slt is a dead-simple TLS reverse-proxy with SNI multiplexing (TLS virtual hosts).

That means you can send TLS/SSL connections for multiple different applications to the same port and forward them all to the appropriate backend hosts depending on the intended destination.

Features

SNI Multiplexing

slt multiplexes connections to a single TLS port by inspecting the name in the SNI extension field of each connection.

Simple YAML Configuration

You configure slt with a simple YAML configuration file:

bind_addr: ":443"

frontends:
  v1.example.com:
    backends:
      -
        addr: ":4443"

  v2.example.com:
    backends:
      -
        addr: "192.168.0.2:443"
      -
        addr: "192.168.0.1:443"

Optional TLS Termination

Sometimes, you don't actually want to terminate the TLS traffic, you just want to forward it elsewhere. slt only terminates the TLS traffic if you specify a private key and certificate file like so:

frontends:
  v1.example.com:
    tls_key: /path/to/v1.example.com.key
    tls_crt: /path/to/v1.example.com.crt

ALPN Filtering

You can restrict a frontend to only forward connections that advertise a specific ALPN protocol. If alpn is not specified, all connections are forwarded regardless of ALPN (default behavior).

Single ALPN:

frontends:
  v1.example.com:
    alpn: h2
    backends:
      -
        addr: ":5443"

Multiple ALPNs:

frontends:
  v1.example.com:
    alpn:
      - h2
      - http/1.1
    backends:
      -
        addr: ":5443"

Connections whose ClientHello does not contain any of the configured ALPN protocols will be rejected.

Round robin load balancing among arbitrary backends

slt performs simple round-robin load balancing when more than one backend is available (other strategies will be available in the future):

frontends:
  v1.example.com:
    backends:
      -
        addr: ":8080"
      -
        addr: ":8081"

Running it

Running slt is also simple. It takes a single argument, the path to the configuration file:

./slt /path/to/config.yml

Building it

Just cd into the directory and "go build". It requires Go 1.1+.

Cross-compile with GoReleaser (snapshot)

goreleaser build --snapshot --clean

Testing it

Just cd into the directory and "go test".

Stability

I run slt in production handling hundreds of thousands of connections daily.

License

Apache