Trouble Finding Port of Linked Service: Error Connection Refused

In my gitlab CI I am trying to run some Nightwatch.js tests on a nextjs app. To avoid exposing API keys to my app, I have created a microservice which proxies requests to my actual api.

The proxy service is a simple express app that listens on port 3001. Here is it’s Dockerfile which is available at registry.gitlab.com/acha5066/wedgie-travel-proxy:latest for the main CI process to use.

FROM node:12-buster

# This image will be built in CI on deploy.

COPY . /home/node/app/

WORKDIR /home/node/app/

EXPOSE 3001

CMD yarn server

Here is my .gitlab-ci.yml

image: registry.gitlab.com/acha5066/wedgie-travel/node:12-buster-1

services:
  - name: registry.gitlab.com/acha5066/wedgie-travel-proxy:latest
    alias: proxy

stages:
  - build
  - test

yarn:
  stage: build
  script:
  # Build and serve app.
  - cd $CI_PROJECT_DIR/public && yarn install
  - yarn global add grunt-cli
  - grunt build
  - cd $CI_PROJECT_DIR/public && yarn build
  artifacts:
    paths:
      - $CI_PROJECT_DIR/public/.next
      - $CI_PROJECT_DIR/public/node_modules

tests:
  stage: test
  script:
    - cd $CI_PROJECT_DIR/public && yarn start & # Starts the server in the background.
    - sleep 5 # Wait for server to start.
    - curl proxy:3001
    - cd $CI_PROJECT_DIR/public && ./node_modules/.bin/nightwatch
  artifacts:
    paths:
      - $CI_PROJECT_DIR/public/tests_output
      - $CI_PROJECT_DIR/public/geckodriver.log
      - $CI_PROJECT_DIR/public/chromedriver.log
    when: always

As you can see, I’m trying to simply curl the service alias and the port (curl proxy:3001) but I am continually getting connection refused. So how do I find the port to use for my service. If I expose port 3001 in the Dockerfile should it not be available there from curl.

Help appreciated as I’m stuck