Host multiple Rails apps on the same server

Question

I'm trying to host multiple rails apps for my blog. Kind of like www.blog.com/app1 will have one rails app, www.blog.com/app2 will have another. How do I do it?

Answer 1

Although I agree with downvotes as pointed out by the first comment, I had this problem myself several months ago and actually didn’t even try to solve it as I realized how many implications this has. Existing answers on Stack Overflow address either slightly different or narrower issue so they may use some things mentioned here but don’t elaborate on implications or alternatives, yet there’s an interesting overview (and also other answer to that question). Anyway, I took it as a challenge and dived in.

First, there are multiple approaches depending on your scenario:

1. All applications are code which you maintain – it’s probably the best to explore something called engines. They are like mini RoR applications mountable to certain path within normal RoR application. It has many benefits like sharing the same runtime or simple isolation configured in on place.
2. If there are no AJAX with URL or similar dynamisms or that they are actually AHAH (i.e., asynchronous HTML and HTTP – returning HTML fragments instead of XML or JSON data) which is very natural for Rails although often not used, you can use sophisticated proxy modules like mod_proxy_html which rewrite links inside HTML documents while proxying. Similar modules exist for nginx but are not part of standard distribution.
3. RoR has a configuration option relative_url_root which allows deployment to subdirectories. It’s very fragile and often buggy, many gems or engines break when you use it, so beware. When you get it right, it looks like magic. However, your configuration relating to subdirectory will be scattered throughout different software configs and your code.

I created an example repository while exploring the last option. README should say everything necessary to run the code.

The most important observation from this small project is that when using relative URL root, you almost certainly want to scope all your routes. There are different setups possible, but they are even more complicated (which doesn’t mean they don’t make sense). For examples see the answer with overview mentioned above.
By default (without scoped routes), only asset paths are prefixed with relative URL root, but not action route paths even though it makes URLs generated by helpers useless unless translated by mod_proxy_html or probably more custom solution.

Other important observation, which relates to official guide, code “out there” and answers to similar questions here on Stack Overflow, is that it’s good to avoid forward slash at the beginning of relative URL root. It behaves inconsistently between tests and the rest of the code. Yet it can be used nicely around your code – see scope definition in routes config or dummy controller test case.

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I got to these and other observations by creating two very simple and almost identical Rails 5.2 applications. Each has one action (dummy#action) which has a route scoped to relative URL root. This action, or its view specifically does two important things to verify that everything works:

• it outputs the result of calling root_path helper which shows we have correctly setup URL/path helpers (thanks to scoped route in config/routes.rb)
• it loads static asset which isn’t served by Rails application but directly by Apache HTTP Server and which is referenced by image_path helper

You can see that virtual host configuration has rather extensive list of URLs which shouldn’t be passed via proxy and rely on aliased directories. However, this is application specific and very configurable, so simpler setup with different directory layout is definitely achievable but entirely separate topic.

If you like Passenger and don’t want to use proxying in your HTTP server, you can find more information in their deployment tutorial.