- Latest release:
- Branch status (
master
): - Branch status (
develop
): - Issues:
- License:
- Erlang Factory 2016 Talk
To build this project you need to have the following:
-
Erlang/OTP >= 19.1
-
git >= 1.7
-
GNU make >= 3.80
-
rebar3 >= 3.2
Getting started with gen_rpc
is easy. First, add the appropriate dependency line to your rebar.config
:
{deps, [
{gen_rpc, {git, "https://github.com/priestjim/gen_rpc.git", {branch, "master"}}}
]}.
Or if you're using hex.pm
/rebar3
:
{deps [
{gen_rpc, "~> 2.0"}
]}.
Or if you're using Elixir/Mix:
def project do
[
deps: [
{:gen_rpc, "~> 2.0"}
]
]
Then, add gen_rpc
as a dependency application to your .app.src
/.app
file:
{application, my_app, [
{applications, [kernel, stdlib, gen_rpc]}
]}
Or your mix.exs
file:
def application do
applications: [:gen_rpc]
end
Finally, start a couple of nodes to test it out:
(my_app@127.0.0.1)1> gen_rpc:call('other_node@1.2.3.4', erlang, node, []).
'other_node@1.2.3.4'
gen_rpc
implements only the subset of the functions of the rpc
library that make sense for the problem it's trying to solve. The library's function interface and return values is 100% compatible with rpc
with only one addition: Error return values include {badrpc, Error}
for RPC-based errors but also {badtcp, Error}
for TCP-based errors.
For more information on what the functions below do, run erl -man rpc
.
-
call(NodeOrNodeAndKey, Module, Function, Args)
andcall(NodeOrNodeAndKey, Module, Function, Args, Timeout)
: A blocking synchronous call, in thegen_server
fashion. -
cast(NodeOrNodeAndKey, Module, Function, Args)
: A non-blocking fire-and-forget call. -
async_call(NodeOrNodeAndKey, Module, Function, Args)
,yield(Key)
,nb_yield(Key)
andnb_yield(Key, Timeout)
: Promise-based calls. Make a call withasync_call
and retrieve the result asynchronously, when you need it withyield
ornb_yield
. -
multicall(Module, Function, Args)
,multicall(Nodes, Module, Function, Args)
,multicall(Module, Function, Args, Timeout)
andmulticall(NodesOrNodesWithKeys, Module, Function, Args, Timeout)
: Multi-node version of thecall
function. -
abcast(NodesOrNodesWithKeys, Name, Msg)
andabcast(Name, Msg)
: An asynchronous broadcast function, sending the messageMsg
to the named processName
in all the nodes inNodesOrNodesWithKeys
. -
sbcast(NodesOrNodesWithKeys, Name, Msg)
andsbcast(Name, Msg)
: A synchronous broadcast function, sending the messageMsg
to the named processName
in all the nodes inNodesOrNodesWithKeys
. Returns the nodes in which the named process is alive and the nodes in which it isn't. -
eval_everywhere(Module, Function, Args)
andeval_everywhere(NodesOrNodesWithKeys, Module, Function, Args)
: Multi-node version of thecast
function.
gen_rpc
supports multiple outgoing connections per node using a key of arbitrary type to differentiate between connections.
To leverage this feature, replace Node
in your calls (single-node and multi-node alike) with {Node, Key}
. The Key
is hashed using erlang:phash2/1
, attached to the client process name and a new connection is initiated.
Attention: When using functions that call gen_rpc:nodes/0
implicitly (such as gen_rpc:multicall/3
), the channels
used to communicate to the nodes are the keyless ones. To leverage the sharded functionality, pre-create your {Node, Key}
lists
and pass them as the node list in the multi-node function.
gen_rpc
supports executing RPC calls on remote nodes that are running only specific module versions. To leverage that feature, in place of Module
in the section above, use {Module, Version}
. If the remote module
is not on the version requested a {badrpc,incompatible]
will be returned.
-
tcp_server_port
: The plain TCP portgen_rpc
will use for incoming connections orfalse
if you do not want plain TCP enabled. -
tcp_client_port
: The plain TCP portgen_rpc
will use for outgoing connections. -
ssl_server_port
: The portgen_rpc
will use for incoming SSL connections orfalse
if you do not want SSL enabled. -
ssl_client_port
: The portgen_rpc
will use for outgoing SSL connections. -
ssl_server_options
andssl_client_options
: Settings for thessl
interface thatgen_rpc
will use to connect to a remotegen_rpc
server. -
default_client_driver
: The default drivergen_rpc
is going to use to connect to remotegen_rpc
nodes. It should be eithertcp
orssl
. -
client_config_per_node
: A map ofNode => {Driver, Port}
orNode => Port
that instructsgen_rpc
on thePort
and/orDriver
to use when connecting to aNode
. If you prefer to use an external discovery service to mapNodes
to{Driver, Port}
tuples, instead of the map, you'll need to define a{Module, Function}
tuple instead with a function that takes theNode
as its single argument, consumes the external discovery service and returns a{Driver, Port}
tuple. -
rpc_module_control
: Set it toblacklist
to define a list of modules that will not be exposed togen_rpc
or towhitelist
to define the list of modules that will be exposed togen_rpc
. Set it todisabled
to disable this feature. -
rpc_module_list
: The list of modules that are going to be blacklisted or whitelisted. -
authentication_timeout
: Default timeout for the authentication state of an incoming connection in milliseconds. Used to protect against half-open connections in a DoS attack. -
connect_timeout
: Default timeout for the initial node-to-node connection in milliseconds. -
send_timeout
: Default timeout for the transmission of a request (call
/cast
etc.) from the local node to the remote node in milliseconds. -
call_receive_timeout
: Default timeout for the reception of a response in acall
in milliseconds. -
sbcast_receive_timeout
: Default timeout for the reception of a response in ansbcast
in milliseconds. -
client_inactivity_timeout
: Inactivity period in milliseconds after which a client connection to a node will be closed (and hence have the TCP file descriptor freed). -
server_inactivity_timeout
: Inactivity period in milliseconds after which a server port will be closed (and hence have the TCP file descriptor freed). -
async_call_inactivity_timeout
: Inactivity period in milliseconds after which a pending process holding anasync_call
return value will exit. This is used for process sanitation purposes so please make sure to set it in a sufficiently high number (orinfinity
). -
socket_keepalive_idle
: Seconds idle after the last packet of data sent to start sending keepalive probes (applies to both drivers). -
socket_keepalive_interval
: Seconds between keepalive probes. -
socket_keepalive_count
: Probs lost to consider the socket closed
gen_rpc
uses hut for logging. This allows the developer to integrate the logging library of their choice by providing the appropriate definition in their rebar.config
. The default logging facility of hut
is SASL.
For more information on how to enable gen_rpc
to use your own logging facility, consult the README.md of hut
.
gen_rpc
supports SSL for inter-node communication. This allows secure communication and execution over insecure channels such as the internet, essentially allowing a trully globally distributed Erlang/Elixir setup. gen_rpc
is very opinionated on how SSL should be configured and the bundled default options include:
-
A proper PFS-enabled cipher suite
-
Both server and client-based SSL node CN (Common Name) verification
-
Secure renegotiation
-
TLS 1.1/1.2 enforcement
All of these settings can be found in include/ssl.hrl
and overriden by redefining the necessary option in ssl_client_options
and ssl_server_options
. To actually use SSL support, you'll need to define in both ssl_client_options
and ssl_server_options
:
-
The public and private keys in PEM format, for the node you're running
gen_rpc
on, using the usualcertfile
,keyfile
options. -
The public key of the CA that signs the node's key and the public key(s) of CA that
gen_rpc
should trust, included in the filecacertfile
points at. -
Optionally, a Diffie-Hellman parameter file using the
dhfile
option.
To generate your own self-signed CA and node certificates, numerous articles can be found online such as this.
Usually, the CA that will be signing your client and server SSL certificates will be the same so a nominal sys.confg
that includes SSL support for gen_rpc
will look like:
{gen_rpc, [
{ssl_client_options, [
{certfile, "priv/cert.pem"},
{keyfile, "priv/cert.key"},
{cacertfile, "priv/ca.pem"},
{dhfile, "priv/dhparam.pem"}
]},
{ssl_server_options, [
{certfile, "priv/cert.pem"},
{keyfile, "priv/cert.key"},
{cacertfile, "priv/ca.pem"},
{dhfile, "priv/dhparam.pem"}
]}
]}
For multi-site deployments, a performant setup can be provisioned with edge gen_rpc
nodes using SSL over the internet and plain TCP for internal data exchange. In that case, non-edge nodes can have {ssl_server_port, false}
and {default_client_driver, tcp}
and edge nodes can have their plain TCP port firewalled externally and {default_client_driver, ssl}
.
gen_rpc
can call an external module to provide driver/port mappings in case you want to use an external discovery service like etcd
for node configuration management. The module should implement the gen_rpc_external_source
behaviour which takes the Node
as an argument and should return either {Driver, Port}
(Driver
being tcp
or ssl
and Port
being the port the remote node's
gen_rpc
's driver is listening in) or {error, Reason}
(if the service is unavailable). To set it, change client_config_per_node
from the default of {internal, #{}}
to {external, ModuleName}
where ModuleName
is the module that implements the gen_rpc_external_source
behaviour.
gen_rpc
bundles a Makefile
that makes development straightforward.
To build gen_rpc
simply run:
make
To run the full test suite, run:
make test
To run the full test suite, the XRef tool and Dialyzer, run:
make dist
To build the project and drop in a console while developing, run:
make shell-master
or
make shell-slave
If you want to run a "master" and a "slave" gen_rpc
nodes to run tests.
To clean every build artifact and log, run:
make distclean
A full suite of tests has been implemented for gen_rpc
. You can run the CT-based test suite, dialyzer and xref by:
make dist
If you have Docker available on your system, you can run dynamic integration tests with "physically" separated hosts/nodes by running the command:
make integration
This will launch 3 slave containers and 1 master (change that by NODES=5 make integration
) and will run the integration_SUITE
CT test suite.
TL;DR: gen_rpc
uses a mailbox-per-node architecture and gen_tcp
processes to parallelize data reception from multiple nodes without blocking the VM's distributed port.
The reasons for developing gen_rpc
became apparent after a lot of trial and error while trying to scale a distributed Erlang infrastructure using the rpc
library initially and subsequently erlang:spawn/4
(remote spawn). Both these solutions suffer from very specific issues under a sufficiently high number of requests.
The rpc
library operates by shipping data over the wire via Distributed Erlang's ports into a registered gen_server
on the other side called rex
(Remote EXecution server), which is running as part of the standard distribution. In high traffic scenarios, this allows the inherent problem of running a single gen_server
server to manifest: mailbox flooding. As the number of nodes participating in a data exchange with the node in question increases, so do the messages that rex
has to deal with, eventually becoming too much for the process to handle (don't forget this is confined to a single thread).
Enter erlang:spawn/4
(remote spawn from now on). Remote spawn dynamically spawns processes on a remote node, skipping the single-mailbox restriction that rex
has. The are various libraries written to leverage that loophole (such as Rexi), however there's a catch.
Remote spawn was not designed to ship large amounts of data as part of the call's arguments. Hence, if you want to ship a large binary such as a picture or a transaction log (large can also be small if your network is slow) over remote spawn, sooner or later you'll see this message popping up in your logs if you have subscribed to the system monitor through erlang:system_monitor/2
:
{monitor,<4685.187.0>,busy_dist_port,#Port<4685.41652>}
This message essentially means that the VM's distributed port pair was busy while the VM was trying to use it for some other task like Distributed Erlang heartbeat beacons or mnesia synchronization. This of course wrecks havoc in certain timing expectations these subsystems have and the results can be very problematic: the VM might detect a node as disconnected even though everything is perfectly healthy and mnesia
might misdetect a network partition.
gen_rpc
solves both these problems by sharding data coming from different nodes to different processes (hence different mailboxes) and by using a different gen_tcp
port for different nodes (hence not utilizing the Distributed Erlang ports).
In order to achieve the mailbox-per-node feature, gen_rpc
uses a very specific architecture:
-
Whenever a client needs to send data to a remote node, it will perform a
whereis
to a process named after the remote node. -
If the specified
client
process does not exist, it will request for a new one through thedispatcher
process, which in turn will launch it through the appropriateclient
supervisor. Since this |whereis
> request from dispatcher sequence > start client| can happen concurrently by many different processes, serializing it behind agen_server
allows us to avoid race conditions. -
The
dispatcher
process will launch a newclient
process through the client's supervisor. -
The new client process will connect to the remote node's
gen_rpc server
, submit a request for a new server and wait. -
The
gen_rpc server
server will ask theacceptor
supervisor to launch a newacceptor
process and hands it off the new socket connection. -
The
acceptor
takes over the new socket and authenticates theclient
with the current Erlang cookie and any extra protocol-level authentication supported by the selected driver. -
The
client
finally encodes the request (call
,cast
etc.) along with some metadata (the caller's PID and a reference) and sends it over the TCP channel. In case of anasync call
, theclient
also launches a process that will be responsible for handing the server's reply to the requester. -
The
acceptor
on the other side decodes the TCP message received and spawns a new process that will perform the requested function. By spawning a process external to the server, theacceptor
protects itself from misbehaving function calls. -
As soon as the reply from the server is ready (only needed in
async_call
andcall
), theacceptor
spawned process messages the server with the reply, theacceptor
ships it through the TCP channel to theclient
and the client send the message back to the requester. In the case ofasync call
, theclient
messages the spawned worker and the worker replies to the caller with the result.
All gen_tcp
processes are properly linked so that any TCP failure will cascade and close the TCP channels and any new connection will allocate a new process and port.
An inactivity timeout has been implemented inside the client
and server
processes to free unused TCP connections after some time, in case that's needed.
gen_rpc
is being used in production extensively with over 150.000 incoming calls/sec/node on a 8-core Intel Xeon E5 CPU and Erlang 19.1. The median payload size is 500 KB. No stability or scalability issues have been detected in over a year.
- When shipping an anonymous function over to another node, it will fail to execute because of the way Erlang implements anonymous functions (Erlang serializes the function metadata but not the function body). This issue also exists in both
rpc
and remote spawn.
This project is published and distributed under the Apache License.
Please see CONTRIBUTING.md