region specific flycast/private ipv6

I tried creating a private ipv6 for a spesific region using:
fly ips allocate-v6 --region fra --private
But when I list it using fly ips list, it’s created as a global ip.
Is this combination not supported?

It would be nice to get support for <region>.<name>.flycast, in the same way it works for .internal.

Hey @anders1

Is this combination not supported?


Could you tell more about your use case, please? What are you trying to achieve by having regional flycast addresses?

I got apps in different networks, so I can’t use internal addresses, but I still want to make sure I can reach the app that is in the other network on the same region.

It can look something like the followin. So I still want to load balance between the vm’s in one region:
network 1
app A

  • vm fra
  • vm fra
  • vm den

network 2
app B

  • vm fra
  • vm fra
  • vm den


Regional IPs don’t really guarantee this. They only guarantee that the request is gonna be accepted to Fly network by an edge server running in this region. Whether or not the request is gonna be routed to a machine running in the same region depends on multiple factors:

  • are there healthy instances in the region
  • are there instances below hard limit
  • is network connectivity between edge and worker hosts fine

Flycast addresses are the same, but the difference is that the worker host where the client is running acts like an edge.

I think the closest we have right now to do something like this is fly-prefer-region request header: Dynamic Request Routing · Fly Docs

1 Like

Thanks for the response.
This is TCP only, so fly-prefer-region will not work.
The hard and soft limits are set very high, but based on latency it seems to not hit the correct region.
I will do some experiments and see if I can figure it out.

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