Change Environmet Variables at runtime (React, vite) with docker and nginx

It is not possible to dynamically inject Vite env variables. But what is possible, is to change the window object variables (assign them on runtime).
WARNNING!!! DO NOT EXPOSE ANY SENSITIVE VARIABLES THROUGH THE WINDOW OBJECT. YOUR FRONT-END APPLICATION SOURCE IS VISIBLE TO ANYONE USING IT

Steps:

1. Create your desired env files and place them in <rootDir>/public. Let's call them env.js and env-prod.js.

2. Inside your env.js and env-prod.js You want to assign your desired variables using var keyword. Also, you will have to reference these values in your source like window.MY_VAR to be able to use them.

3. Create a script tag inside your <rootDir>/index.html like this:
   <script type="text/javascript" src="./env.js"></script>.
   IMPORTANT!!! type="text/javascript" is important, because if You specify module, Vite will include your env.js source inside your minified index.js file.

4. Vite config (optional):

  plugins: [react(), tsConfigPath()],
  build: {
    emptyOutDir: true, // deletes the dist folder before building
  },
});

5. How to serve the env files on runtime. Create a node server which will serve your frontend application. But before serving the env.js file, depending on our process.env.ENVIRONMENT you can now choose which env.js to serve. Let's say my node server file is stored at <rootDir>/server/server.js:

const express = require("express");
const path = require("path");

const app = express();

const env = process.env.ENVIRONMENT || "";

console.log("ENVIRONMENT:", env);

const envFile = path.resolve("public", env ? `env-${env}.js` : "env.js");

const indexFile = path.resolve("dist", "index.html");

app.use((req, res, next) => {
  const url = req.originalUrl;
  if (url.includes("env.js")) {
    console.log("sending", envFile);
    // instead of env.js we send our desired env file
    res.sendFile(envFile);
    return;
  }
  next();
});

app.use(express.static(path.resolve("dist")));
app.get("*", (req, res) => {
  res.sendFile(indexFile);
});

app.listen(8000);

6. Serve your application build while running node ./server/sever.js command in your terminal.

7. Finally:
   my env.js contains var RUNTIME_VAR = 'test'
   my env-prod.js contains var RUNTIME_VAR = 'prod'
   After I set my process.env.ENVIRONMENT to prod. I get this file served:

My Solution is that it schould work with the links from my question. I use this approach and it works, the only thing that needs to be thought of is to use a different variable name/prefix (e.g. "APP_...") so vite doesn't change them at build time. I created a config file wich resolves the variable, for example if the app is in production than it uses the new Variable "APP_.."(which comes injected from nginx/ docker) or use "VITE_..."-variable if "APP_.." is undefined.

I came up with a solution and published it as packages to the npm registry.

With this solution, you don't need to change any code:

// src/index.js
console.log(`API base URL is: ${import.meta.env.API_BASE_URL}.`);

It separate the build step out into two build step:

During production it will be statically replaced import.meta.env with a placeholder:

// dist/index.js
console.log(
  `API base URL is: ${"__import_meta_env_placeholder__".API_BASE_URL}.`
);

You can then run the package's CLI anywhere to replace the placeholders with your environment variables:

// dist/index.js
console.log(
  `API base URL is: ${{ API_BASE_URL: "https://httpbin.org" }.API_BASE_URL}.`
);
// > API base URL is: https://httpbin.org.

Here is the documentation site: https://iendeavor.github.io/import-meta-env/.

Feel free to provide any feedback.

You can set the variables in YAML format and update them accordingly as per your requirement.

Below is the sample YAML format which we use as a template:

#Set variables once
variables:
  configuration: debug
  platform: x64

steps:

#Use them once
- task: MSBuild@1
  inputs:
    solution: solution1.sln
    configuration: $(configuration) # Use the variable
    platform: $(platform)

#Use them again
- task: MSBuild@1
  inputs:
    solution: solution2.sln
    configuration: $(configuration) # Use the variable
    platform: $(platform)

Check this SO for more insights to understand environment variables hosted in azure web app