ruby - docker-compose: connection refused between containers, but service accessible from host -

tl;dr: how have change below docker-compose.yml in order allow 1 container use service of on custom (non-standard) port?

i have pretty common setup: containers web app (padrino [ruby]), postgres, redis, , queueing framework (sidekiq). web app comes custom dockerfile, remaining services come either standard images (postgres, redis), or mount data web app (sidekiq). ties via following docker-compose.yml:

version: '2'  services:   web:     build: .     command: 'bundle exec puma -c config/puma.rb'     volumes:       - .:/myapp     ports:       - "9000:3000"     depends_on:       - postgres       - redis    sidekiq:     build: .     command: 'bundle exec sidekiq -c config/sidekiq.yml -r ./config/boot.rb'     volumes:       - .:/myapp     depends_on:       - postgres       - redis    postgres:     image: postgres:9.5     environment:       postgres_user: my-postgres-user       postgres_password: my-postgres-pass     ports:       - '9001:5432'     volumes:       - 'postgres:/var/lib/postgresql/data'    redis:     image: redis     ports:       - '9002:6379'     volumes:       - 'redis:/var/lib/redis/data'  volumes:   redis:   postgres: 

one key point notice here exposing containers services on non-standard ports (9000-9002).

if start setup docker-compose up, redis , postgres containers come fine, containers web app , sidekiq fail since can't connect redis @ redis:9002. remarkably enough, same setup works if use 6379 (the standard redis port) instead of 9002.

docker ps looks fine afaik:

container id        image                   command                  created                  status              ports                              names 9148566c2509        redis                   "docker-entrypoint.sh"   less second ago   minute   0.0.0.0:9002->6379/tcp             rubydockerpadrino_redis_1 e6d47321c939        postgres:9.5            "/docker-entrypoint.s"   less second ago   minute   0.0.0.0:9001->5432/tcp             rubydockerpadrino_postgres_1 

what's more confusing: can access redis container from host via redis-cli -h localhost -p 9002 -n 0, web app , sidekiq containers fail establish connection.

i using docker version on macos: docker version 1.12.3, build 6b644ec, experimental

any ideas doing wrong? i'd appreciate hint how setup running.

when bind ports '9002:6379' you're telling docker forward traffic localhost:9002 -> redis:6379. that's why works host machine:

redis-cli -h localhost -p 9002 -n 0 

however, when containers talk each other, connected same network default (the docker bridge or docker0). default, containers can communicate each other freely on network, without needing ports opened. within network, redis container listening traffic on it's usual port (6379), host isn't involved @ all. that's why container container communication works on 6379.