Creating Cloud Resources Using Fog

What is fog?

Fog is a ruby cloud service library that provides a common abstraction over cloud provider SDKs. It supports a large number of cloud providers like AWS, Azure, GCP, DigialOcean, etc. albeit with varying degrees of maturity. You can find the whole list here. The documentation is lack-luster but most fog cloud provider libraries have extensive test suites that serve as a how-to for that particular provider.

Why fog?

So you might be asking yourself, “Doesn’t terraform do this for me?”.

Terraform at its heart a large diffing algorithm that maintains a snapshot of your infrastructure’s state and tries to make changes based on the current vs. desired state. It uses a configuration language developed by HashiCorp called hcl to create, update and manage that state.

Fog on the other hand is a ruby library that can be used like any other rubygem. It’s just ruby so you get all of the goodness of a dynamic, object-oriented programming language when creating cloud resources. Where fog really shines is as a cross-platform SDK that gives a consitent interface to doing common tasks like creating servers, volumes, etc. Another great feature is Fog.mock that lets you unit test your logic without creating any cloud resources and incurring costs.

Use Cases

I recently choose fog for a project where I needed to create a rails app that would allow users to CRUD compute resources and security groups for AWS, Azure and GCP.

Fog is a good choice if:

your team is already using ruby and you’re tasked with creating and managing your own compute and storage infrastructure.
you want loops, branching logic (if-else), OOP design patterns, mock testing using rspec or minitest
you need to use more than one cloud-provider sdk and want a common interface across compute and storage resources.

Example

In the example script below I’m using fog to create one ec2 instance. Once the instance is created, the instance’s ID is saved to a yaml file to make things idempotent.

# frozen_string_literal: true

require 'fog/aws'
require 'yaml/store'

STORE = YAML::Store.new 'fog-aws.yml'
instance_id = STORE.transaction { STORE['instance_id'] }
ec2 = Fog::Compute.new(provider: 'AWS', region: 'us-east-1')

if instance_id.nil?
  key_name = 'fog-test'
  ec2.key_pairs.create(name: key_name) if ec2.key_pairs.get(key_name).nil?
  
  instance = ec2.servers.create(
    tags: { Name: 'fog-ec2' },
    key_name: key_name,
    flavor_id: 't3.small',
    image_id: 'ami-087c17d1fe0178315'
  )
  puts 'Instance is creating'
  STORE.transaction { STORE['instance_id'] = instance.id }
  instance.wait_for { ready? }
  puts 'Instance is ready!'
else
  puts 'Instance already exists'
  instance = ec2.servers.get(instance_id)
end

puts <<-EOF
public_dns_name = http://#{instance.dns_name}
public_ip_address = http://#{instance.public_ip_address}
private_dns_name = http://#{instance.private_dns_name}
private_ip_address = http://#{instance.private_ip_address}
EOF