Why are these Swagger endpoints behind a reverse-proxy not found? - nginx

Question

I have a small number of ASP.NET Core services, all running in Docker (via Docker Compose). All services are currently using a prefixed route (their own service name). And they're all setup in Docker Compose to use their own service name as their hostname (connectivity between service containers is OK).
The /api-docs endpoint is provided by Swashbuckle; we setup the prefixed route here, too.
app.UseSwagger(options =>
{
options.RouteTemplate = "scheduler/api-docs/{documentName}/swagger.json";
});
app.UseSwaggerUI(options =>
{
options.RoutePrefix = "scheduler/api-docs";
options.SwaggerEndpoint("/scheduler/api-docs/v1/swagger.json", "Scheduler API v1");
});
I am trying to configure an Nginx reverse-proxy in the container network so that I can go to, say...
http://localhost/<service-name>/api-docs
and it will redirect, inside the container network, to...
http://<service-name>:5000/<service-name>/api-docs
So, here's the Nginx configuration I've come up... basically, match the first part of the request URI, which should be the service name, and proxy to a host called the same and Nginx should add the $request_uri on automatically.
server {
listen 80;
location ~* ^/(?<target>.+)/ {
proxy_pass http://$target:5000;
proxy_redirect off;
resolver 127.0.0.11;
}
}
Here's what I get for a /scheduler/healthcheck endpoint. All good!
api-gateway_1 | 172.19.0.1 - - [27/Mar/2018:17:50:24 +0000] "GET /scheduler/healthcheck HTTP/1.1" 200 491 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36" "-"
But, when I try to go to /scheduler/api-docs, I have problems. We get to the service container and Swashbuckle does a 301 Redirect from /scheduler/api-docs to /scheduler/api-docs/.
api-gateway_1 | 172.19.0.1 - - [27/Mar/2018:17:51:18 +0000] "GET /scheduler/api-docs HTTP/1.1" 301 0 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36" "-"
And, then, things go bad... we "lose" the /scheduler part of the route!
api-gateway_1 | 172.19.0.1 - - [27/Mar/2018:17:51:18 +0000] "GET /scheduler/api-docs/ HTTP/1.1" 502 576 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36" "-"
api-gateway_1 | 2018/03/27 17:51:18 [error] 5#5: *2 connect() failed (111: Connection refused) while connecting to upstream, client: 172.19.0.1, server: , request: "GET /scheduler/api-docs/ HTTP/1.1", upstream: "http://172.19.0.5:80/api-docs:5000", host: "localhost:4000"
Why does the Swashbuckle redirect send the request back through Nginx, I thought this would all be handled by the local service, and why is Nginx stripping the necessary route prefix from this request?
How do I get this to behave?!
I tried to reconstruct the "whole" URI, just to see what happens...
- proxy_pass http://$target:5000;
+ proxy_pass http://$target:5000$request_uri;
And that got even worse!
api-gateway_1 | 172.19.0.1 - - [27/Mar/2018:18:03:48 +0000] "GET /scheduler/api-docs HTTP/1.1" 301 0 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36" "-"
api-gateway_1 | 172.19.0.1 - - [27/Mar/2018:18:03:48 +0000] "GET /scheduler/api-docs/ HTTP/1.1" 502 576 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36" "-"
api-gateway_1 | 2018/03/27 18:03:48 [error] 5#5: *2 connect() failed (111: Connection refused) while connecting to upstream, client: 172.19.0.1, server: , request: "GET /scheduler/api-docs/ HTTP/1.1", upstream: "http://172.19.0.5:80/api-docs:5000/scheduler/api-docs/", host: "localhost:4000"
FYI, everything works fine in my browser if I visit the sites directly (after publishing the ports via Docker, etc.)

Answer 1

Ahem... the problem is a "greedy" regex. The regex capture group .+, as defined, will consume everything up to the last forward-slash.
You should use a "lazy" regex capture group .+? to capture just a single URI segment between two forward-slashes, but not everything to the last forward-slash!