Issue with nginx reverse proxy to FastAPI container in Azure Container Apps

Question

Issue with nginx reverse proxy to FastAPI container in Azure Container Apps

Joris 10

Hi,

I'm trying to setup an nginx reverse proxy on Container Apps. I have the nginx container and a FastAPI container in a Container App Environment with simple virtual network + subnet + private DNS zone. The API's ingress is set to internal, and the nginx ingress to external.

When I go to the nginx URL I get:

"Error 404 - This Container App is stopped or does not exist."

Though I'm able to verify that I can reach the nginx container's by making it serve a local html file on /nginx. (see config below)

When I attach to the nginx Container App on Azure, I am able to curl the API at http://api-container:80 and get the expected response.

This makes me think there's an (Azure-specific?) problem with the nginx configuration, since it does work locally with Docker Compose.

Some advice would be much appreciated! I can post my nginx config but it appears I can't post it in this question because it becomes too long.

Joris 10

events {}
http {
	upstream chat_api_group {
		server chat-api:80
	}
	server {
		listen 80;
		location / {
			proxy_pass http://chat_ui_group/;
			proxy_set_header Host $host
			proxy_set_header X-Real-IP $remote_addr
			proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for
			proxy_set_header X-Forwarded-Proto $scheme
			proxy_http_version 1.1
		}
		location /nginx {
			alias /usr/share/nginx/html/;
			index index.html;
		}

	}
}

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Joris 10 Reputation points

2024-11-01T11:10:40.4233333+00:00

events {} http { upstream chat_api_group { server chat-api:80 } server { listen 80; location / { proxy_pass http://chat_ui_group/; proxy_set_header Host $host proxy_set_header X-Real-IP $remote_addr proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for proxy_set_header X-Forwarded-Proto $scheme proxy_http_version 1.1 } location /nginx { alias /usr/share/nginx/html/; index index.html; } } }

Answer 1

had to manually set the Host header to the hostname (the container name in my case):

proxy_set_header Host chat-ui;  # Set Host header explicitly to chat-ui

When I ran a nslookup <api-container-name> from within the nginx container, I noticed that curl <resolved-ip-address> gave a 404, while a curl <api-container-name> got me a 200.

I don't entirely understand what's going on, but it seems Azure's internal routing system uses the Host header to find the right service, and the internal IP of that service is not meant to be used directly. I guess nginx sets the Host header to itself rather than the container it's forwarding to.

If anyone has a better explanation, let me know!

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Issue with nginx reverse proxy to FastAPI container in Azure Container Apps

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