Just to help others:
I spent few moments trying to find out how to run VictoriaMetrics on Fly.io.
I got that running, but it did not respond on http://hostname.internal:8428
Locally works ok.
So, problem is that VictoriaMetrics does not have IPv6 enabled by default (this was surprise for me) and it needs to be enabled via command line parameter.
app = "test-victoriametrics" primary_region = "arn" [mount] destination = "/victoria-metrics-data" source = "victoriametrics_data"
FROM victoriametrics/victoria-metrics ENTRYPOINT ["/victoria-metrics-prod", "-enableTCP6"]