我的 gitlab-ci.yml 看起來像這樣：stage: functional_test  only:    - develop    - master    - merge_requests  services:    - redis:latest    - docker:18.06.2-dind  variables:    PHOTON_ENV: development    DOCKER_HOST: tcp://localhost:2375    REDIS_HOST: redis    REDIS_URL: redis://redis:6379/0我連接redis的python代碼如下所示：self._redis = redis.Redis(host=_host,                          port=_port,                          db=_db,                          decode_responses=True)_host = 'redis'_port = 6379_db = 0但是，每次我嘗試這段代碼時，都會出現(xiàn)這個錯誤：      File "/usr/local/lib/python3.6/site-packages/redis/client.py", line 772, in execute_command403     connection = pool.get_connection(command_name, **options)404   File "/usr/local/lib/python3.6/site-packages/redis/connection.py", line 994, in get_connection405     connection.connect()406   File "/usr/local/lib/python3.6/site-packages/redis/connection.py", line 497, in connect407     raise ConnectionError(self._error_message(e))408 redis.exceptions.ConnectionError: Error -2 connecting to redis:6379. Name or service not known.