Add support for connecting to nodes by their hostname

Author: janpieper

lib/dns_cluster.ex

@@ -51,7 +51,8 @@ defmodule DNSCluster do
       differs between nodes, a tuple of `{basename, query}` can be provided as well.
       The value `:ignore` can be used to ignore starting the DNSCluster.
     * `:resource_types` - the resource record types that are used for node discovery.
-      Defaults to `[:a, :aaaa]` and also supports the `:srv` type.
+      Defaults to `[:a, :aaaa]` and also supports `{:srv, :ips}`, `{:srv, :hostnames}` and
+      `:srv` (same as `{:srv, :ips}`) type.
     * `:interval` - the millisec interval between DNS queries. Defaults to `5000`.
     * `:connect_timeout` - the millisec timeout to allow discovered nodes to connect.
       Defaults to `10_000`.
@@ -68,7 +69,7 @@ defmodule DNSCluster do
     GenServer.start_link(__MODULE__, opts, name: Keyword.get(opts, :name, __MODULE__))
   end
 
-  @valid_resource_types [:a, :aaaa, :srv]
+  @valid_resource_types [:a, :aaaa, :srv, {:srv, :ips}, {:srv, :hostnames}]
 
   @impl true
   def init(opts) do
@@ -161,7 +162,10 @@ defmodule DNSCluster do
       {basename, addr}
     end
     |> Enum.uniq()
-    |> Enum.map(fn {basename, addr} -> {basename, to_string(:inet.ntoa(addr))} end)
+    |> Enum.map(fn
+      {basename, ip} when is_tuple(ip) -> {basename, to_string(:inet.ntoa(ip))}
+      {basename, hostname} -> {basename, hostname}
+    end)
   end
 
   defp basename_from_query_or_state({basename, _query}, _state), do: basename
@@ -186,7 +190,7 @@ defmodule DNSCluster do
   defp validate_resource_types!(resource_types) do
     if resource_types == [] or resource_types -- @valid_resource_types != [] do
       raise ArgumentError,
-            "expected :resource_types to be a subset of [:a, :aaaa, :srv], got: #{inspect(resource_types)}"
+            "expected :resource_types to be a subset of #{inspect(@valid_resource_types)}, got: #{inspect(resource_types)}"
     end
   end
 

lib/dns_cluster/resolver.ex

@@ -13,30 +13,37 @@ defmodule DNSCluster.Resolver do
 
   def list_nodes, do: Node.list(:visible)
 
-  def lookup(query, type) when is_binary(query) and type in [:a, :aaaa] do
-    case :inet_res.getbyname(~c"#{query}", type) do
-      {:ok, hostent(h_addr_list: addr_list)} -> addr_list
-      {:error, _} -> []
-    end
+  def lookup(query, {:srv, :hostnames}), do: lookup_by_name(query, :srv)
+  def lookup(query, {:srv, :ips}), do: lookup(query, :srv)
+
+  def lookup(query, :srv) do
+    query
+    |> lookup_by_name(:srv)
+    |> Enum.flat_map(&lookup_host_by_name/1)
   end
 
-  def lookup(query, type) when is_binary(query) and type in [:srv] do
-    case :inet_res.getbyname(~c"#{query}", type) do
-      {:ok, hostent(h_addr_list: srv_list)} ->
-        lookup_hosts(srv_list)
+  def lookup(query, resource_type) when resource_type in [:a, :aaaa] do
+    lookup_by_name(query, resource_type)
+  end
 
-      {:error, _} ->
+  defp lookup_by_name(query, resource_type) do
+    case :inet_res.getbyname(~c"#{query}", resource_type) do
+      {:ok, hostent(h_addr_list: addr_list)} ->
+        if resource_type == :srv do
+          for {_prio, _weight, _port, address} <- addr_list, do: address
+        else
+          addr_list
+        end
+
+      {:error, _reason} ->
         []
     end
   end
 
-  defp lookup_hosts(srv_list) do
-    srv_list
-    |> Enum.flat_map(fn {_prio, _weight, _port, host_name} ->
-      case :inet.gethostbyname(host_name) do
-        {:ok, hostent(h_addr_list: addr_list)} -> addr_list
-        {:error, _} -> []
-      end
-    end)
+  defp lookup_host_by_name(query) do
+    case :inet_res.gethostbyname(query) do
+      {:ok, hostent(h_addr_list: addr_list)} -> addr_list
+      {:error, _reason} -> []
+    end
   end
 end

test/dns_cluster_test.exs

@@ -141,7 +141,8 @@ defmodule DNSClusterTest do
   end
 
   describe "resource_types" do
-    test "resource_types can be a subset of [:a, :aaaa, :srv]", config do
+    test "resource_types can be a subset of [:a, :aaaa, :srv, {:srv, :ips}, {:srv, :hostnames}]",
+         config do
       assert {:ok, _cluster} =
                start_supervised(
                  {DNSCluster,
@@ -152,9 +153,10 @@ defmodule DNSClusterTest do
                )
     end
 
-    test "resource_types can't be outside of [:a, :aaaa, :srv]", config do
+    test "resource_types can't be outside of [:a, :aaaa, :srv, {:srv, :ips}, {:srv, :hostnames}]",
+         config do
       assert_raise RuntimeError,
-                   ~r/expected :resource_types to be a subset of \[:a, :aaaa, :srv\]/,
+                   ~r/expected :resource_types to be a subset of \[:a, :aaaa, :srv, {:srv, :ips}, {:srv, :hostnames}\]/,
                    fn ->
                      start_supervised!(
                        {DNSCluster,
@@ -168,7 +170,7 @@ defmodule DNSClusterTest do
 
     test "resource_types can't be empty", config do
       assert_raise RuntimeError,
-                   ~r/expected :resource_types to be a subset of \[:a, :aaaa, :srv\]/,
+                   ~r/expected :resource_types to be a subset of \[:a, :aaaa, :srv, {:srv, :ips}, {:srv, :hostnames}\]/,
                    fn ->
                      start_supervised!(
                        {DNSCluster,