distributor_frontend.py

import redis
DISTRIBUTED_CACHE_TOP_PHRASES_KEY = 'top-phrases:'

class Frontend:

	def __init__(self):
		self._distributed_cache = redis.Redis(host=os.getenv("DISTRIBUTED_CACHE_HOST"), port=6379, db=0)

	# Using Cache Aside Pattern
	def top_phrases_for_prefix(self, prefix):
		top_phrases_from_distributed_cache = self._top_phrases_for_prefix_distributed_cache(prefix)
		if (top_phrases_from_distributed_cache is not None):
			return top_phrases_from_distributed_cache
		
		backend_hostname = self.backend_for_prefix(prefix)
		r = requests.get(f'http://{backend_hostname}:6000/top-phrases', params = {'prefix': prefix})
		top_phrases = r.json()["data"]["top_phrases"]
		self._insert_top_phrases_distributed_cache(prefix, top_phrases)
    
		return top_phrases

	def _top_phrases_for_prefix_distributed_cache(self, prefix):
		key = DISTRIBUTED_CACHE_TOP_PHRASES_KEY + prefix
		self._logger.debug(f'Attempting to get top phrases from distributed cache with key {key}')
		if (self._distributed_cache.exists(key)):
			pickled_list = self._distributed_cache.get(key)
			return pickle.loads(pickled_list)
		return None

	def _insert_top_phrases_distributed_cache(self, prefix, top_phrases):
		key = DISTRIBUTED_CACHE_TOP_PHRASES_KEY + prefix
		time_to_expire_s = 30 * 60 # Expire entry after 30 minutes
		self._logger.debug(f'Inserting top phrases tokey {key}, with top phrases {top_phrases}')
		self._distributed_cache.set(key, pickle.dumps(top_phrases), ex=time_to_expire_s)

docker-compose.yml

  distributor.distributed-cache:
    container_name: distributor.distributed-cache
    image: redis:6.0.6
    ports:
      - "6379:6379"