pgsql: move logic out of watcher, wire mode of operation

lib/ha_handler/pgsql.ex

@@ -1,10 +1,45 @@
 defmodule HAHandler.PGSQL do
 	@supervisor HAHandler.PGSQL.Supervisor
+	@version_query "SELECT version();"
+	@is_in_recovery_query "SELECT pg_is_in_recovery();"
 
-	def status() do
+	def get_instances() do
 		watchers = Supervisor.which_children(@supervisor)
-		for {_id, pid, _type, _modules} <- watchers do
-			GenServer.call(pid, :status)
+		for {hostname, pid, _type, _modules} <- watchers do
+			{hostname, pid}
 		end
 	end
+
+	def get_version({hostname, pid}) do
+		case GenServer.call(pid, {:execute, @version_query, []}) do
+			{:ok, %Postgrex.Result{rows: [[raw_version_string]]}} ->
+				version = case Regex.run(~r/^PostgreSQL (\d+\.\d+)/, raw_version_string) do
+					[_, version_number] -> version_number
+					_ -> "unknown"
+				end
+				%{hostname: hostname, version: version, status: "up"}
+			{:error, %DBConnection.ConnectionError{message: _msg, reason: err}} ->
+				%{hostname: hostname, version: "unknown", status: err}
+			_ ->
+				%{hostname: hostname, version: "unknown", status: :unknown}
+		end
+	end
+
+	def get_operation_mode({_hostname, pid}) do
+		case GenServer.call(pid, {:execute, @is_in_recovery_query, []}) do
+			{:ok, %Postgrex.Result{rows: [[false]]}} ->
+				:primary
+			{:ok, %Postgrex.Result{rows: [[true]]}} ->
+				:secondary
+			_ ->
+				:unknown
+		end
+	end
+
+	def get_stats() do
+		get_instances()
+		|> Enum.map(fn instance ->
+			get_version(instance) |> Map.put(:mode, get_operation_mode(instance))
+		end)
+	end
 end

lib/ha_handler/pgsql/supervisor.ex

@@ -9,7 +9,12 @@ defmodule HAHandler.PGSQL.Supervisor do
 
 	@impl true
 	def init(instances) do
-		children = Enum.map(instances, fn conf -> {PGSQLWatcher, conf} end)
+		children = Enum.map(instances, fn conf ->
+			%{
+				id: Keyword.get(conf, :hostname),
+				start: {PGSQLWatcher, :start_link, [conf]}
+			}
+		end)
 
 		opts = [ strategy: :one_for_one ]
 		Supervisor.init(children, opts)

lib/ha_handler/pgsql/watcher.ex

@@ -3,7 +3,7 @@ defmodule HAHandler.PGSQL.Watcher do
 	require Logger
 
 	def start_link(opts) do
-		GenServer.start_link(__MODULE__, opts, name: __MODULE__)
+		GenServer.start_link(__MODULE__, opts)
 	end
 
 	@impl true
@@ -23,20 +23,7 @@ defmodule HAHandler.PGSQL.Watcher do
 	end
 
 	@impl true
-	def handle_call(:status, _from, %{backend: backend, hostname: hostname} = state) do
-		result = case Postgrex.query(backend, "SELECT version();", []) do
-			{:ok, %Postgrex.Result{rows: [[raw_version_string]]}} ->
-				version = case Regex.run(~r/^PostgreSQL (\d+\.\d+)/, raw_version_string) do
-					[_, version_number] -> version_number
-					_ -> "unknown"
-				end
-				%{hostname: hostname, version: version, status: "up"}
-			{:error, %DBConnection.ConnectionError{message: _msg, reason: err}} ->
-				%{hostname: hostname, version: "unknown", status: err}
-			_ ->
-				%{hostname: hostname, version: "unknown", status: "Unhandled error"}
-		end
-
-		{:reply, result, state}
+	def handle_call({:execute, query, params}, _from, %{backend: backend} = state) do
+		{:reply, Postgrex.query(backend, query, params), state}
 	end
 end

lib/ha_handler/web/controller.ex

@@ -19,9 +19,12 @@ defmodule HAHandler.Web.Controller do
 	def index(conn) do
 		{:ok, hostname} = :net_adm.dns_hostname(:net_adm.localhost)
 
+		haproxy_stats = HAProxy.get_stats([hide_error: true])
+		pgsql_stats = PGSQL.get_stats()
+
 		assigns = [
-			haproxy_stats: HAProxy.get_stats([hide_error: true]),
-			pgsql_status: PGSQL.status(),
+			haproxy_stats: haproxy_stats,
+			pgsql_status: pgsql_stats,
 			hostname: hostname,
 			otp_app: HAHandler.otp_app(),
 			version: HAHandler.version(),

lib/ha_handler/web/templates/index.html.eex

@@ -109,6 +109,7 @@
 						<th>Hostname</th>
 						<th>Version</th>
 						<th>Status</th>
+						<th>Operation</th>
 					</tr>
 				</thead>
 				<tbody>
@@ -117,6 +118,7 @@
 							<td><%= entry[:hostname] %></td>
 							<td><%= entry[:version] %></td>
 							<td><%= entry[:status] %></td>
+							<td><%= entry[:mode] %></td>
 						</tr>
 					<% end %>
 				</tbody>