Currently, the proxy uses a variety of types to represent the logical
destination of a request. Outbound destinations use a `NameAddr` type
which may be either a `DnsNameAndPort` or a `SocketAddr`. Other parts of
the code used a `HostAndPort` enum that always contained a port and also
contained a `Host` which could either be a `dns::Name` or a `IpAddr`.
Furthermore, we coerce these types into a `http::uri::Authority` in many
cases.
All of these types represent the same thing; and it's not clear when/why
it's appropriate to use a given variant.
In order to simplify the situtation, a new `addr` module has been
introduced with `Addr` and `NameAddr` types. A `Addr` may
contain either a `NameAddr` or a `SocketAddr`.
The `Host` value has been removed from the `Settings::Http1` type,
replaced by a boolean, as it's redundant information stored elsewhere in
the route key.
There is one small change in behavior: The `authority` metrics label is
now omitted only for requests that include an `:authority` or `Host`
with a _name_ (i.e. and not an IP address).
The controller's client is instantiated in the
`control::destination::background` module and is tightly coupled to its
use for address resolution.
In order to share this client across different modules---and to bring it
into line with the rest of the proxy's modular layout---the controller
client is now configured and instantiated in `app::main`. The
`app::control` module includes additional stack modules needed to
configure this client.
Our dependency on tower-buffer has been updated so that buffered
services may be cloned.
The `proxy::reconnect` module has been extended to support a
configurable fixed reconnect backoff; and this backoff delay has been
made configurable via the environment.
Oliver Gould