Why am I getting "ERR_CONNECTION_REFUSED" when querying by sidecar-hosted backend in Azure App Service?

------------Update------------

In the end I never solved this problem, and instead deployed the api as its own app service which solved the problem.

----------- Original Post -------------------

I'm trying to deploy a fairly basic web app in Azure App Service. I have a backend image (running django+graphql) and and a frontend image (running vue+apollo), and when I run them locally either separately or via docker-compose it works with no issues.

Once I deploy the app in Azure App Service, with the frontend as the main container, and the backend as the sidecar, I get "ERR_CONNECTION_REFUSED" when Apollo queries the graphql api in the backend.

Apollo-config

import {
    ApolloClient,
    InMemoryCache,
} from "@apollo/client/core";
import { createApolloProvider } from "@vue/apollo-option";
import createUploadLink from "apollo-upload-client/createUploadLink.mjs";

const httpLink = createUploadLink({
  uri: "http://localhost:8080/graphql",
});

// Cache implementation
const cache = new InMemoryCache();

// Create the apollo client
export const apolloClient = new ApolloClient({
  link: httpLink,
  cache,
});

export const ApolloProvider = createApolloProvider({
  defaultClient: apolloClient,
});

Docker compose

services:
  backend:
    container_name: backend
    build: 
      context: ./backend
    ports:
      - "8080:8080"
  frontend:
    container_name: vue_frontend
    build:
      context: ./vue
    ports:
      - "80:80"

Frontend dockerfile

FROM node:22.14-alpine

RUN npm install -g http-server 

WORKDIR /vue

COPY package*.json ./
COPY .npmrc .npmrc

RUN --mount=type=secret,id=npmrc,target=.npmrc npm install

COPY . .

EXPOSE 80 8080

CMD ["npm", "run", "dev", "--", "--port", "80", "--host"]

Backend dockerfile

FROM python:3.10-slim

RUN mkdir /backend 

WORKDIR /backend

ENV PYTHONDONTWRITEBYTECODE=1
ENV PYTHONUNBUFFERED = 1

RUN pip install --upgrade pip --trusted-host pypi.org

COPY requirements.txt /backend/

RUN apt-get update && \
    apt-get install -y libpq-dev gcc

RUN pip install --no-cache-dir -r requirements.txt --trusted-host pypi.org

COPY . /backend/

EXPOSE 8080 80

CMD ["daphne", "-b", "0.0.0.0", "-p", "8080", "backend.asgi:application"]

The only thing that has "worked" so far is running the backend locally, and then the app will receive data. This suggest that I am actually querying a website with the apollo code as opposed to anything on the network host.

From the docs: localhost:<port> should be sufficient

MS-sidecar-tutorial

I have tried giving different addresses in the uri in the apollo-config, but if I try "localhost:8000" instead I just get the error that localhost schema is not supported.

And if I try "<app-url>/graphql" I just get a 404