support drain/undrain feature server from cluster

lib/http-routes/api/cluster.js

@@ -0,0 +1,24 @@
+const router = require('express').Router();
+const {srf} = require('../../..');
+
+router.post('/drain', async(req, res) => {
+  const {logger} = req.app.locals;
+  const {setDryUpCalls} = srf.locals;
+
+  logger.info('Received drain request via HTTP API');
+  setDryUpCalls();
+
+  res.sendStatus(201);
+});
+
+router.post('/undrain', async(req, res) => {
+  const {logger} = req.app.locals;
+  const {clearDryUpCalls} = srf.locals;
+
+  logger.info('Received undrain request via HTTP API');
+  clearDryUpCalls();
+
+  res.sendStatus(201);
+});
+
+module.exports = router;