This was a really great guide thank you! I also had to cross-reference the asset management guide:
https://github.com/phoenixframework/phoenix/blob/master/guides/asset_management.md
That I found after this forum post on external flags for esbuild. You’ll notice that the asset_management guide is updated to reflect external: rather than external=. I also cross-referenced with PragProg’s free guide on Tailwind with esbuild, particularly they add slightly to the deploy script in the assets/package.json:
"scripts": {
"deploy": "NODE_ENV=production tailwindcss --postcss --minify --input=css/app.css --output=../priv/static/assets/app.css"
},
Finally, I had to make slight adjustments because Metamorphic has an umbrella app structure. So, my base project mix.exs has this:
"assets.deploy": [
"cmd --cd ../metamorphic_web/assets npm run deploy",
"esbuild default --minify",
"phx.digest"
]
And my esbuild config expands the path as such:
cd: Path.expand("../apps/metamorphic_web/assets", __DIR__)
That did the trick for me along with making sure my asset handling with priv/static was updated for deployment following the upgrade from a 1.5 app to 1.6.
So, if anyone else is working in an umbrella app, then hopefully this helps you out too. And, again, thank you for the wonderful guide. 
