docker-compose image named: "prefix_%s_1" instead of "%s"

Question

When I set up a couple of Docker containers in docker-compose.yaml file with links, the name of the containers ends up being of the format prefix_%s_1 instead of %s, and the alias in /etc/hosts on the linking container is the same.

Why is the alias of the redis container test_redis_1 instead of redis?

Here are the relevant files and output:

# docker-compose.yaml
monkey:
    build: ../../monkey
    dockerfile: test.Dockerfile
    links:
      - redis:redis
    ports:
      - "9006:9006"

redis:
    build: ../storage/redis
    ports:
      - "6379:6379"

After running docker-compose build && docker-compose up:

$ docker-compose ps
Name           Command                        State  Ports
---------------------------------------------------------------------------
test_redis_1   redis-server /usr/local/et ...   Up   0.0.0.0:6379->6379/tcp
test_monkey_1  python -m SimpleHTTPServer ...   Up   0.0.0.0:9006->9006/tcp

Output from the test_monkey_1 container:

Step 14 : RUN cat /etc/hosts
 ---> Running in 1c104e3d9bf5
172.17.1.26     75a485df1325
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
172.17.1.26     thirsty_lumiere.bridge
172.17.0.220    test_redis_1
172.17.0.220    test_redis_1.bridge
172.17.1.26     thirsty_lumiere
 ---> 3a06bac9b3ca
Removing intermediate container 1c104e3d9bf5
Step 15 : RUN echo
 ---> Running in a1c5b5f8ae0f

 ---> 385c9ee44332
Removing intermediate container a1c5b5f8ae0f
Step 16 : RUN ifconfig eth0 | grep inet addr
 ---> Running in 17cd638c6473
          inet addr:172.17.1.28  Bcast:0.0.0.0  Mask:255.255.0.0
 ---> 21235e29abc1
Removing intermediate container 17cd638c6473
Step 17 : RUN echo
 ---> Running in 8c0b1db2a69b

 ---> e2dd190eb4d1
Removing intermediate container 8c0b1db2a69b
Step 18 : RUN env
 ---> Running in 50cd1b6bf9da
HOSTNAME=75a485df1325
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PWD=/data/web/tunnelbear.com/play/tPWD=/data/web/tunnelbear.com/root
_=/usr/bin/env

Answer 1

According to docker compose issue #745:

By default, Compose bases the project name on basename of the directory compose commands are run from. The project name can be overridden either by passing a -p / --project-name option for each command or setting the COMPOSE_PROJECT_NAME environment variable.

You can set the prefix of your choice to your container names by writing something like this:

$ docker-compose -p MY_PROJECT_NAME 

which is the equivalent to (the more readable):

$ docker-compose --project-name MY_PROJECT_NAME 

Answer 2

You could just set container name to what you want via container_name:

redis:
    build: ../storage/redis
    container_name: redis
    ports:
      - "6379:6379"

And container hostname could also be set via hostname.

Answer 3

Docker compose will use the name of the directory with your compose file as the name of the project unless you set if via the -p option

-p, --project-name NAME     Specify an alternate project name (default: directory name)

Compose supports declaring default environment variables in an environment file named .env placed in the folder where the docker-compose command is executed (current working directory).

Where you'll want to set COMPOSE_PROJECT_NAME