New example: Distributed task queue

Adds an example of using Kubernetes to build a distributed task queue
using Celery along with a RabbitMQ broker and Flower frontend.

Resolves: #1788

examples/celery-rabbitmq/celery-app-add/Dockerfile

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+FROM dockerfile/celery
+
+ADD celery_conf.py /data/celery_conf.py
+ADD run_tasks.py /data/run_tasks.py
+ADD run.sh /usr/local/bin/run.sh
+
+ENV C_FORCE_ROOT 1
+
+CMD ["/bin/bash", "/usr/local/bin/run.sh"]

examples/celery-rabbitmq/celery-app-add/celery_conf.py

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+import os
+
+from celery import Celery
+
+# Get Kubernetes-provided address of the broker service
+broker_service_host = os.environ.get('RABBITMQ_SERVICE_SERVICE_HOST')
+
+app = Celery('tasks', broker='amqp://guest@%s//' % broker_service_host, backend='amqp')
+
+@app.task
+def add(x, y):
+    return x + y
+

examples/celery-rabbitmq/celery-app-add/run.sh

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+#!/bin/bash
+
+# Copyright 2014 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Run the celery worker
+/usr/local/bin/celery -A celery_conf worker -f /data/celery.log &
+
+# Start firing periodic tasks automatically
+python /data/run_tasks.py

examples/celery-rabbitmq/celery-app-add/run_tasks.py

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+import random
+import syslog
+import time
+
+from celery_conf import add
+
+while True:
+    x = random.randint(1, 10)
+    y = random.randint(1, 10)
+    res = add.delay(x, y)
+    time.sleep(5)
+    if res.ready():
+        res.get()