Hi @Johnny_Liaw ,
Can you try adding cmd = "yarn start" to the [experimental] section of fly.toml, and re-deploy to see how it goes.
Since it’ll then find the yarn.lock, the above will just be like giving yarn a kick.
Rather than removing yarn.lock, which will make it use npm for the build, etc.
Cross-referencing issues: https://community.fly.io/t/deploy-error-with-flyctl-actions-failed-to-launch-determine-start-command-failed-due-to-unhealthy-allocations/
https://fly.io/docs/reference/configuration/#the-experimental-section