How can I ping other containers in a docker network through their hostname?

delete this network_mode: bridge from your compose file, worked for me =).

Credits to tgogos: I just had to use the non-default bridge.

For completeness, here is my working config.

version: "3"
services:
  main:
    networks:
      test:
    image: python:3.5.2
    entrypoint: /usr/bin/yes

  another:
    networks:
      test:
    image: python:3.5.2
    entrypoint: /usr/bin/yes


networks:
  test:
    driver: bridge

And the ping now works.

$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
faa9f96d46a9        python:3.5.2        "/usr/bin/yes"      9 seconds ago       Up 9 seconds                            dockerplayground_main_1
5b2d56ac0cd7        python:3.5.2        "/usr/bin/yes"      9 seconds ago       Up 8 seconds                            dockerplayground_another_1
$ docker exec -it faa ping another
PING another (172.18.0.2): 56 data bytes
64 bytes from 172.18.0.2: icmp_seq=0 ttl=64 time=0.054 ms
64 bytes from 172.18.0.2: icmp_seq=1 ttl=64 time=0.047 ms
64 bytes from 172.18.0.2: icmp_seq=2 ttl=64 time=0.059 ms
64 bytes from 172.18.0.2: icmp_seq=3 ttl=64 time=0.066 ms

Another solution I tried and worked was explicitly linking the containing you want to ping with host name. For example, I have a postgres container, and a server wants to connect to it.

Run the server with the following

docker run --name server --link postgres someserver:latest

In the server container environment, you can then ping with (given postgres is on the same bridge/network and is running)

ping postgres 

Since --link has been deprecated, it is recommended to use network bridge.

docker network create YOURNETWORK
docker run --name postgres --network='YOURNETWORK' postgres:latest
docker run --name server --network='YOURNETWORK' server:latest

then the two containers can ping each other by name.