add handler for SIGUSR1 to start drying up calls, useful as a generic mechanism on non-AWS deployments (#1482)

lib/utils/sbc-pinger.js

@@ -100,6 +100,39 @@ module.exports = (logger) => {
   else if (K8S) {
     lifecycleEmitter.scaleIn = () => process.exit(0);
   }
+  else {
+    process.on('SIGUSR1', () => {
+      logger.info('received SIGUSR1: begin drying up calls for scale-in');
+      dryUpCalls = true;
+
+      const {srf} = require('../..');
+      const {writeSystemAlerts} = srf.locals;
+      if (writeSystemAlerts) {
+        const {SystemState, FEATURE_SERVER} = require('./constants');
+        writeSystemAlerts({
+          system_component: FEATURE_SERVER,
+          state : SystemState.GracefulShutdownInProgress,
+          fields : {
+            detail: `feature-server with process_id ${process.pid} shutdown in progress`,
+            host: srf.locals?.ipv4
+          }
+        });
+      }
+      pingProxies(srf);
+
+      // if we have zero calls, we can complete the scale-in right
+      setTimeout(() => {
+        const calls = srf.locals.sessionTracker.count;
+        if (calls === 0) {
+          logger.info('scale-in can complete immediately as we have no calls in progress');
+          process.exit(0);
+        }
+        else {
+          logger.info(`${calls} calls in progress; scale-in will complete when they are done`);
+        }
+      }, 5000);
+    });
+  }
 
 
   async function pingProxies(srf) {