jordelver

Is Broadway suitable for this task?

I’ve got a potential project that I think Broadway is well matched for, but I wanted to ask here for a sanity check

The basic workflow is:

Periodically fetch data from a JSON HTTP API
Store / cache the data
Convert data / munge data into another format
Provide data over XML HTTP API

To begin with there will only be one endpoint, but in the future there will be many different sources. Each may have different schedules for fetching data.

If I was doing this in Ruby (my background) I would probably use some sort of background job to fetch and convert the data, and then serve the data via Rails.

One reason Broadway is attractive to me is because it has features like rate limiting, which I can see being useful as this scales.

Would you use Broadway for this?

11 comments

#broadway

4 3685 11

2020-02-17 15:47:37 UTC

First Post!

axelson

Scenic Core Team

Disclaimer: I have never actually used broadway

I don’t think that broadway seems like a good fit since it won’t help you with this piece since the official and unofficial producers all pull from an event stream of sorts:

Currently we officially support three Broadway producers:

    Amazon SQS: Source - Guide
    Google Cloud Pub/Sub: Source - Guide
    RabbitMQ: Source - Guide

Although perhaps someone who’s actually used broadway could offer more guidance.

Post #1

Most Liked

sorentwo

Oban Core Team

I’m extremely biased, but I would use oban. It has periodic jobs, scheduled jobs, retries, resiliency, etc. Broadway is tailored for ingesting high throughout event streams.

Post #2

akoutmos

Author of Build a Weather Station with Elixir and Nerves

I have written a few article/tutorials on Broadway and perhaps those can help inform your decision:
https://akoutmos.com/post/using-broadway/
https://akoutmos.com/post/broadway-rabbitmq-and-the-rise-of-elixir/
https://akoutmos.com/post/broadway-rabbitmq-and-the-rise-of-elixir-two/

I think some more information may be required to better answer your question:

How often are you fetching data from this JSON API?
Is it a singular piece of information that needs to be processed (i.e no benefit from concurrent processing)?
Do you require a message queue to persist messages across deployments of your service?

On the simple side of the spectrum, you could have a simple GenServer with a send_after to do everything that you outlined and just start that process up in your application.ex supervision tree. On the complex side of things, you could run RabbitMQ and Broadway to do your processing, but that depends on the answers to the Qs above . Like others have mentioned, Oban is also a good tool for the requirements that you outlined.

Post #8

chasers

I’ve used Broadway extensively. Have not used Oban.

You can use Broadway to poll you just put stuff in your own producer. So you can totally use Broadway here and it would be great.

With Broadway, you do need to understand the lifecycle of a process and your app if you want to make sure you get every event.

Oban is backed by a database so your state is always there. You don’t have to worry about deploys affecting processes, etc. You sacrifice some throughout for this.

So those are mostly your high level trade offs.

If you’re not super comfortable with gen servers I’d say use Oban. If you need all the throughput use Broadway.

Edit: I should maybe clarify. Broadway won’t do the polling for you. Make your poller and put the results in a queue somewhere (ETS probably) and the have your producer pull from that.

Post #6

Last Post!

jordelver

Thanks @chasers and @sorentwo for this interesting discussion. At the moment, I feel like I’d be more comfortable implementing a solution using Oban mainly because I understand the approach more clearly.

One thing that I like about the Oban is approach is observability. It seems to me that I can look at the state in the database and have a better idea of what is happening. I know Broadway has Telemetry hooks but I’m not sure about how to use those at the moment - that sounds like a totally new topic