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rdockershinyshiny-servershinyproxy

Will Docker suffice for a Shiny app with ~100 connections or do I need Shiny Proxy?

I'm looking for a free and open source option for serving out a Shiny appl to ~100 of my students simultaneously. I tried to do this with Shiny Server Open and it throttled. Users got a message like

Too Many Users

Sorry, but this application has exceeded its quota of concurrent users. Please try again later.

After searching on that error message I now know that I can increase the number of concurrent connections, but I'm afraid of bottlenecks due to R's single threaded-ness. I'm aware of Shiny Proxy and I've been experimenting with this, but it seems like it may contain an extra layer of complexity that I don't need.

I've served Shiny apps before with Docker (but not to this large of an audience), so I'm wondering if it will be sufficient.

My question is this: if I don't need authentication (user logins), will Docker suffice for a single page application for ~100 simultaneous connections? Or do I really need Shiny Proxy?

Corollary: how can I test this and ensure that it will work (outside of getting in front of a 100 student class and testing on the fly)?

Solution

    • Do you care if they all share the same underlying R process?

      The open-source version of shiny-server allows you to serve apps, but they all share a single R process. So if your app has a long-running simulation, while one user runs that, it would tie-up your R thread and block the other users until it finishes running.

      I don't know that there is a limit on the concurrent connections, if you don't mind them sharing the R process as described above. You can try increasing the simple_scheduler setting, see Section 3.1.2 Simple Scheduler, in the documentation for shiny-server.conf (typically at /etc/shiny-server/).

    • If you don't care about them all being at the same URL, you could just use multiple instances of the open-source shiny-server, for instance in docker containers hosted on your machine at different ports.

    • If you want to do something like load-balance between instances of your application (horizontally scaling behind a single URL), you'll need either shiny-server pro, ShinyProxy, or to use a load balancer with sticky-sessions. This is because shiny apps handle state in-memory in a R session, so if you try to send your students to a URL and that URL is backed by n instances of your app, but there is no stickiness guarantee, than an individual student's action will not necessarily be on the same instance each time, and the apps won't work as you expect.

      Shiny-Server pro and ShinyProxy handle this stickiness for you with cookies and headers. Depending on your cloud-services provider, they probably support a browser cookie which would work as long as you don't need your students to be able to open multiple tabs of your app with different instances.