backwater

Backwater - Intercluster RPC for Erlang and Elixir

backwater allows you to call remote modules without depending on the Erlang distribution protocol.

It's targeted at scenarios where nodes in one datacenter need to call nodes in another datacenter, over unsecure or unstable networks.

Usage

Run make console to bring up a shell. We're going to expose the string module and call it remotely.

1. Generate a secret

Secret = crypto:strong_rand_bytes(32).

2. Start the server

backwater:start_clear_server(Secret, [string]).
% {ok, _ServerPid}

3. Execute a remote call

backwater:call({"127.0.0.1", Secret}, string, to_upper, ["hello"]).
% {ok, "HELLO"}

Details

backwater is built on top of cowboy and hackney.

Requirements

Erlang/OTP 20 or higher
rebar3

For Erlang/OTP 18 support, check the 1.1.x versions. For Erlang/OTP 19 support, check the 2.x, 3.0.x, 3.1.x or 3.2.x versions.

All requests and responses are authenticated and signed using a modified version of HTTP signatures; nevertheless, it's strongly recommended to use HTTPS, as HTTP signatures offer no protection against replay attacks - besides risking exposure of sensitive data.

Exceptions

By default, remote exceptions are returned as errors on the caller's side. This behaviour can be tweaked using the rethrow_remote_exceptions flag in :call/5 options.

Remote stack traces are returned by default. Because they are computationally expensive to generate, this behaviour can be can be changed using the return_exception_stacktraces flag in :start_clear_server / :start_tls_server backwater options.

Serialisation

The external term format is used for all function arguments and return values.

Because trust is assumed unless declared otherwise (like in regular Erlang clusters), unsafe terms are decoded by default.

For function arguments, this behaviour can be tweaked through the decode_unsafe_terms setting in backwater options when running :start_clear_server or :start_tls_server.

For return values, this behaviour can be tweaked through the decode_unsafe_terms setting in :call/5 options.

Compression

By default, both serialised function arguments and serialised return values larger than 300 bytes are subject to attempted compression using gzip. The actual compression result is only used if it is indeed smaller than the original payload.

For function arguments, this threshold can be tweaked through the compression_threshold setting in :call/5 options.

For return values, this threshold can be tweaked through the compression_threshold setting in backwater options when running :start_clear_server or :start_tls_server.

Payload limits

By default, both serialised function arguments and serialised return values larger than 8 MiB are rejected (independently of whether they're transmitted in compressed form or not.)

For function arguments, this limit (in bytes) can be adjusted using the max_encoded_args_size setting in backwater options when running :start_clear_server or :start_tls_server.

For return values, this limit (in bytes) can be adjusted using the max_encoded_result_size setting in :call/5 options.

Timeouts and ports

The default listen port for HTTP is 8080; for HTTPS, it's 8443. This can be adjusted on server using the http options, and on clients by specifying it in Endpoint.

The client enforces a default connection timeout of 8s, and a receive timeout of 5s. Either can be adjusted using either connect_timeout or recv_timeout, respectively, in :call/5 options.

The server enforces a default receive timeout of 5s. This can be adjusted using the recv_timeout setting in backwater options, when running :start_clear_server or :start_tls_server.

On using alternative HTTP clients

For now, the best way to achieve this is to build requests using the backwater_request module and interpret responses using the backwater_response module.

License

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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