Implement a drain script for postgres 10 properly use the fast shutdown mode

Co-authored-by: Benjamin Gandon <benjamin.gandon@sap.com>

Author: mvach

jobs/postgres-10/spec

@@ -7,6 +7,7 @@ templates:
   create-database.erb: bin/create-database
   postgres.erb: bin/postgres
   postgresql.conf.erb: config/postgresql.conf
+  drain.erb: bin/drain
 
 packages:
   - postgres-10

jobs/postgres-10/templates/drain.erb

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+
+# If a command fails, in a pipeline or not, exit immediately
+set -e -o pipefail
+
+function prepend_datetime() {
+  awk -W interactive '{ system("echo -n [$(date +%FT%T%z)]"); print " " $0 }'
+}
+
+# Before redirecting stdout and stderr, copy the file descriptor for original
+# stdout where BOSH is expecting an integer, and only that.
+exec 3>&1
+exec \
+    1> >(prepend_datetime >> /var/vcap/sys/log/postgres-10/drain.out.log) \
+    2> >(prepend_datetime >> /var/vcap/sys/log/postgres-10/drain.err.log)
+
+output_for_bosh() {
+    exit_code=$?
+
+    if [ $exit_code -eq 0 ]; then
+        echo "postgres-10 deamon is properly shutdown with Fast Shutdown mode (SIGINT)"
+    else
+        echo "drain failed"
+    fi
+
+    echo $exit_code >&3
+}
+
+trap output_for_bosh EXIT
+
+
+postgres_pid=$(/var/vcap/packages/bpm/bin/bpm pid postgres-10)
+kill -s SIGINT "${postgres_pid}"