Configuration File

YAML File Format

The Bang configuration file structure came about with the following goals in mind:

• Readability (by humans)
• Not another bespoke serialization format
• Conciseness

While JSON would allow for there to be one less package dependency, YAML was chosen as the overall serialization format because of its focus on human readability.

In its earliest forms, Bang had its own SSH logic and used Chef for configuration management. When Ansible was identified as being a suitable replacement for the builtin SSH logic and for Chef, it made even more sense to continue using YAML for the file format because users could use the same format for configuring Bang and for authoring Ansible playbooks.

Stepped Input Format

Both Bang and Ansible use YAML as their input file formats. However, the logical structure of the input in Bang is different enough from that of Ansible to be jarring to end users.

Whereas Ansible’s input consists of a set of steps that are executed in order, Bang’s input is a declaration of state without control of execution order.

To reconcile this difference and to allow end users finer-grained control of execution order, Bang should accept the following, new, stepped format:

- stack:
    name: my_three_tier_site
    version: 0.1

- servers:
    masterdb:
      hostname: really.its_publicly_accessible.com

- playbooks:
  - register_masterdb_dns_alias.yml
  - monitor_masterdb.yml

- config_scopes:
    masterdb:
      username: threetier
      password: tierthree
    webapp:
      package:
        name: my_biz_logic
        version: 0.1.2
      debug: false

- servers:
    webapplb:
      groups:
      - common
      - haproxy
      provider: aws
      region_name: us-west-2
      availability_zone: us-west-2b
      instance_type: t1.micro
      disk_image_id: ami-ed2864dd  # debian wheezy 64-bit (2014-10-24)
      ssh_key_name: deployer
      launch_timeout_s: 120
      aws:
        instance_profile_name: webapplb

    webapp:
      groups:
      - common
      - my_biz_logic
      provider: aws
      region_name: us-west-2
      availability_zone: us-west-2b
      instance_type: m3.large
      instance_count: 10
      disk_image_id: ami-ed2864dd  # debian wheezy 64-bit (2014-10-24)
      ssh_key_name: deployer
      launch_timeout_s: 120
      aws:
        instance_profile_name: webapp
      config_scopes:
      - masterdb
      - webapp

- playbooks:
  - common.yml
  - webapplb.yml
  - webapp.yml