It takes getting used to, that’s for sure.
allocation error is a generic error. It must contain other nested error text within it (ex: A, B). Can you please share the complete error text you’re seeing?
A guess: The error may be due to app’s squid process not listening on ports Fly might be expecting it to (Fly doesn’t honour the EXPOSE directive in the dockerfile, the equivalent of it is declaring port in [[services]] section of an app’s fly.toml configuration) [0].
[0] Fly doesn’t run docker / runc images as-is; it transmorgifies it to run it in a Firecracker VM, and so, the way it currently is, is that a part of the configuration must live in a fly.toml horcrux.