vpc_subnet_id needs to be specified

[gavD]

e.g.:

  - name: Launch Instance
    ec2: image='<redacted>'
         instance_type="{{ instance_type }}"
         keypair='dashboard'
         instance_tags='{"Environment":"<redacted>""Class":"<redacted>-immutable","Name":"<redacted> (immutable)"}'
         region='{{ region }}'
         aws_zone='{{ region }}{{ aws_zone }}'
         group_id='<redacted>'
         vpc_subnet_id='<redacted>'
         wait=true
    register: ec2_info

without this, ansible fails, asking about group_id, which is a red herring

[Stillerman]

When using a vpc_subnet_id, you need to use group_id instead of group, and when using ec2 classic you need to use group.