Pass environment variable into a Vue App at runtime

Create a file config.js with your desired configuration. We will use that later to create a config map that we deploy to Kubernetes. Put it into your your Vue.js project where your other JavaScript files are. Although we will exclude it later from minification, it is useful to have it there so that IDE tooling works with it.

const config = (() => {
  return {
    "VUE_APP_ENV_MyURL": "...",
  };
})();

Now make sure that your script is excluded from minification. To do that, create a file vue.config.js with the following content that preserves our config file.

const path = require("path");
module.exports = {
  publicPath: '/',
  configureWebpack: {
    module: {
      rules: [
        {
          test: /config.*config\.js$/,
          use: [
            {
              loader: 'file-loader',
              options: {
                name: 'config.js'
              },
            }
          ]
        }
      ]
    }
  }
}

In your index.html, add a script block to load the config file manually. Note that the config file won't be there as we just excluded it. Later, we will mount it from a ConfigMap into our container. In this example, we assume that we will mount it into the same directory as our HTML document.

<script src="<%= BASE_URL %>config.js"></script>

Change your code to use our runtime config:

this.displayURL = config.VUE_APP_ENV_MyURL || process.env.VUE_APP_ENV_MyURL 

In Kubernetes, create a config map that uses the content your config file. Of course, you wanna read the content from your config file.

apiVersion: v1
kind: ConfigMap
metadata:
  ...
data:
  config.js: |
    var config = (() => {
      return {
        "VUE_APP_ENV_MyURL": "...",
      };
    })();

Reference the config map in your deployment. This mounts the config map as a file into your container. The mountPath Already contains our minified index.html. We mount the config file that we referenced before.

apiVersion: apps/v1
kind: Deployment
metadata:
  ...
spec:
  ...
  template:
    ...
    spec:
      volumes:
        - name: config-volume
          configMap:
            name: ...
      containers:
        - ...
          volumeMounts:
                - name: config-volume
                  mountPath: /usr/share/nginx/html/config.js
                  subPath: config.js

Now you can access the config file at <Base URL>/config.js and you should see the exact content that you put into the ConfigMap entry. Your HTML document loads that config map as it loads the rest of your minified Vue.js code. Voila!

I am adding my working solution here, for those who are still having trouble. I do think that @Hendrik M Halkow 's answer is more elegant, though I couldn't manage to solve it using that, simply just because of my lack of expertise in webpack and Vue.I just couldn't figure out where to put the config file and how to refer it.

My approach is to make use of the environment variables with constants (dummy values) to build it for production, then replace that constants in the image using a custom entrypoint script. The solution goes like this.

I have encapsulated all configs into one file called app.config.js

export const clientId = process.env.VUE_APP_CLIENT_ID
export const baseURL = process.env.VUE_APP_API_BASE_URL

export default {
  clientId,
  baseURL,
}

This is used in the project just by looking up the value from config file.

import { baseURL } from '@/app.config';

Then I am using standard .env.[profile] files to set environment variables. e.g. the .env.development

VUE_APP_API_BASE_URL=http://localhost:8085/radar-upload
VUE_APP_CLIENT_ID=test-client

Then for production I set string constants as values. e.g. the .env.production

VUE_APP_API_BASE_URL=VUE_APP_API_BASE_URL
VUE_APP_CLIENT_ID=VUE_APP_CLIENT_ID

Please not here the value can be any unique string. Just to keep the readability easier, I am just replacing the environment variable name as the value. This will just get compiled and bundled similar to development mode.

In my Dockerfile, I add an entrypoint that can read those constants and replace it will environment variable values.

My Dockerfile looks like this (this is pretty standard)

FROM node:10.16.3-alpine as builder

RUN mkdir /app
WORKDIR /app

COPY package*.json /app/
RUN npm install

COPY . /app/

RUN npm run build --prod

FROM nginx:1.17.3-alpine

# add init script
COPY ./docker/nginx.conf /etc/nginx/nginx.conf

WORKDIR /usr/share/nginx/html

COPY --from=builder /app/dist/ .

COPY ./docker/entrypoint.sh /entrypoint.sh

# expose internal port:80 and run init.sh
EXPOSE 80

ENTRYPOINT ["/entrypoint.sh"]
CMD ["nginx", "-g", "daemon off;"]

Then create a ./docker/entrypoint.sh file as below.

#!/bin/sh

ROOT_DIR=/usr/share/nginx/html

# Replace env vars in JavaScript files
echo "Replacing env constants in JS"
for file in $ROOT_DIR/js/app.*.js* $ROOT_DIR/index.html $ROOT_DIR/precache-manifest*.js;
do
  echo "Processing $file ...";

  sed -i 's|VUE_APP_API_BASE_URL|'${VUE_APP_API_BASE_URL}'|g' $file 
  sed -i 's|VUE_APP_CLIENT_ID|'${VUE_APP_CLIENT_ID}'|g' $file

done

echo "Starting Nginx"
nginx -g 'daemon off;'

This enables me to have runtime configurable image that I can run on many environments. I know it is a bit of a hack. But have seen many people do it this way.

Hope this helps someone.