Next.js does support environment variables, but only at build time. This means you must rebuild your app for each target environment, which violates the Build once, deploy many principle.
These examples contain everything needed to get a Next.js production environment up and running with Docker Compose and being able to read environment variables from the environment section in your docker-compose.yml file when the container starts.
Both examples read the system variables and generate a public __env.js/__ENV.js file which exposes the NEXT_PUBLIC_ variables to the client.
- with-env.sh uses a bash script.
- with-next-runtime-env uses Next Runtime Environment package.