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Deploy an Express.js App to Fly.io

Deploy an Express.js app with an encrypted .env.vault file to Fly.io.

Find a complete code example on GitHub for this guide.

Initial setup

Install express.

npm install express --save

Create an index.js file with the web server code.

index.js

const PORT = process.env.PORT || 3000
const express = require('express')
const app = express()

app.listen(PORT, () => {
  console.log(`Running on port ${PORT}.`)
})

app.get('/', function (req, res) {
  res.send(`Hello ${process.env.HELLO}`)
})

Add a start script to the package.json file.

package.json

{
  "scripts": {
    "start": "node index.js"
  }
}

Commit that to code and deploy it to Fly.

brew install flyctl
flyctl launch
flyctl deploy --remote-only --no-cache

Once deployed, your app will say Hello undefined as it doesn't have a way to access the environment variable yet. Let's do that next.

yourapp.fly.dev

Fly.io bug: While writing this guide we ran into the error "failed to fetch an image or build from source: error building: ... node:20.4.0-slim: docker.io/library/node:20.4.0-slim: not found". If you also experience this set NODE_VERSION=18.16.1 in your Dockerfile and redeploy.

Install dotenv

Install dotenv.

npm install dotenv --save # Requires dotenv >= 16.1.0

Create a .env file in the root of your project.

.env

# .env
HELLO="World"

As early as possible in your application, import and configure dotenv.

index.js

require('dotenv').config()
console.log(process.env) // remove this after you've confirmed it is working

const PORT = process.env.PORT || 3000
const express = require('express')
...

Try running it locally.

node index.js
{
  ...
  HELLO: 'World'
}
Server running on port:3000/

It should say Hello World.

Great! process.env now has the keys and values you defined in your .env file. That covers local development. Let's solve for production next.

Build .env.vault

Push your latest .env file changes and edit your production secrets. Learn more about syncing

npx dotenv-vault@latest push
npx dotenv-vault@latest open production

Use the UI to configure those secrets per environment.

www.dotenv.org

Then build your encrypted .env.vault file.

npx dotenv-vault@latest build

Its contents should look something like this.

.env.vault

#/-------------------.env.vault---------------------/
#/         cloud-agnostic vaulting standard         /
#/   [how it works](https://dotenv.org/env-vault)   /
#/--------------------------------------------------/

# development
DOTENV_VAULT_DEVELOPMENT="/HqNgQWsf6Oh6XB9pI/CGkdgCe6d4/vWZHgP50RRoDTzkzPQk/xOaQs="
DOTENV_VAULT_DEVELOPMENT_VERSION=2

# production
DOTENV_VAULT_PRODUCTION="x26PuIKQ/xZ5eKrYomKngM+dO/9v1vxhwslE/zjHdg3l+H6q6PheB5GVDVIbZg=="
DOTENV_VAULT_PRODUCTION_VERSION=2

Set DOTENV_KEY

Fetch your production DOTENV_KEY.

npx dotenv-vault@latest keys production
# outputs: dotenv://:[email protected]/vault/.env.vault?environment=production

Set DOTENV_KEY on Fly.io.

flyctl secrets set NODE_ENV=production DOTENV_KEY='dotenv://:[email protected]/vault/.env.vault?environment=production'

Deploy

Commit those changes safely to code and deploy again.

flyctl deploy --remote-only --no-cache

That's it! On deploy, your .env.vault file will be decrypted and its production secrets injected as environment variables – just-in-time.

yourapp.fly.dev

You'll know things worked correctly when you see 'Loading env from encrypted .env.vault' in your logs. If a DOTENV_KEY is not set (for example when developing on your local machine) it will fall back to standard dotenv functionality.

flyctl logs

You succesfully used the new .env.vault standard to encrypt and deploy your secrets. This is much safer than scattering your secrets across multiple third-party platforms and tools. Whenever you need to add or change a secret, just rebuild your .env.vault file and redeploy.