server by forwarding your local X display server. Do this by entering vagrant like so:

vagrant ssh -- -X

The webserver ports of the Vagrant box are forwarded to your local machine. Thus, you need not make use of the browser inside the Vagrant box to check things out. You can use your own, on your own machine: if you have a webserver running inside vagrant on port 8000, you can visit it by surfing to http://localhost:8000

Editing code

There’s no IDE installed inside the Vagrant machine. You need to install and configure one of your choosing on your own machine. You need to use an IDE that is able to connect to a remote host (the Vagrant machine is “remote” from the perspective of an IDE). Your IDE also needs to be able to work with Python code inside a specific virtualenv on the remote host.

To know to which machine to connect your IDE, run (on your own machine):

vagrant ssh-info

To know which virtualenv to connect to, ssh into the Vagrant machine, and run:


Pair programming

We often pair program remotely. Doing this requires a bit more know-how. Here’s how we do it:

Lets assume John and Jane want to work together, and decide to do so on Jane’s computer. In order to do this, Jane needs to expose her Vagrant machine on the Internet and allow John to log into it. From there on, John can share various things with Jane via an ssh connection to Jane’s Vagrant machine.

From a security point of view, Jane never puts her real workstation at risk of tampering by John.

Install reahl-workstation on your development machine

The reahl-workstation component of Reahl is meant to be installed separately on your own development workstation. It contains the reahl commandline and a few commands that are useful for pair programming.

If you are on ubuntu install it like this:

(The rest of this text assumed that you have reahl-workstation installed.)

Use ngrok to expose the Vagrant machine

We use ngrok to make a local Vagrant machine accessible on the Internet to all the tools we use.

Jane must have an account at ngrok, and share her Vagrant machine.

In order to setup ngrok, download it–our scripts expect its executable to be in ~/bin. Follow the instructions on the ngrok website to create an account and save your credentials locally.

To share a locally running Vagrant machine (assuming ngrok is all set up), Jane can then run reahl ngrok start -V from the root directory of the Reahl source. This command will provide output in the form of a DNS name and port number that the remote party can use to access. Make a note of these for use later on.

Let the remote user connect securely

We do not allow login via password for security reasons [2]. For John to be able to log in, his ssh public key needs to be installed into Jane’s Vagrant machine. To do this, John should send his public key to Jane. John’s public key is in ~/.ssh/ on his computer.

To enable John to log in, Jane edits the /home/vagrant/.ssh/authorized_keys file on the Vagrant machine and append the contents of John’s public key to whatever’s in that file already.

Now John will be allowed in. John also needs to make sure when connecting that he is connecting to the correct machine and not some impostor. When Jane logs into her Vagrant machine via vagrant ssh, the various fingerprints belonging to the Vagrant machine are printed out in various formats. Jane should send this to John.

John can now ssh as the user called vagrant to the host and port reported to Jane when she started ngrok. John will be presented with one of the fingerprints of the machine he is connecting to. This fingerprint should match one of the ones Jane sent earlier. If it matches, John can say ‘yes’ to ssh, which will now remember the fingerprint was OK, and not ask again.

Sharing a terminal with screen

Gnu screen is a program used to share a terminal between two people. It is configured for this use on the Vagrant machine.

One user starts a screen session by doing (on the Vagrant machine):


The other connects to the same screen session by doing (on the Vagrant machine):

screen -x

Now both can see and type on the same terminal.

Sharing a browser with xpra

It is useful for both users to also see the same browser window also, for example, when debugging JavaScript issues using in-browser tools.

If Jane logs into the Vagrant machine using only vagrant ssh (ie, no – -X argument), an xpra display server is automatically started on the Vagrant machine and all GUI programs will be displayed there.

In order to see that GUI, both Jane and John need to connect to it. It is often very useful NOT to connect to it, because its not very interesting to see the tests execute. In some circumstances (such as debugging) you do however want to see what is going on.

Jane and John need to have xpra and reahl-workstation installed on their own machines for this to work.

Jane connects by running (on her own machine, from within the root of the Reahl source code): reahl xpra attach -V

John connects via ngrok using the machine name and port number provided earlier:

reahl xpra attach -s [email protected] -p 19837

Editing code together

To edit code collaboratively, we use floobits. Floobits is a hosted service, which provides plugins for various IDEs to allow such collaborative editing from your own IDE. It also allows editing on the web.

[1]We develop on the latest LTS version of Ubuntu.
[2]Once you expose a Vagrant machine to the Internet, malicious parties will discover it and start trying user name and password combinations to try and log in. We configured the Vagrant machine to disallow password access via ssh altogether to guard against such attacks. What password would we have used out-of-the-box anyway?