Sandstorm - postgresql not running

Question

I'm trying to port sayIt, a django app with postgresql as a sandstorm app.

I have an instance running on Ubuntu, and using raw packaging to run it in dev mode. However, an error occurs as below:

...** SANDSTORM SUPERVISOR: Starting up grain. Sandbox type: userns
Unhandled exception in thread started by 
Performing system checks...

System check identified no issues (0 silenced).
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/django/utils/autoreload.py", line 229, in wrapper
    fn(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/commands/runserver.py", line 116, in inner_run
    self.check_migrations()
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/commands/runserver.py", line 168, in check_migrations
    executor = MigrationExecutor(connections[DEFAULT_DB_ALIAS])
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 19, in __init__
    self.loader = MigrationLoader(self.connection)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/loader.py", line 47, in __init__
    self.build_graph()
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/loader.py", line 191, in build_graph
    self.applied_migrations = recorder.applied_migrations()
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/recorder.py", line 59, in applied_migrations
    self.ensure_schema()
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/recorder.py", line 49, in ensure_schema
    if self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor()):
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/base.py", line 162, in cursor
    cursor = self.make_debug_cursor(self._cursor())
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/base.py", line 135, in _cursor
    self.ensure_connection()
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/base.py", line 130, in ensure_connection
    self.connect()
  File "/usr/local/lib/python2.7/dist-packages/django/db/utils.py", line 98, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/base.py", line 130, in ensure_connection
    self.connect()
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/base.py", line 119, in connect
    self.connection = self.get_new_connection(conn_params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/postgresql_psycopg2/base.py", line 176, in get_new_connection
    connection = Database.connect(**conn_params)
  File "/usr/local/lib/python2.7/dist-packages/psycopg2/__init__.py", line 164, in connect
    conn = _connect(dsn, connection_factory=connection_factory, async=async)
django.db.utils.OperationalError: could not connect to server: Connection refused
    Is the server running on host "127.0.0.1" and accepting
    TCP/IP connections on port 5432?

I tried to enter the grain, but the document just says read vagrant-spk's source code which I read but can't understand.

It seems like postgresql is not running and listening, but I totally have no idea why. Any hint is appreciated. Thank you!