VueCLI3 app (nginx/docker) use environment specific variables

I think I've accomplished to overcome this case. I am leaving the resolution here.

1. Define your environment-specific environment variables in .env.development (for development purposes) and add them also to the Pod configuration with correxponding values.

2. Add a configuration.js file somewhere in your Vue project source folder. It would act as a wrapper for determining whether the runtime is development (local) or production (container). It is like the one shown here, but importing/configuring dotenv is not required:

   export default class Configuration {
     static get EnvConfig () {
       return {
         envKey1: '$ENV_KEY_1',
         envKey2: '$ENV_KEY_2'
       }
     }
   
     static value (key) {
       // If the key does not exist in the EnvConfig object of the class, return null
       if (!this.EnvConfig.hasOwnProperty(key)) {
         console.error(`Configuration: There is no key named "${key}". Please add it in Configuration class.`)
         return
       }
   
       // Get the value
       const value = this.EnvConfig[key]
   
       // If the value is null, return
       if (!value) {
         console.error(`Configuration: Value for "${key}" is not defined`)
         return
       }
   
       if (!value.startsWith('$VUE_APP_')) {
         // value was already replaced, it seems we are in production (containerized).
         return value
       }
   
       // value was not replaced, it seems we are in development.
       const envName = value.substr(1) // Remove $ and get current value from process.env
       const envValue = process.env[envName]
   
       if (!envValue) {
         console.error(`Configuration: Environment variable "${envName}" is not defined`)
         return
       }
   
       return envValue
     }
   }
   
   

3. Create an entrypoint.sh. With some modification, it would look like follows:

   #!/bin/bash
   
   function join_by { local IFS="$1"; shift; echo "$*"; }
   
   # Find vue env vars
   vars=$(env | grep VUE_APP_ | awk -F = '{print "$"$1}')
   vars=$(join_by ',' $vars)
   echo "Found variables $vars"
   
   for file in /app/js/app.*;
   do
     echo "Processing $file ...";
   
     # Use the existing JS file as template
     cp $file $file.tmpl
     envsubst "$vars" < $file.tmpl > $file
     rm $file.tmpl
   done
   
   nginx -g 'daemon off;'
   

4. In your Dockerfile, add a CMD for running this entrypoint.sh script above as a bootstrapping script during container creation. So that, every time you start a container, it will get the environment variables from the pod configuration and inject it to the Configuration class shown in Step 2.

   # build stage
   FROM node:lts-alpine as build-stage
   
   # make the 'app' folder the current working directory
   WORKDIR /app
   
   # Copy package*.json and install dependencies in a separaate step to enable caching
   COPY package*.json ./
   RUN npm install
   
   # copy project files and folders to the current working directory
   COPY ./ .
   
   # install dependencies and build app for production with minification
   RUN npm run build
   
   # Production stage
   FROM nginx as production-stage
   
   RUN mkdir /app
   
   # copy 'dist' content from the previous stage i.e. build
   COPY --from=build-stage /app/dist /app
   
   # copy nginx configuration
   COPY nginx.conf /etc/nginx/nginx.conf
   
   # Copy the bootstrapping script to inject environment-specific values and pass it as argument current to entrypoint
   COPY entrypoint.sh entrypoint.sh
   
   # Make the file executable
   RUN chmod +x ./entrypoint.sh
   
   CMD ["./entrypoint.sh"]
   
   

Finally, instead of process.env use our wrapper configuration class like Configuration.value('envKey1'). And voila!