docker-compose.yml

version: '2'
 services:
 api:
 build: .
 links:
 - mongo:mongo
 ports:
 - 9527:9527
 restart: unless-stopped
 volumes:
 - $PWD:/usr/src/app/
 env_file:
 - .env
 environment:
 - MONGO_HOST=mongodb://mongo/api
 hostname: api
 depends_on:
 - mongo
 mongo:
 image: bitnami/mongodb:latest
 hostname: mongo
 restart: unless-stopped
 ports:
 - 27017:27017

Api container’s/etc/hosts

127.0.0.1       localhost
 ::1     localhost ip6-localhost ip6-loopback
 fe00::0 ip6-localnet
 ff00::0 ip6-mcastprefix
 ff02::1 ip6-allnodes
 ff02::2 ip6-allrouters
 172.18.0.3      api

Mongo container/etc/hosts

127.0.0.1       localhost
 ::1     localhost ip6-localhost ip6-loopback
 fe00::0 ip6-localnet
 ff00::0 ip6-mcastprefix
 ff02::1 ip6-allnodes
 ff02::2 ip6-allrouters
 172.18.0.2      mongo

There is no problem in creating, but according to my understanding, it should be inapiContainer/etc/hostsCreate an alias, the result is no, just created the container’s own