Deploy on GitHub push questions

Questions / Help
1

I’m exploring the GitHub / Fly.io integration and Launch UI to figure out whether auto-deploy on push to GitHub is right for me.

My fly org has two apps, designated staging and production.
Both apps share a single Github repo and a single fly.toml file.
The shared fly.toml file omits the app key, and instead expects the --app argument to be provided at deploy time, indicating the target for the deployment:

fly deploy --app staging     # deploy to staging
fly deploy --app production  # deploy to production

Question 1

From the Launch UI, when I connect the staging app to the GitHub repo (that has an existing fly.toml file with no app key), does it infer the app based on which Fly app it is connected to?

Or is it mandatory for the app key to be specified in fly.toml when using the GitHub integration?

Question 2

When deploying with the CLI, my Dockerfile expects a --build-arg that indicates the base image version to use:

fly deploy --build-arg NODE_VERSION=X.y.z

# Dockerfile

ARG NODE_VERSION

FROM node:${NODE_VERSION}-alpine

The intention here is to replicate something similar to how Heroku’s nodejs buildpack works (which auto-detects the version of node to use from the engines.node property in package.json).

For reference, here’s what a Heroku build log looks like, showing it detecting the node/npm versions to use:

-----> Building on the Heroku-24 stack
-----> Deleting 15 files matching .slugignore patterns.
-----> Using buildpack: heroku/nodejs
-----> Node.js app detected
       
-----> Installing binaries
       engines.node (package.json):   22.11.0
       engines.npm (package.json):    10.9.1
       
       Resolving node version 22.11.0...
       Downloading and installing node 22.11.0...
       Bootstrapping npm 10.9.1 (replacing 10.9.0)...
       npm 10.9.1 installed

My deploy commands are defined as npm scripts that read the engines.node version and pass it as a --build-arg:

{
  "scripts": {
    "deploy": "fly deploy --build-arg NODE_VERSION=$npm_package_engines_node",
    "deploy:staging": "npm run deploy -- --app staging",
    "deploy:production": "npm run deploy -- --app production"
  },
  "engines": {
    "node": "22.11.0"
  }
}

Of course, I could simply specify this in fly.toml:

[build.args]
  NODE_VERSION="22.11.0"

…but I’m trying to avoid having multiple places that need to be updated when the version of Node changes, and I like the idea of engines.node being the canonical place to store this.

With all that said, does this suggest that auto-deploy on push to GitHub is unlikely to work in my scenario given that I’m providing both --app and --build-arg at deploy time?

Question 3

When linking the staging app and GitHub repo through the Launch UI, it creates a production environment in GitHub that deploys go to.

Can the GitHub environment name be changed to staging, or does the Fly.io integration specifically need an environment named production?