Docker Nginx: host not found in upstream

I have my docker app running in the aws EC2 instance, and I am currently trying to map the app to the external IP address using Nginx. Here is a snap shot of the containers that I have running:

My test-app is a fairly simple app that displays a static html website. And I deployed it using the following command:

docker run -d --name=test-app test-app

The nginx-proxy has the following proxy.conf

server {
  listen 80;
  location / {
    proxy_pass http://test-app;
  }
}

Here is the Dockerfile for the nginx proxy:

FROM nginx:alpine

RUN rm /etc/nginx/conf.d/*

COPY proxy.conf /etc/nginx/conf.d/

nginx-proxy is run using the following command: docker run -d -p 80:80 --name=nginx-proxy nginx-proxy

However, the nginx container never runs, and here the error log I get

2020/03/27 15:55:19 [emerg] 1#1: host not found in upstream "test-app" in /etc/nginx/conf.d/proxy.conf:5
nginx: [emerg] host not found in upstream "test-app" in /etc/nginx/conf.d/proxy.conf:5