hostdb 0.0.1

Hostdb helps with terraform machien allocation and ansible inventory

hostdb

This is an ansible plugin library that provides custom functionality to use terraform as inventory in ansible playbooks. This also helps with terraform machine management to define machines using a proper naming scheme. The original intended use case was for proxmox VMs, though can be used with other terraform providers.

Details

This library provides an ansibile inventory plugin powered by the terraform database. Hosts are provisioned and updated in terraform, then can be used to power ansible inventory.

This library also contains modules useful for allocating new hostnames, and generally validating that the host database is setup correctly.

Machine naming

Machines are allocated following A Proper Server Naming Scheme that helps us treat our machines like cattle, but still find them. The basics are:

• You have a domain name that all hosts are assigned to e.g. example.com
• Every host assigned a name from a wordlist, however we don't have to care about it in practice. e.g. blast.example.com
• A site has a geograph e.g. lax.example.com
• Every machine has one or more purposes (e.g. a service that it runs) and has a CNAME for each. Serial numbers are added to identify the service. e.g. mon01.lax.example.com

Hostnames are allocated using a wordlist hostdb/resources/wordlist which are reasonably interesting names recommended from the naming scheme above.

This is just a quick summary, but see the above article for more details.

Database format

This inventory module expects to have the following output variables in outputs.tf:

output "hosts" {
  description = "All allocated hostnames (including retired)"
  value = local.all_hosts
}

output "node_ids" {
  description = "A map of hosts to proxmox VM node ids"
  value = module.vms.node_id
}

output "services" {
  description = "Assignments for all services"
  value = var.services
}

An example of a hosts output looks something like the following:

"blast": {
    "ip": "192.168.1.80",
},
"domino": {
    "ip": "192.168.1.81",
},
"exodus": {
    "ip": "192.168.1.82",
},

All parameters are included in the ansible inventory as host variables.

The services output assigns machines to DNS names which are the same prefixes used as the ansible inventory group.

"cfg01": "domino",
"mon01": "blast",
"mon02": "exodus",

I recommend using these with a terraform DNS provider to automatically manage DNS for you.

Ansible inventory

This assumes you have a repository setup with multiple terraform environments for dev and prod. Each environment has an inventory config file e.g. hosts/prod/inventory.yaml

From ansible.cfg this is an example with a default prod inventory:

[defaults]
inventory_plugins = /path/to/python/site-packages
inventory = hosts/prod/inventory.yaml

You can install hostdb with pip install hostdb and find out the path to site-packages that it is installed under with with pip show hostdb.

These are examples of the prod and dev inventory config files. From hosts/prod/inventory.yaml:

---
plugin: hostdb.inventory
env: prod

From hosts/dev/inventory.yaml:

---
plugin: hostdb.inventory
env: dev

You can then use the service prefixes as inventory groups e.g. cfg or mon in the above examples.

Development

$ python3 -m venv venv
$ source venv/bin/activate
$ pip3 install -r requirements.txt