aquatic: high-performance BitTorrent tracker

Blazingly fast, multi-threaded BitTorrent tracker written in Rust, consisting of sub-implementations for different protocols:

Name	Protocol	OS requirements
aquatic_udp	BitTorrent over UDP	Unix-like
aquatic_http	BitTorrent over HTTP with TLS (rustls)	Linux 5.8+
aquatic_ws	WebTorrent over TLS (rustls)	Unix-like with mio (default) / Linux 5.8+ with glommio

Usage

Prerequisites

• Install Rust with rustup (stable is recommended)
• Install cmake with your package manager (e.g., apt-get install cmake)
• Unless you're planning to only run the cross-platform mio based implementations, make sure locked memory limits are sufficient. You can do this by adding the following lines to /etc/security/limits.conf, and then logging out and back in:

*    hard    memlock    512
*    soft    memlock    512

• Clone this git repository and enter it

Compiling

Compile the implementations that you are interested in:

# Tell Rust to enable support for all CPU extensions present on current CPU
# except for those relating to AVX-512. This is necessary for aquatic_ws and
# recommended for the other implementations.
. ./scripts/env-native-cpu-without-avx-512

cargo build --release -p aquatic_udp
cargo build --release -p aquatic_http
cargo build --release -p aquatic_ws
cargo build --release -p aquatic_ws --features "with-glommio" --no-default-features

Running

Begin by generating configuration files. They differ between protocols.

./target/release/aquatic_udp -p > "aquatic-udp-config.toml"
./target/release/aquatic_http -p > "aquatic-http-config.toml"
./target/release/aquatic_ws -p > "aquatic-ws-config.toml"

Make adjustments to the files. You will likely want to adjust address (listening address) under the network section.

Note that both aquatic_http and aquatic_ws require configuring TLS certificate and private key files. More details are available in the respective configuration files.

Once done, run the tracker:

./target/release/aquatic_udp -c "aquatic-udp-config.toml"
./target/release/aquatic_http -c "aquatic-http-config.toml"
./target/release/aquatic_ws -c "aquatic-ws-config.toml"

Configuration values

Starting more socket_workers than request_workers is recommended. All implementations are quite IO-bound and spend a lot of their time reading from and writing to sockets. This is handled by the socket workers, which also do parsing, serialisation and access control. They pass announce and scrape requests to the request workers, which update internal tracker state and pass back responses for sending.

Access control

Access control by info hash is supported for all protocols. The relevant part of configuration is:

[access_list]
# Access list mode. Available modes are white, black and off.
mode = "off"
# Path to access list file consisting of newline-separated hex-encoded info hashes.
path = ""

The file is read on start and when the program receives SIGUSR1. If initial parsing fails, the program exits. Later failures result in in emitting of an error-level log message, while successful updates of the access list result in emitting of an info-level log message.

Architectural overview

Details on implementations

aquatic_udp: UDP BitTorrent tracker

Implements:

• BEP 015: UDP BitTorrent tracker protocol (more details). Exceptions:
  • Doesn't care about IP addresses sent in announce requests. The packet source IP is always used.
  • Doesn't track of the number of torrent downloads (0 is always sent).
• IPv6 support

IPv4 and IPv6 peers are tracked separately.

This is the most mature of the implementations. I consider it ready for production use.

Performance

More details are available here.

Optimisation attempts that didn't work out

• Using glommio
• Using io-uring
• Using zerocopy + vectored sends for responses
• Using sendmmsg

aquatic_http: HTTP BitTorrent tracker

Implements:

• BEP 003: HTTP BitTorrent protocol (more details). Exceptions:
  • Only runs over TLS
  • Doesn't track of the number of torrent downloads (0 is always sent)
  • Only compact responses are supported
• BEP 023: Compact HTTP responses
• BEP 007: IPv6 support
• BEP 048: HTTP scrape support. Notes:
  • Doesn't allow full scrapes, i.e. of all registered info hashes

IPv4 and IPv6 peers are tracked separately.

aquatic_http has not been tested as much as aquatic_udp but likely works fine.

aquatic_ws: WebTorrent tracker

Aims for compatibility with WebTorrent clients. Notes:

• Only runs over TLS
• Doesn't track of the number of torrent downloads (0 is always sent).
• Doesn't allow full scrapes, i.e. of all registered info hashes

IPv4 and IPv6 peers are tracked separately.

aquatic_ws has not been tested as much as aquatic_udp but likely works fine.

Load testing

There are load test binaries for all protocols. They use a CLI structure similar to the trackers and support generation and loading of configuration files.

To run, first start the tracker that you want to test. Then run the corresponding load test binary:

./scripts/run-load-test-udp.sh
./scripts/run-load-test-http.sh
./scripts/run-load-test-ws.sh

To fairly compare HTTP performance to opentracker, set keepalive to false in aquatic_http settings.

Copyright and license

Copyright (c) 2020-2022 Joakim Frostegård

Distributed under Apache 2.0 license (details in LICENSE file.)

Trivia

The tracker is called aquatic because it thrives under a torrent of bits ;-)