error to connect master

I used below docker-compose file to start a new citus db , and it can't start up
```
version: '2.1'
services:
master:
container_name: "crawlerapp_citus_master"
image: 'citusdata/citus:7.0.2'
ports: ["5435:5432"]
labels: ['com.citusdata.role=Master']
worker:
image: 'citusdata/citus:7.0.2'
labels: ['com.citusdata.role=Worker']
depends_on:
- manager
manager:
container_name: "crawlerapp_citus_manager"
image: 'citusdata/membership-manager:0.2.0'
volumes: ['/var/run/docker.sock:/var/run/docker.sock']
depends_on:
- master
```
Error:
```
crawlerapp_citus_manager | 2017-10-12T08:59:22.076391668Z Traceback (most recent call last):
crawlerapp_citus_manager | 2017-10-12T08:59:22.076416025Z File "./manager.py", line 97, in
crawlerapp_citus_manager | 2017-10-12T08:59:22.076568390Z main()
crawlerapp_citus_manager | 2017-10-12T08:59:22.076581185Z File "./manager.py", line 93, in main
crawlerapp_citus_manager | 2017-10-12T08:59:22.076629913Z docker_checker()
crawlerapp_citus_manager | 2017-10-12T08:59:22.076637428Z File "./manager.py", line 60, in docker_checker
crawlerapp_citus_manager | 2017-10-12T08:59:22.076795199Z conn = connect_to_master()
crawlerapp_citus_manager | 2017-10-12T08:59:22.076803122Z File "./manager.py", line 47, in connect_to_master
crawlerapp_citus_manager | 2017-10-12T08:59:22.076889557Z (postgres_db, postgres_user, citus_host, postgres_pass))
crawlerapp_citus_manager | 2017-10-12T08:59:22.076898633Z File "/usr/local/lib/python3.6/site-packages/psycopg2/__init__.py", line 130, in connect
crawlerapp_citus_manager | 2017-10-12T08:59:22.077069013Z conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
crawlerapp_citus_manager | 2017-10-12T08:59:22.077076586Z psycopg2.OperationalError: could not translate host name "master" to address: Name does not resolve
```
This error happens in my cloud server, it's OK in my local mac machine,

Start with manager.py, especially connect_to_master and the docker_checker call shown in the traceback, then compare the provided docker-compose service and dependency configuration between the local Mac and cloud server. Reproduce the startup failure in the cloud environment; done means the manager can resolve and connect to the master service and the stack starts without the psycopg2 hostname error.

Written by the indexing model from the issue text.