Add celery app instance with base config

This patch allows to schedule tasks and launch workers with basic
config. To launch a worker:

    celery -A module_build_service.celery_app -l info

Signed-off-by: Chenxiong Qi <cqi@redhat.com>

conf/config.py

@@ -92,6 +92,18 @@ class BaseConfiguration(object):
     # Disable Client Authorization
     NO_AUTH = False
 
+    # Configs for running tasks asynchronously with Celery
+    # For details of Celery configs, refer to Celery documentation:
+    # https://docs.celeryproject.org/en/latest/userguide/configuration.html
+    #
+    # Each config name consists of namespace CELERY_ and the new Celery config
+    # name converted to upper case. For example the broker url, Celery config
+    # name is broker_url, then as you can below, the corresponding config name
+    # in MBS is CELERY_BROKER_URL.
+    CELERY_BROKER_URL = ""
+    CELERY_RESULT_BACKEND = ""
+    CELERY_IMPORTS = []
+
 
 class TestConfiguration(BaseConfiguration):
     BUILD_LOGS_DIR = "/tmp"
@@ -154,3 +166,6 @@ class OfflineLocalBuildConfiguration(LocalBuildConfiguration):
 class DevConfiguration(LocalBuildConfiguration):
     DEBUG = True
     LOG_BACKEND = "console"
+
+    CELERY_BROKER_URL = "redis://localhost:6379/0"
+    CELERY_RESULT_BACKEND = "redis://localhost:6379/0"

docker/Dockerfile-tests

@@ -43,6 +43,7 @@ RUN yum -y install \
     python-sqlalchemy \
     python-tox \
     python2-distro \
+    python2-celery \
     python2-libmodulemd2 \
     python2-pyyaml \
     python2-pungi \

docker/Dockerfile-tests-py3

@@ -10,6 +10,7 @@ RUN dnf -y install \
     createrepo_c \
     rsync \
     python3-distro \
+    python3-celery \
     python3-fedmsg \
     python3-kobo-rpmlib \
     python3-rpm \

module_build_service/__init__.py

@@ -19,10 +19,12 @@ for a number of tasks:
 """
 
 import pkg_resources
+from celery import Celery
 from flask import Flask, has_app_context, url_for
 from flask_sqlalchemy import SQLAlchemy
 from sqlalchemy.pool import StaticPool
 from logging import getLogger
+
 import gi  # noqa
 gi.require_version("Modulemd", "2.0")  # noqa
 from gi.repository import Modulemd  # noqa
@@ -46,6 +48,15 @@ app.wsgi_app = ReverseProxy(app.wsgi_app)
 
 conf = init_config(app)
 
+celery_app = Celery("module-build-service")
+# Convert config names specific for Celery like this:
+# celery_broker_url -> broker_url
+celery_configs = {
+    name[7:]: getattr(conf, name)
+    for name in dir(conf) if name.startswith('celery_')
+}
+celery_app.conf.update(**celery_configs)
+
 
 class MBSSQLAlchemy(SQLAlchemy):
     """

requirements.txt

@@ -19,3 +19,4 @@ pyOpenSSL
 requests
 six
 sqlalchemy
+celery