Docker compose error "In file './docker-compose.yml', service 'punjab' must be a mapping not a string."

Question

I am getting a strange error in my docker-compose.yml file.

I have prepared a docker-compose file for the stack punjab connection manager, ejabberd and mysql.

Below is the docker-compose.yml file

version: '2'
services:
  punjab:
    image:punjab
    ports
     - 5280:5280
    links
     - ejabbberd:ejabberd
  ejabberd:
    image: ejabberd
    depends-on:
      - mysql
    links:
      - mysql:mysql
  mysql:
    image:mysql

When I run the command docker-compose up from the command line and from the same directory where I have the docker-compose.yml file, I get the following error.

ERROR: In file './docker-compose.yml', service 'punjab' must be a mapping not a string.

I parsed the yml file using yamllint as well and the file is correctly formatted.

Answer 1

Although in theory the file format may look correct, there are some things that are wrong.

They are:

1. Use depends_on instead of depends-on because that is the correct syntax.

2. For best practice, use a blank space before informing the image like: image: punjab.

3. On ports and links at punjab service, you forget the colon :

4. The images ejabberd and punjab do not exist on Docker Hub so they must exist in your local repository.

This is an example to use a docker-compose.yml:

version: '2'
services:
  punjab:
    image: punjab
    ports:
      - "5280:5280"
    links:
      - ejabberd

  ejabberd:
    image: ejabberd
    depends_on:
      - mysql
    links:
      - mysql

  mysql:
    image: mysql