The mastersrv maintains a list of all registered DDNet (and Teeworlds) servers. Game servers try to register themselves with the mastersrv via an HTTP POST request on /ddnet/15/register. The mastersrv delays the registration until the the game server can prove it actually listens on the provided port (need_challenge). In order to do that, the mastersrv sends a UDP message containing an opaque token to the game server. The game server will include this token in its next register and the register process will succeed (success).

To build the mastersrv, have a recent version of Rust installed and run cargo build --release in the src/mastersrv folder. The resulting binary should appear in src/mastersrv/target/release/mastersrv.

Use --help to see some of the options of the mastersrv.

servers.json

The servers.json file produced by the mastersrv is not actually served automatically, it needs to be served by another HTTPS server, probably by the same as the reverse proxy handling HTTPS for the mastersrv. It is suggested to serve the servers.json file at the path /ddnet/15/servers.json.

Logs

To enable logs, set the environment variable RUST_LOG=mastersrv,info. Logs should appear already when just starting the mastersrv.

Reverse proxy

In order to run this mastersrv in production, you must put it behind a reverse proxy that handles HTTPS, such as nginx, Caddy, or Apache.

This means the mastersrv cannot determine the origin IP address by looking at the IP address of the request, it will come from the reverse proxy, likely on localhost. The mastersrv expects that the reverse proxy adds a header where it puts the original requester IP address, e.g. Connecting-IP. Add --connecting-ip-header Connecting-IP to the command line options of the mastersrv.

For nginx, add proxy_set_header Connecting-IP $remote_addr;

For Caddy, add header_up Connecting-IP {http.request.remote}.

For Apache, run a2enmod headers and add RequestHeader set Connecting-IP "%{REMOTE_ADDR}s" to the config.

If you're behind Cloudflare, instead use --connecting-ip-header CF-Connecting-IP without any changes.