Ability to proxy unhandled requests to an upstream server

[cameronbraid]

moved from #68

I'm looking for a self hosted solution for SSR/DSG and came across this plugin. It seems to address most of my needs, however one thing I need is the ability to proxy unhandled requests to an upstream server.

Currently I am using gatsby 3 without ssr/dsg. I build a docker image using nginx. I use a plugin that generates explicit location directives for each index.html file, static file, and gatsby redirects, plus a final wildcard proxy_pass directive to send the remainder of the traffic upstream.

In order to switch to this plugin, I would need to make the following changes to this plugin:
a) in handleDsgSsr if the request is not for a page then make the handler fall through to a later handler (is this possible in fastly?)
b) in gatsby.ts allowing configuration of FastifyPlugin to be configured before handle404 where I can configure a proxy

[cameronbraid]

Hey Cameron, I'm headed out on vacation this week so not sure how much thought I can give this before early November. Here's what comes to mind immediately.

1. Could you please start a discussion thread with this info where we can discuss this apart from the v4 pr.

2. I was just thinking today that I don't actually need to use wild card routes for ssr/dsg. I need to confirm that, but might make this easier to implement.

3. I'm not convinced this should be the concern of this server. Seems like something a reverse proxy, like fastly or nginx, should handle. Not against it outright, just want to make sure it's a good move.

4. Seems like this could make 404 handling a interesting. 🤔

Originally posted by @moonmeister in #68 (comment)

[cameronbraid]

re (4) : 404 is no issue as the upstream server will have a 404 handler. This site is a migration from a custom express app where only some of the URLs are handled by gatsby (and more as they get migrated across)

re (3) :

I could configure the nginx server to proxy every gatsby URL to Fastify and its fallback to proxy to my custom express server. However I think that Fastify can do everything that nginx does so its one less component to deploy, monitor and manage.

I'll have a play with your Fastify branch and see what I can come up with.

[cameronbraid]

I should also note that I also already have a envoy edge proxy which does ssl termination etc.. (via istio)

[cameronbraid]

@moonmeister Since you just changed SSR/DSG to explicitly map the pages to routes in #68 it should be straightforward now to handle my case by replacing the 404 handler with a proxy

[moonmeister]

That would work with a custom implementation. I was also thinking we could possible implement a way to do that programmatically vs you having to do a complete custom implementation but I have a lot of other things I want to ship first.