== Embedded mode
Embedded mode allows you to insert Ranch listeners directly
in your supervision tree. This allows for greater fault tolerance
control by permitting the shutdown of a listener due to the
failure of another part of the application and vice versa.
=== Embedding
To embed Ranch in your application you can simply add the child specs
to your supervision tree. This can all be done in the `init/1` function
of one of your application supervisors.
Ranch requires at the minimum two kinds of child specs for embedding.
First, you need to add `ranch_sup` to your supervision tree, only once,
regardless of the number of listeners you will use. Then you need to
add the child specs for each listener.
Ranch has a convenience function for getting the listeners child specs
called `ranch:child_spec/6`, that works like `ranch:start_listener/6`,
except that it doesn't start anything, it only returns child specs.
As for `ranch_sup`, the child spec is simple enough to not require a
convenience function.
The following example adds both `ranch_sup` and one listener to another
application's supervision tree.
.Embed Ranch directly in your supervision tree
[source,erlang]
----
init([]) ->
RanchSupSpec = {ranch_sup, {ranch_sup, start_link, []},
permanent, 5000, supervisor, [ranch_sup]},
ListenerSpec = ranch:child_spec(echo, 100,
ranch_tcp, [{port, 5555}],
echo_protocol, []
),
{ok, {{one_for_one, 10, 10}, [RanchSupSpec, ListenerSpec]}}.
----
Remember, you can add as many listener child specs as needed, but only
one `ranch_sup` spec!
It is recommended that your architecture makes sure that all listeners
are restarted if `ranch_sup` fails. See the Ranch internals chapter for
more details on how Ranch does it.
