Public Network Services

Fly.io has public and private network services available. The public network services connect apps to the wider public internet, while the private network services allow apps to communicate with other apps within the Fly.io private network.

Anycast IP addresses

IPv6 addresses and shared IPv4 Anycast addresses are free. Dedicated IPv4 addresses are billed monthly.

About Anycast

We announce global IP blocks from all of our datacenters over BGP, otherwise known as Anycast. Anycast is a core internet routing mechanism that connects clients to the “nearest” server advertising a block of IPs. You can read all about it on Wikipedia.

IPv6

A new Fly App running a public service configured in fly.toml automatically gets a dedicated Anycast IPv6 address when it’s first deployed.

Shared IPv4

Along with the dedicated IPv6 address, apps are automatically given a shared Anycast IPv4 address on the first deployment when they’re configured to handle one or both of the following protocols and ports in fly.toml:

• HTTP on port 80, or
• TLS & HTTP on port 443

This includes apps configured with the simplified [http_service] section, which handles only these protocols and ports by default.

You can use a shared IPv4 address for TCP ports other than 80 and 443 by using the TLS handler when you specify the port.

Shared IPv4 addresses are recommended unless you have an explicit need for your own IP. Shared IPv4 addresses are shared across many apps and organizations. Routing is based on your app’s domain.

To allocate a shared IPv4 to an app without a public IPv4 address, run:

fly ips allocate-v4 --shared

Dedicated IPv4

Dedicated IPv4 addresses are billed monthly.

Shared IPv4 addresses are recommended unless you have an explicit need for your own IP. Some of the reasons to use a dedicated IPv4 address include:

• Your app uses a non-HTTP protocol that doesn’t use TLS.
• Your app needs to do something over UDP (we don’t support UDP over shared IPv4 or dedicated IPv6).
• You want your app to accept raw TCP and handle TLS termination.
• You have a Fly Postgres exposed to the internet over TLS for external connections.

Allocating a dedicated IPv4 Anycast address is opt-in only. To manually allocate a dedicated IPv4 address for your app, run:

fly ips allocate-v4

After allocating a dedicated IPv4 address, release the shared IPv4 address:

fly ips release <ip address to release>

Switch from dedicated IPv4 to shared IPv4

The following steps should allow you to switch an app with a custom domain from a dedicated IPv4 address to a free shared IPv4 without downtime.

1. Add a shared IPv4 address with flyctl ips allocate-v4 --shared.
2. If you don’t use a CNAME to .fly.dev, add the shared IPv4 as an A record.
3. Confirm your app works via shared IP: curl -Iv http://<your-hostname> --resolve <your-hostname>:80:<new-shared-ipv4>. You should receive a 301 redirect response.
4. If you are using a custom domain and don’t already have an SSL certificate for this app, create one. The cert is required for routing to your app via the custom domain, even for HTTP connections.
5. Wait for DNS caches to clear. Five minutes is likely enough, but this varies wildly. This is determined by the larger of your DNS record’s TTL and that of our <your-app>.fly.dev record.
6. Remove the dedicated IPv4 from the app using fly ips release <ipv4-address-to-release>. You can view your app’s IP addresses using fly ips list.
7. Remove the unwanted IPv4 address from your DNS if it was set manually as an A record.

If you do not have a custom domain (your app is accessed by its .fly.dev address), you don’t have to change any DNS records yourself, and you don’t need to add your own SSL cert.

Connection handlers

Handlers convert TCP connections into something your app can handle. Use handlers to specify which middleware applies to incoming TCP connections for each port you accept external connections on.

TCP pass through

If you don’t specify handlers, we just forward TCP to your app as-is. This is useful if you want to handle TLS termination yourself, for example.

Configure connection handlers

Set the handlers config setting in the services.ports section of your fly.toml file.

Valid handler strings:

• "http": Convert TCP connection to HTTP
• "tls": Convert TLS connection to unencrypted TCP
• "pg_tls": Handle TLS for PostgreSQL connections
• "proxy_proto": Wrap TCP connection in PROXY protocol

You can also configure TLS options for the [http_service] section, which has a TLS (and HTTP) handler by default on port 443.

HTTP handler

Many apps have limited HTTP support, the http handler normalizes HTTP connections and sends HTTP 1.1 requests to the application process. This is roughly how nginx and other reverse proxies work, and allows your app to globally accept modern HTTP protocols (like HTTP/2) without extra complexity.

If your application stack has good HTTP/2 support (like Go), you will get better performance accepting TCP connections directly, and using the TLS handler to terminate SSL. Your app does need to understand h2c for this to work, however.

The HTTP handler adds a number of standard HTTP headers to requests, and a few Fly.io-specific headers for convenience:

You can set a preference on HTTP requests for which region you would like to connect to. You can specify a single region or multiple regions in order of preference:

Fly-Prefer-Region: iad

Or with multiple preferences (tries regions in order):

Fly-Prefer-Region: iad,ord,us,na

You can set a preference for a specific machine instance:

Fly-Prefer-Instance-Id: instance-number

You can force routing to a specific machine instance:

Fly-Force-Instance-Id: instance-number

Configuration example in fly.toml:

[[services]]
...
  [[services.ports]]
    handlers = ["http"]
    port = 80
    force_https = true  # optional

TLS handler

The tls handler terminates TLS using Fly.io-managed application certificates, then forwards a plaintext connection to the application process. This is useful for running TCP services and offloading TLS to the Fly Proxy.

For performance purposes, the Fly Proxy will terminate TLS on the host a client connects to, and then forward the connection to the nearest available Machine.

Configuration examples in fly.toml:

[[services]]
...
  [[services.ports]]
    handlers = ["tls", "http"]
    port = 443
    tls_options = { "alpn" = ["h2", "http/1.1"], "versions" = ["TLSv1.2", "TLSv1.3"] }

[http_service]
...
[http_service.tls_options]
  alpn = ["h2", "http/1.1"]
  versions = ["TLSv1.2", "TLSv1.3"]
  default_self_signed = false

Postgres TLS handler

The pg_tls handler manages Postgres connections, so that you can expose your Postgres databases over the proxy securely. Some interesting notes by @glebarez on why standard TLS termination won’t work for Postgres: https://github.com/glebarez/pgssl#readme

Example configuration from default Fly Postgres app fly.toml:

[[services]]
...
  [[services.ports]]
    port = 5433
    handlers = ["pg_tls"]

PROXY protocol handler

The proxy_proto handler adds information about the original connection, including client IP + port and server IP + port (from the client’s perspective). Most apps need additional logic to accept the PROXY protocol, either using a prebuilt library or implementing the PROXY protocol directly.

Fly.io supports version 1 (human-readable header format) of the PROXY protocol by default with the proxy_proto handler. You can configure the proxy_proto handler to use version 2 (binary header format) in the services.ports.proxy_proto_options section of your fly.toml file.

Configuration examples in fly.toml:

[[services.ports]]
  handlers = ["proxy_proto"]
  port = 5000
  proxy_proto_options = { version = "v2" }

HTTP to HTTPS redirects

The force_https configuration option automatically redirects HTTP to HTTPS. When enabled, all HTTP requests return a redirect response with a 301 status code. This option can only be set on HTTP handlers - deployments will fail if set on other handlers.

Outbound IP addresses

Fly Machines have IPv6 addresses from which they make requests to the wider internet without going through the Fly Proxy.

By default, we don’t offer static IPs or regional IP ranges, and we discourage the use of our outbound IPs to bypass firewalls. A Machine’s outbound IP is liable to change without notice. This shouldn’t be a daily occurrence, but it will happen if a Machine is moved for whatever reason, such as a load-balancing of Fly Machines between servers in one region.

If you do need a static outbound IP, you can assign one on a per-machine basis. You can allocate one to a machine with `fly machine egress-ip allocate . This will assign both an IPv4 and IPv6 address to the machine. Like dedicated IPv4 addresses, these are billed monthly.

You can also use the fly machine egress-ip list command to see all the IPs assigned to your machines, and release IPs with fly machine egress-ip release <egress-ip>.

Find your Machine’s outbound IP

The Machine’s outbound IPv6 address is available in the FLY_PUBLIC_IP environment variable. Use fly ssh console -s to get an interactive shell on the Machine of your choice.

echo $FLY_PUBLIC_IP

2605:4c40:92:520a:0:8c93:3d8a:1

You can also call out to an external service that’ll tell you your IP. For example:

curl text.ipv6.wtfismyip.com

2605:4c40:92:520a:0:8c93:3d8a:1

or

dig +short txt o-o.myaddr.l.google.com @ns1.google.com

"2605:4c40:92:520a:0:8c93:3d8a:1"

So this Machine’s outbound IPv6 address is 2605:4c40:92:520a:0:8c93:3d8a:1.

You may have to install software on the Machine to use dig or curl. On Debian, dig belongs to the dnsutils package.

Default-Deny security policy

All requests to Fly.io apps are routed to our edge servers, where we use our memory-safe Rust proxy to direct traffic. The proxy listens on all ports and all Anycast addresses, so ports appear to be ‘open’ from the wider internet. However, nothing on your app is exposed unless you expose it via services. You’re locked down by default.