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April 24, 2025

How to work with Multiple ENV files in Serverless Framework??

env

nodejs

serverless

Contents

Preface

We can hard-code those env values into serverless.yml, but of course it is not ideal.

If we have already separated variables into default-one and stage-specific ones, we definitely want to reuse them.

Requirements

  • A plugin serverless-dotenv-plugin is required to load multiple env files and;

  • We need to write custom parser when our env file is a json file (more readable than an ordinary .env file, especially when there is a long array).

Deployment Configuration

The serverless.yml

Here the order of variables in path does matter, varibles in .env.dev.json can override those in .env.json:

plugins:
  - serverless-dotenv-plugin
......
custom:
  dotenv:
    path:
      - .env.json
      - .env.dev.json
    dotenvParser: "./jsonParser.js"

The parameter dotenvParser is optional, as long as our .env files are simply key=value's, otherwise we need a parser to process non-ordinary values (like an array).

jsonParser.js
1const fs = require("fs");
2
3module.exports = function ({ paths }) {
4  const envVarsArray = paths.map((path) => {
5    try {
6      const fileContent = fs.readFileSync(path, "utf8");
7      const jsonData = JSON.parse(fileContent);
8
9      const stringifiedData = {};
10      for (const key in jsonData) {
11        const value = jsonData[key];
12        const ordinaryENVType = ["string", "boolean", "number"];
13
14        if (ordinaryENVType.includes(typeof value)) {
15          stringifiedData[key] = jsonData[key];
16        } else if (Array.isArray(jsonData[key])) {
17          stringifiedData[key] = jsonData[key].map((v) => String(v)).join(",");
18        } else {
19          //ignore
20        }
21      }
22
23      return stringifiedData;
24    } catch (error) {
25      console.error(`Error reading/parsing ${path}:`, error.message);
26      return {};
27    }
28  });
29
30  return envVarsArray.reduce((acc, curr) => ({ ...acc, ...curr }), {});
31};

Special treatments have been made from line 14-18, any list is transformed into ,-concated string (remember to split by , in the program).