How to configure DNS using Heroku and Google Domains

May 25, 2019

My app is composed of two Docker images, the first one is a JavaScript SPA and second one is the server which is a Node.js API. The client basically call the API through HTTP. Here is the Dockerfile for the client.

FROM node:10 AS builder 
WORKDIR /codamit-client
COPY package.json 
./RUN npm install
COPY ./.env.production ./.env
COPY . .
RUN npm run build

FROM nginx:1.17.0
COPY nginx/default.conf.template /etc/nginx/conf.d/default.conf.template
COPY nginx/nginx.conf /etc/nginx/nginx.conf
COPY --from=builder /codamit-client/dist /usr/share/nginx/html
CMD /bin/bash -c "envsubst '\$PORT' < /etc/nginx/conf.d/default.conf.template > /etc/nginx/conf.d/default.conf" && nginx -g 'daemon off;'

And here is the Dockerfile for the server.Note that for environmental variables I’m using a .env file dropped inside the container at build time.

When I run the container the CMD uses dotenv which basically map values from the .env file to the Node.js process.

FROM node:10
WORKDIR /usr/src/codamit-server
COPY package.json ./
RUN npm install
COPY ./.env.production ./.env
COPY . .
RUN npm run build
CMD [ "node", "-r", "dotenv/config", "dist/index.js" ]

Next to that Heroku provide a CLI to manage Docker images. I wrote a small npm script to build, push and release images in one single command.

Custom domains

At this point I had two services running online under Heroku defaults domains.

  • The client hosted on
  • The API hosted on

I wanted to be able to visit the app under and the API to respond under, let’s see how.

1- Add Heroku custom domains

Firstly I created custom domains for each project using Heroku dashboard.

Project settings > Domains and certificates > Add Domain

I added for the client and for the API. It gives me two DNS addresses that I reused later in Google Domains interface. Last but not least I configured the SSL to automatically generates certificates, it requires to upgrade the Dyno to the paying plan.

2- Configure Google Domains DNS settings

In the DNS section > Synthetic records panel I added :

Sub-domain : @
Temporary redirection (302) : ✅
Forward path : ✅
Destination URL :
Activate SSL : ✅

Then in the Custom Resources Records panel I created two records :

Name : www
Type : CNAME
TTL : 1h
Data : * paste Heroku DNS target *Name : www.api
Type : CNAME
TTL : 1h
Data : * paste Heroku DNS target *

I needed to wait a short time due to DNS propagation. To ensure DNS are well configured we can run :

$ host

It should return that is an alias for the Heroku DNS target I pasted just before from the Heroku dashboard. is an alias for [* DNS target *][* DNS target *] has address [* IP *]

I'm Edouard Bozon, I play almost everyday with web technologies. I focus my work on JavaScript, mainly around Angular and Node.js. I'm self employed, always open to new opportunities, so let's keep in touch.