MargoAPI.jl

Interactive web-based articles for ClimateMARGO.jl

Have a look at our Observable page!

Backend

This repository contains the "backend" for our interactive articles written in Observable. It imports the ClimateMARGO.jl package, and wraps its important functionality in API functions.

This repository is deployed online using heroku. See the API client notebook to learn more.

Technology

Powering this API is a super fast & simple web framework for Julia. Write functions that take keyword arguments and return simple objects.

@expose function wow(;a, b)
    Dict(
        :sum => a + b,
        :diff => a - b,
    )
end

You can then use them inside JavaScript:

sendreceive("wow", {
    a: 7,
    b: 6,
}).then((val) => {
    console.log(val.sum)
    console.log(val.diff)
})

It was created by stripping down Pluto.jl to just its communication code.

Features

It uses WebSockets for optimal ping time (2ms on localhost) and MessagePack for minimal (de)serialization overhead and minimal bandwidth usage. (A round trip to a Julia function returning a 1M-element Array{UInt8} is about 20ms - you could stream uncompressed 512x512 images at 60fps 😮.) We also have automatic timeout and reconnect.

Heroku deployment

Updating the deployment

We currently have two deployments:

• master (link to app), link to heroku for Fons & Henri);
• staging for the WIP latest updates (link to app, link to heroku for Fons & Henri).

These correspond to two branches of this repository with the same names.

To update the web app at heroku, we simply push a commit to the branch. The

For more background on deploying Julia apps on heroku, I wrote this guide, intended for a more general audience: fonsp/How to put Julia on heroku.md .

Creating a new deployment

Read the guide above for some basics. Some notes specific for this project:

• You need to set a "Config Var" in the Settings page of your heroku app: JULIA_MARGO_LOAD_PYPLOT with value nothanks. Trigger a rebuild afterwards by committing. more info
• We tried to minimize Julia's compile time for the first request, but you will still benefit from using a "Hobby Dyno" (7$/month) instead of a free dyno.

Running locally

Clone the repository, navigate to this folder, and then:

julia --project run_server.jl 127.0.0.1 2345

Then go to http://localhost:2345/index.html in your browser. This is only really useful to check for errors, since it does not include the visualisations. To connect an observable notebook to a local running instance of the server, you can use ngrok. In a second terminal, install ngrok and run:

./ngrok http 2345

You can then change the cell margo_url in the notebook to the https url that gave you, instead of the default. Contact me (fons) for more info.

Contact

If any of this is interesting to you, get in touch!

— Henri Drake (hdrake) & Fons van der Plas (fonsp)