Ansible: Dynamic Inventory (using the AWS EC2 External Inventory Script)

Where hosts can appear and disappear (e.g. with AWS ASGs) the EC2 external inventory script (ec2.py) comes in useful.

All you need to do is to export your AWS keys as environment variables and ec2.py is good.

ec2.ini options

The EC2 inventory output can become very large. To manage its size, you can configure which groups should be created using ec2.ini options. E.g.

group_by_instance_id = False
group_by_region = False
group_by_availability_zone = False
group_by_ami_id = False
group_by_instance_type = False
group_by_key_pair = False
group_by_vpc_id = False
group_by_security_group = False
group_by_tag_keys = True
group_by_tag_none = True
group_by_route53_names = True
group_by_rds_engine = True
group_by_rds_parameter_group = False

Note on how these are created:

  • format is tag_KEY_VALUE
  • special characters are changed to an underscore

E.g. with a NAME of my instance name we would get a tag of  tag_NAME_my_instance_name.

 

These inikeys are read in ec2.py. E.g.

        # Configure which groups should be created.
        group_by_options = [
            'group_by_instance_id',
            'group_by_region',
            'group_by_availability_zone',
            'group_by_ami_id',
            'group_by_instance_type',
            'group_by_instance_state',
            'group_by_key_pair',
            'group_by_vpc_id',
            'group_by_security_group',
            'group_by_tag_keys',
            'group_by_tag_none',
            'group_by_route53_names',
            'group_by_rds_engine',
            'group_by_rds_parameter_group',
            'group_by_elasticache_engine',
            'group_by_elasticache_cluster',
            'group_by_elasticache_parameter_group',
            'group_by_elasticache_replication_group',
            'group_by_aws_account',
        ]
        for option in group_by_options:
            if config.has_option('ec2', option):
                setattr(self, option, config.getboolean('ec2', option))
            else:
                setattr(self, option, True)

See also:

https://github.com/ansible/ansible/blob/devel/contrib/inventory/ec2.py#L482

and

https://docs.ansible.com/ansible/2.6/user_guide/intro_dynamic_inventory.html#example-aws-ec2-external-inventory-script

 

 

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