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Illustration by Annie Ruygt of apps resting on clouds, all connected by pathways Flycast provides network addressing and routing for private apps on Fly.io private networks. With Flycast, requests to your private apps get routed through the Fly Proxy, rather than Machine-to-Machine via default private networking. And unlike private networking using .internal addresses you don’t need to keep Machines running for the app to be reachable. Use Flycast within your organization’s private network to:
  • Have Fly Proxy autostop/autostart Machines based on network requests.
  • Get Fly Proxy’s geographically aware load balancing for private services.
  • Connect to a service from another app that can’t use DNS.
  • Connect from third-party software, like a database, that doesn’t support round-robin DNS entries.
  • Access specific ports or services in your app from other Fly.io organizations.
  • Use advanced Fly Proxy features like TLS termination or PROXY protocol support.

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Flycast quickstart

The fastest way to create a new private app with a Flycast address:
Access the services on the Flycast private IPv6 address, or with my-app-name.flycast, from other apps in the organization’s default private network.

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Flycast requirements

To use Flycast for your app, you need:
  • A Flycast private IPv6 address for your app on one of your Fly.io organization networks.
  • Your app to bind to 0.0.0.0:port. (Binding to fly-local-6pn:<port> won’t work for Flycast.)
  • Services configured in your app’s fly.toml with an [http_service] or [services] section. Don’t use force_https; Flycast is HTTP-only.
Warning: If you have public IP addresses assigned to your app, then services in fly.toml are exposed to the public internet. Verify your app’s IP addresses with fly ips list, and remove public IP addresses as needed with: fly ips release [ip address] [ip address] ....

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Allocate a Flycast address

A Flycast address is an app-wide private IPv6 address that Fly Proxy can route to over the private network. By default, the Flycast IP address is allocated on an app’s default organization network. There are a few ways to add a Flycast address to an existing app. Allocate a Flycast address on deploy:
Allocate a Flycast address without deploying:

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Access an app from another organization

You can use Flycast to expose an app in one Fly.io organization to another Fly.io organization; the app won’t be accessible via Flycast from its own organization. Use the --org option when you allocate the Flycast address:

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Access an app from another private network

You can also use Flycast to expose an app on one private network to another private network in your organization; the app won’t be accessible via Flycast from its own network. Use the --network option to specify the network from which requests will originate:
Learn more about custom private networks.

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Flycast and Fly.io DNS

Flycast addresses can also be found by using the Fly.io DNS. If an app has a Flycast address allocated to it, there will be an AAAA record at my-app-name.flycast.

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More Flycast