[appendix]
== Migrating from Ranch 2.0 to Ranch 2.1

Ranch 2.1 adds counters and alarms.

The https://github.com/juhlig/prometheus_ranch[Prometheus collector]
was updated to include accepted/terminated connections
metrics.

Ranch 2.1 is compatible with Erlang/OTP 22.0 onward. Support
for Erlang/OTP 21 has been removed.

=== Features added

* Metrics are now provided by `ranch:info/0,1`. Currently
  includes accepted/terminated connection counts per
  connection supervisor.

* Alarms can now be configured. The only alarm currently
  available is `num_connections`. When the number of
  connections goes over a configurable treshold Ranch
  will call the given callback. This can be used to
  programmatically shut down idle connections to
  make up space for new connections, for example.

* A `post_listen` callback option has been added. It
  receives sockets immediately after the `Transport:listen/1`
  call. It can be used for some additional initialization
  of the socket, such as setting file permissions on
  Unix domain sockets.

* It is now possible to use TLS-PSK authentication
  without having to specify a default certificate
  for TLS < 1.3.

=== Experimental features added

* The `inet_backend` option is now properly handled
  and tested for TCP listeners. This allows using
  the experimental `socket` backend. The `socket`
  backend is now tested with Ranch. Note that
  there are known issues and Windows support is not
  currently implemented.

=== Changed behaviors

* Ranch will now remove unsupported SSL/TLS options
  where applicable. A warning will be logged when
  this happens. Options are only removed when they
  are not compatible with the selected TLS version
  and leaving them would prevent the listener from
  starting.
+
  The following options are removed when using TLS
  1.1, 1.2 or 1.3: `beast_mitigation` and `padding_check`.
+
  The following options are removed when using TLS
  1.3 exclusively: `client_renegotiation`,
  `next_protocols_advertised`, `psk_identity`,
  `reuse_session`, `reuse_sessions`,
  `secure_renegotiate` and `user_lookup_fun`.

=== Added functions

* The function `ranch_proxy_header:to_connection_info/1`
  converts PROXY protocol information to the same
  format as `ssl:connection_information/1`. Because
  there is little overlap only the `protocol`,
  `selected_cipher_suite` and `sni_hostname` will
  be available, however.