How to use Flask/Peewee with Heroku?

Question

I am attempting to deploy a Flask app to Heroku. I'm using Peewee as an ORM for a Postgres database. When I follow the standard Heroku steps to deploying Flask, the web process crashes after I enter heroku ps:scale web=1. Here's what the logs say:

Starting process with command `python app.py`
/app/.heroku/venv/lib/python2.7/site-packages/peewee.py:2434: UserWarning: Table for <class 'flask_peewee.auth.User'> ("user") is reserved, please override using Meta.db_table
cls, _meta.db_table,
Traceback (most recent call last):
File "app.py", line 167, in <module>
auth.User.create_table(fail_silently=True)
File "/app/.heroku/venv/lib/python2.7/site-packages/peewee.py", line 2518, in create_table if fail_silently and cls.table_exists():
File "/app/.heroku/venv/lib/python2.7/site-packages/peewee.py", line 2514, in table_exists return cls._meta.db_table in cls._meta.database.get_tables()
File "/app/.heroku/venv/lib/python2.7/site-packages/peewee.py", line 507, in get_tables ORDER BY c.relname""")
File "/app/.heroku/venv/lib/python2.7/site-packages/peewee.py", line 313, in execute cursor = self.get_cursor()
File "/app/.heroku/venv/lib/python2.7/site-packages/peewee.py", line 310, in get_cursor return self.get_conn().cursor()
File "/app/.heroku/venv/lib/python2.7/site-packages/peewee.py", line 306, in get_conn self.connect()
File "/app/.heroku/venv/lib/python2.7/site-packages/peewee.py", line 296, in connect self.__local.conn = self.adapter.connect(self.
database, **self.connect_kwargs)
File "/app/.heroku/venv/lib/python2.7/site-packages/peewee.py", line 199, in connect return psycopg2.connect(database=database, **kwargs)
File "/app/.heroku/venv/lib/python2.7/site-packages/psycopg2/__init__.py", line 179, in connect connection_factory=connection_factory, async=async)
psycopg2.OperationalError: could not connect to server: No such file or directory
Is the server running locally and accepting connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
Process exited with status 1
State changed from starting to crashed

I've tried a bunch of different things to get Heroku to allow my app to talk to a Postgres db, but haven't had any luck. Is there an easy way to do this? What do I need to do to configure Flask/Peewee so that I can use a db on Heroku?

Answer 1

According to the Peewee docs, you don't want to use Proxy() unless your local database driver is different than your remote one (i.e. locally, you're using SQLite and remotely you're using Postgres). If, however, you are using Postgres both locally and remotely it's a much simpler change. In this case, you'll want to only change the connection values (database name, username, password, host, port, etc.) at runtime and do not need to use Proxy().

Peewee has a built-in URL parser for database connections. Here's how to use it:

import os
from peewee import *
from playhouse.db_url import connect

db = connect(os.environ.get('DATABASE_URL'))

class BaseModel(Model):
    class Meta:
        database = db

In this example, peewee's db_url module reads the environment variable DATABASE_URL and parses it to extract the relevant connection variables. It then creates a PostgresqlDatabase object with those values.

Locally, you'll want to set DATABASE_URL as an environment variable. You can do this according to the instructions of whatever shell you're using. Or, if you want to use the Heroku toolchain (launch your local server using heroku local) you can add it to a file called .env at the top level of your project. For the remote setup, you'll want to add your database URL as a remote Heroku environment variable. You can do this with the following command:

heroku config:set DATABASE_URL=postgresql://myurl

You can find that URL by going into Heroku, navigating to your database, and clicking on "database credentials". It's listed under URI.

Answer 2

heroku config:set HEROKU=1

import os
import urlparse
import psycopg2
from flask import Flask
from flask_peewee.db import Database


if 'HEROKU' in os.environ:
    DEBUG = False
    urlparse.uses_netloc.append('postgres')
    url = urlparse.urlparse(os.environ['DATABASE_URL'])
    DATABASE = {
        'engine': 'peewee.PostgresqlDatabase',
        'name': url.path[1:],
        'user': url.username,
        'password': url.password,
        'host': url.hostname,
        'port': url.port,
    }
else:
    DEBUG = True
    DATABASE = {
        'engine': 'peewee.PostgresqlDatabase',
        'name': 'framingappdb',
        'user': 'postgres',
        'password': 'postgres',
        'host': 'localhost',
        'port': 5432 ,
        'threadlocals': True
    }

app = Flask(__name__)
app.config.from_object(__name__)
db = Database(app)

Modified coleifer's answer to answer hasenj's comment. Please mark one of these as the accepted answer.

Answer 3

Are you parsing the DATABASE_URL environment variable? It will look something like this:

postgres://username:password@host:port/database_name

So you will want to pull that in and parse it before you open a connection to your database. Depending on how you've declared your database (in your config or next to your wsgi app) it might look like this:

import os
import urlparse

urlparse.uses_netloc.append('postgres')
url = urlparse.urlparse(os.environ['DATABASE_URL'])

# for your config
DATABASE = {
    'engine': 'peewee.PostgresqlDatabase',
    'name': url.path[1:],
    'password': url.password,
    'host': url.hostname,
    'port': url.port,
}

See the notes here: https://devcenter.heroku.com/articles/django

Answer 4

I have managed to get my Flask app which uses Peewee working on Heroku using the below code:

# persons.py

import os
from peewee import *

db_proxy = Proxy()

# Define your models here
class Person(Model):
    name = CharField(max_length=20, unique=True)
    age  = IntField()

    class Meta:
        database = db_proxy

# Import modules based on the environment.
# The HEROKU value first needs to be set on Heroku
# either through the web front-end or through the command
# line (if you have Heroku Toolbelt installed, type the following:
# heroku config:set HEROKU=1).
if 'HEROKU' in os.environ:
    import urlparse, psycopg2
    urlparse.uses_netloc.append('postgres')
    url = urlparse.urlparse(os.environ["DATABASE_URL"])
    db = PostgresqlDatabase(database=url.path[1:], user=url.username, password=url.password, host=url.hostname, port=url.port)
    db_proxy.initialize(db)
else:
    db = SqliteDatabase('persons.db')
    db_proxy.initialize(db)

if __name__ == '__main__':
    db_proxy.connect()
    db_proxy.create_tables([Person], safe=True)

You should already have a Postgres database add-on attached to your app. You can do this via the command line or through the web front-end. Assuming that the database is already attached to your app and you have already deployed your with the above changes, log-in to Heroku and create the table(s):

$ heroku login
$ heroku run bash
$ python persons.py

Check that the table was created:

$ heroku pg:psql
your_app_name::DATABASE=> \dt 

You then import this file (persons.py in this example) in another Python script, e.g. a request handler. You need to manage the database connection explicitly:

# server.py

from flask import g
from persons import db_proxy

@app.before_request
def before_request():
    g.db = db_proxy
    g.db.connect()

@app.after_request
def after_request(response):
    g.db.close()
    return response

…

References:

• https://devcenter.heroku.com/articles/heroku-postgresql
• http://peewee.readthedocs.org/en/latest/peewee/database.html#dynamically-defining-a-database
• http://peewee.readthedocs.org/en/latest/peewee/example.html#establishing-a-database-connection
• https://stackoverflow.com/a/20131277/3104465
• https://gist.github.com/fprieur/9561148