# `Ankusa.Sink.Connections`
[🔗](https://github.com/jamescarr/ankusa/blob/ankusa-v0.7.0/packages/ankusa/lib/ankusa/sink/connections.ex#L1)

The broker connections a sink adapter opens on demand. An adapter package
starts one tree with `start_link/1` from its `Application`: a
`DynamicSupervisor` (`<sink>.Supervisor`) that owns the connections and an
`Ankusa.Sink.Reaper` (`<sink>.Reaper`) that closes idle ones, under
`<sink>.TopSup`. A sink calls `ensure/5` before every publish.

The connections live in the adapter's tree, not the instance's, so a lost
broker never takes ingest or dispatch down: it makes `publish/4` (see
`Ankusa.Sink.Messaging`) return `{:error, _}` for the source's
`Ankusa.RetryPolicy`. A connection that belongs to one instance registers
through that instance's registry (`Ankusa.via/2`, found again with
`Ankusa.whereis/2`), so nothing is registered globally and two instances
never share one; core itself does not know which adapters are loaded.

# `ensure`

```elixir
@spec ensure(
  module(),
  term(),
  (-&gt; pid() | nil),
  (-&gt; Supervisor.child_spec()),
  non_neg_integer()
) ::
  {:ok, pid()} | {:error, term()}
```

The connection `key` names, started on demand and about to be used.

`lookup` finds the running one (`Ankusa.whereis/2`, `Process.whereis/1`);
`nil` starts `child.()` under `sink`'s supervisor — only then is the child
spec built, and a start that loses the race (`{:error, {:already_started,
pid}}`) is that pid. The pid is touched in `sink`'s reaper under `key` with
`idle_ms` (`Ankusa.Sink.Reaper.touch/4`; `0` never reaps), so `key` is
printed when the connection is closed and must carry no credential.

# `reaper`

```elixir
@spec reaper(module()) :: atom()
```

The reaper (and its table) that closes `sink`'s idle connections.

# `start_link`

```elixir
@spec start_link(module()) :: Supervisor.on_start()
```

Start `sink`'s connection tree; an adapter's `Application.start/2` returns this.

# `supervisor`

```elixir
@spec supervisor(module()) :: atom()
```

The `DynamicSupervisor` that owns `sink`'s connections.

---

*Consult [api-reference.md](api-reference.md) for complete listing*