docker-compose creating multiple instances for the same image

Question

I need to start multiple containers for the same image. If i create my compose file as shown below, it works fine.

version: '2'

services:
  app01:
    image: app
  app02:
    image: app
  app03:
    image: app
  app04:
    image: app
  app05:
    image: app  

Is there any easy way for me to mention the number of instances for the compose instead of copy and pasting multiple times?

Answer 1

Updated answer (Oct 2017)

As others mentioned, the docker API has changed. I'm updating my answer since it's the one most people will probably look at.

docker-compose up -d --scale app=5

Unfortunately, we cannot specify this in a docker-compose.yml file currently (as of version 3.5).

Details:
They did introduce the scale option for version 2.2 and 2.3 of docker-compose but removed it for version 3.0. Also, to use version 2.2 or 2.3 you would need to download an older version of the docker-compose tool. The current version does not support 2.2 or 2.3 (it does support 2.0 or 2.1 however). There is also a new deploy section with replicas: 5 but it's only for swarm mode.

--- Old Answer --------------------------------------

docker-compose scale app=5

See https://docs.docker.com/compose/reference/scale/

Then you only need this docker-compose file

version: '2'

services:
  app:
    image: app