AWS Developer Blog

Version 2 Resource Interfaces

by Trevor Rowe | on | in Ruby | Permalink | Comments |  Share

In version 1 of the AWS SDK for Ruby provides a 1-to-1 client class for each AWS service. For many services it also provides a resource-oriented interface. These resource objects use the client to provide a more natural object-oriented experience when working with AWS APIs.

We are busy working resource interfaces for the v2 Ruby SDK.

Resource Interfaces

The following examples use version 1 of the aws-sdk gem. This first example uses the 1-to-1 client to terminate running instances:

ec2 = AWS::EC2::Client.new
resp = ec2.describe_instances
resp[:reservations].each do |reservation|
  reservation[:instances].each do |instance|
    if instance[:state][:name] == 'running'
      ec2.terminate_instances(instance_ids:[instance[:instance_id]])
    end
  end
end

This example uses the resource abstraction to start instances in the stopped state:

ec2 = AWS::EC2.new
ec2.instances.each do |instance|
  instance.start if instance.status == :stopped
end

Resources for Version 2

We have a lot of lessons learned from our v1 resource interfaces. We are busy working on the v2 abstraction. Here are some of the major changes from v1 to v2.

Memoization Interfaces Removed

The version 1 resource abstraction was very chatty by default. It did not memoize any resource attributes and a user could unknowingly trigger a large number of API requests. As a workaround, users could use memoization blocks around sections of their code.

In version 2, all resources objects will hold onto their data/state until you explicitly call a method to reload the resource. We are working hard to make it very obvious when calling a method on a resource object will generate an API request over the network.

Less Hand-Written Code and More API Coverage

The version 1 SDK has hand-coded resource and collection classes. In version 2, our goal is to extend the service API descriptions that power our clients with resource definitions. These definitions will be consumed to generate our resource classes.

Using resource definitions helps eliminate a significant amount of hand written code, ensures interfaces are consistent, and makes it easier for users to contribute resource abstractions.

We also plan to provide extension points to resources to allow for custom logic and more powerful helpers.

Resource Waiters

It is a common pattern to operate on a resource and then wait for the change to take effect. Waiting typically requires making an API request, asserting some value has changed and optionally waiting and trying again. Waiting for a resource to enter a certain state can be tricky. You need to deal with terminal cases, failures, transient errors, etc.

Our goal is to provide waiter definitions and attach them to our resource interfaces. For example:

# create a new table in Amazon DynamoDB
table = dynamodb.table('my-table')
table.update(provisioned_throughput: { 
  read_capcity_units: 1000
})

# wait for the table to be ready
table.wait_for(:status, 'ACTIVE')

In a follow up blog post, I will be introducing the resources branch of the SDK that is available today on GitHub. Please take a look and feedback is always welcome!