Migrating from Ranch 1.7+ to Ranch 2.0

Ranch 2.0 adds support for multiple connection supervisors.

Ranch 1.x had a bottleneck because it used only a single connection supervisor. This was more evident when many connections were dropped at once as the supervisor couldn't keep up and failed to accept new connections while cleaning up the old ones. Ranch 2.0 behaves much better in this scenario by default. Multiple connection supervisors also helps with concurrently accepting new connections.

Ranch 2.0 also adds experimental support for opening more than one listening socket on a single port.

Starting with Ranch 2.0 we are also providing a Prometheus collector as a separate project as well as a Grafana dashboard.

Ranch 2.0 is compatible with Erlang/OTP 21.0 onward. Support for Erlang/OTP 19 and 20 has been removed.

Features added

• Ranch now comes with a ranch.appup file necessary for performing release upgrades. A test suite has been added to confirm release upgrades work from one tag to the next. Numerous fixes were made that will also improve error recovery. Release upgrades will only be supported from Ranch 2.0 onward.
• The num_conns_sups option has been added. It allows configuring the number of connection supervisors. It now defaults to num_accceptors. The old behavior can be obtained by setting this value to 1.
• The logger option is no longer experimental. It now defaults to logger instead of error_logger.
• UNIX domain sockets are now supported.
• The active N socket option is now supported. It requires Erlang/OTP 21.3 or above for TLS, however.
• Embedded listeners are now failing in a predictable manner when ranch_server goes down. It is no longer necessary to embed ranch_sup and the recommendation is now to just start Ranch normally when using embedded listeners.
• Two steps handshake is now supported. This allows obtaining TLS extensions and updating options before resuming the handshake. The handshake can also be canceled.

Experimental features added

• The experimental num_listen_sockets option has been added. It allows opening more than one listening socket per listener. It can only be used alongside the Linux SO_REUSEPORT socket option or equivalent. It allows working around a bottleneck in the kernel and maximizes resource usage, leading to increased rates for accepting new connections.

Features removed

• The socket option was removed. A more viable solution is to define a custom transport module that returns a fresh socket when Transport:listen/1 is called.

Changed behaviors

• The callback function Transport:listen/1 and its implementations in ranch_tcp and ranch_ssl have changed to accept a map of transport options instead of only socket options.
• The callback function Transport:messages/0 return value now includes the tag used for passive messages.
• The Socket argument was removed from Protocol:start_link/3. The socket must now be obtained by calling ranch:handshake/1,2.

Added functions

• The functions ranch:handshake_continue/1,2 and ranch:handshake_cancel/1 can be used to perform a two steps handshake. These functions may not be supported by all transports.

Changed functions

• The NumAcceptors argument was removed from ranch:start_listener/5 and ranch:child_spec/5 and moved to the transport options.
• Ranch options can no longer be passed along with socket options as a proplist. The only forms allowed are now the ranch:opts() map or only socket options as-is. Individual transport options are now validated as well. The ranch:opts() map must be used when socket options also use a map. This applies to the ranch:start_listener/5, ranch:child_spec/5 and ranch:set_transport_options/2 functions.
• The function ranch:info/1,2 now returns a map containing each listener's information rather than a list of key/values. The key num_acceptors was removed as it can be found in the transport options.
• The function ranch:set_transport_options/2 no longer requires the listener to be suspended. Which options apply immediately, on suspend/resume or on restart has been documented. Some work has also been done to make these option changes more predictable.

Removed functions

• The function ranch:accept_ack/1 has been removed in favor of ranch:handshake/1,2.

Bugs fixed

• Calling ranch:remove_connection/1 will now resume a sleeping acceptor process when applicable.
• Repeatedly calling ranch:remove_connection/1 from a connection process would crash the respective connection supervisor. This has now been fixed.
• When a connection process was failing to start, the socket was not closed and this lead to leaking sockets. This is now corrected.

Other changes

• Connection draining has now been documented in the guide following user feedback and discussions.
• Ranch is now tested against Concuerror, a model checking tool for debugging, testing and verifying concurrent Erlang programs. Two tests have been added in this release and more will follow in the future.
• Ranch is now tested against stampede, a chaos monkey style testing tool. Currently includes three scenarios: normal TCP and TLS listeners and embedded TCP listener. This new test suite helped uncover a misplaced monitor/2 call added during the development of Ranch 2.0 (we were using a similar tool, havoc, at the time of finding that issue).
• The supervisor for acceptors and the parent supervisor for connection supervisors now have an adaptive restart intensity limit set to 1 + ceil(math:log2(NumChildren)) to allow room for errors when they have many children.
• Ranch now uses stricter compiler options. Missing function specs were added to internal modules.
• Ranch now calls ssl:handshake/1,2,3 instead of ssl:ssl_accept/1,2.
• The ranch_ssl:ssl_opt() type has been updated to conform with Erlang/OTP 23.0.