ASP.NET Core Web Api route certain requests to microservice running on other port - asp.net-core

Question

I have created a SPA which has to communicate to various microservices in the backend.
For deployment and latency reasons, we have to make sure, that the frontend only communicates with one endpoint, which then routes to the other microservices internally.
How can i make this work with ASP.NET Core? I looked at Ocelot which provides something quite similar but as i see in the documentation i have to configure the IP adress / hostname under which the backend will be accessed from the client and i don't know this information upfront as this will be determined after deployment (and can be different for every machine, given this service will run on various Edge devices).
Can this be achieved using a simple routing middleware which looks for a certain path in the url (e.g. /api/otherservice), send a http request to the responsible microservice (e.g. http://localhost:1234/api/otherservice) and return the information to the caller?
I am using ASP.NET Core 2.1.
Update: I managed to get ocelot running to apply the desired routing to the downstream microservice. However, the service where i use Ocelot provides routes itself (serving the web app frontend and some other backend api routes).
Does anybody know how i can tell Ocelot to fall back to the routes declared in the service it is running if there is a route which is not contained in ocelot.json (or the other way round, to tell ASP.NET Core to just use ocelot for routes id can't resolve on it's own).
Update 2:
This is my ocelot config which results in an infinite loop:
{
"ReRoutes": [
{
"DownstreamPathTemplate": "/api/tool/{url}",
"DownstreamScheme": "http",
"DownstreamHostAndPorts": [
{
"Host": "localhost",
"Port": 5200
}
],
"UpstreamPathTemplate": "/api/tool/{url}",
"UpstreamHttpMethod": [ "Get", "Post", "Put", "Delete" ]
},
{
"DownstreamPathTemplate": "/{everything}",
"DownstreamScheme": "http",
"DownstreamHostAndPorts": [
{
"Host": "localhost",
"Port": 5100
}
],
"UpstreamPathTemplate": "/{everything}",
"Priority": 0
}
]
}
Omitting the second (catchAll) - route successfully routes to the tool-route, but can't serve routes provided by the ASP.NET Core Service which contains the Ocelot Middleware.

Answer 1

Maybe you want a catch all reroute? Since this type of reroute have the least priority it will only do it if all previous reroutes with higher priority fail:
https://ocelot.readthedocs.io/en/latest/features/routing.html#catch-all
{
"DownstreamPathTemplate": "/{url}",
"DownstreamScheme": "https",
"DownstreamHostAndPorts": [
{
"Host": "localhost",
"Port": 80,
}
],
"UpstreamPathTemplate": "/{url}",
"UpstreamHttpMethod": [ "Get" ]
}
If you don't want this default behavior you can take a look at the priority attribute:
https://ocelot.readthedocs.io/en/latest/features/routing.html#priority
{
"UpstreamPathTemplate": "/goods/{catchAll}"
"Priority": 0
}