I don’t believe the EXPOSE parameter in the Dockerfile will end up mattering to Fly ( I’m happy to be corrected).
Is it correct to assume that the PORT env var is telling the Go program what port to listen on?
What’s the connection look like in the program? It should be something like “:8080” so it listens on all network interfaces (it needs to listen on ipv6, so a connection string like “0.0.0.0:8080” won’t work).
Otherwise it will be a matter of debugging what’s going wrong, perhaps by running the container locally and seeing what network it’s bound to, etc. (making sure the PORT env var is being read, etc).