cors-anywhere deployment with Docker Compose

My ad-tracker Express app serves up queued advertisements with a client-side call to Javascript’s fetch function. This, of course, raises the issue of Cross-Origin Resource Sharing.

I use the cors-anywhere node module to allow sites with ad-tracker advertisements to access the server. Naturally, docker-compose is my preferred deployment tool.

Set up the project

Create a project directory and initialize the application with npm:

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mkdir -p sites/cors-anywhere-server && cd sites/cors-anywhere-server
npm init

Follow the npm init prompts.

Once initialized, add the cors-anywhere module to the project:

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npm install cors-anywhere --save

Copy and paste the following into index.js (or whatever entry-point you specified in the initialization step):

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// Listen on a specific host via the HOST environment variable
var host = process.env.HOST || '0.0.0.0';
// Listen on a specific port via the PORT environment variable
var port = process.env.PORT || 8080;
var cors_proxy = require('cors-anywhere');
cors_proxy.createServer({
    originWhitelist: [], // Allow all origins
    requireHeader: ['origin', 'x-requested-with'],
    removeHeaders: ['cookie', 'cookie2']
}).listen(port, host, function() {
    console.log('Running CORS Anywhere on ' + host + ':' + port);
});

This code is take verbatim from the cors-anywhere documentation.

To execute the application:

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node index.js

If it executes successfully, you should see:

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Running CORS Anywhere on 0.0.0.0:8080

Exit the app.

Docker

To create the Dockerized application image, paste the following into Dockerfile:

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FROM node
ENV NPM_CONFIG_LOGLEVEL warn
EXPOSE 8080
# App setup
USER node
ENV HOME=/home/node
  
WORKDIR $HOME
ENV PATH $HOME/app/node_modules/.bin:$PATH
ADD package.json $HOME
RUN NODE_ENV=production npm install
CMD ["node", "./index.js"]

This will build the cors-anywhere into a Docker node container.

Docker Compose

Paste the following into docker-compose.yml:

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version: '3'
services:
  node:
    build: .
    restart: always
    ports:
      - "8080"
    environment:
      - NODE_ENV=production
    volumes:
      - .:/home/node
      - /home/node/node_modules

Build the image and deploy in one step:

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docker-compose up

The last line of the console output should read:

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node_1  | Running CORS Anywhere on 0.0.0.0:8080

At this point, any request proxied through the cors-anywhere-server will be allowed access to cross-domain resources. Your client-side fetch calls can now leverage this functionality by prefixing the destination URL with the cors-anywhere-server URL. It may look something like this:

(function() {
  var CORS_SERVER = 'https://cors-server.example.com:8080';
  var AD_SERVER = 'https://ads.example.com';

  fetch(CORS_SERVER + '/' + AD_SERVER).then(function(response) {
    return response.json();    
  }).then(function(json) {     
    console.log('CORS request successful!');
    console.log(json); 
  });
})();

Done!