OK that worked. Thanks. It seems to take quite a while for the app to come back up after a process exit so while the first request completes in 100ms, a second, fired at the same time as the first, takes ~14sec to complete. Watching the logs it looks like the VM is up and running but waits quite a while for the health checks. I dropped down the numbers in services.tcp_checks but it didn’t get much better.
I saw mention of max-per-region in the TOML doc so added the following. It seemed to help two concurrent requests the first time but there after it was about 20sec cycle time.
[deploy]
max-per-region = 2
Rather than chase this down, I’d happily move to Machines if I could get an example of a Node based machine that is built by the Fly build setup and can receive requests (see Tease us with more “machine” info? - General - Fly.io. It feels soooo close.