At Instacart, we run our infrastructure on AWS, so our systems often deal withAWS ARNs. We often run into cluttered code, and needed to develop a solution for simpler, safer code. That’s why today, we’re releasing arn, a Python library that simplifies parsing, validating, and working with AWS ARNs in a type-safe way.

Here’s an example of what arncan do, in this case parsing a Target Group ARN:

from arn.elbv2 import TargetGroupArn

target_group_arn_str = (
    "arn:aws:elasticloadbalancing:us-east-1:123456789012:targetgroup/foo-bar/abc123"
)    
target_group_arn = TargetGroupArn(target_group_arn_str)

# use the ARN instance's __str__ to format the ARN back into a string
assert str(target_group_arn) == target_group_arn_str

# common attributes
assert target_group_arn.partition == "aws"
assert target_group_arn.service == "elasticloadbalancing"
assert target_group_arn.region == "us-east-1"
assert target_group_arn.account == "123456789012"

# attributes specific to the type of AWS resource
assert target_group_arn.name == "foo-bar"
assert target_group_arn.internal_id == "abc123"

arn also checks that its input is indeed a valid ARN:

If you’re using type annotations, arn can help you enforce that function parameters are valid ARNs:

If you have multiple resources in your AWS infrastructure that have some attributes in common, arn can also be used to generate an ARN from another:

What resources are supported?

arn is still quite new, so it only supports the AWS resource types that we use here at Instacart, plus a few more popular ones:

ECS

• Capacity provider
• Container Instance
• Cluster
• Service
• Task
• Task definition
• TaskSet

ELBv2

• Load Balancers (Application and Network)
• ALB/NLB Listeners
• ALB/NLB Listener Rules
• Target Group

IAM

• Role
• STS Assumed role

S3

• Access point
• Bucket
• Job
• Object

How do I get it?

arn supports Python 3.6 and up and has no runtime dependencies (except for a dataclasses backport if you’re on Python 3.6). To install it, simply run:

pip install arn

or add arn to your setup.pyor requirements.txt.

The docs are available at https://arn.readthedocs.io/en/latest/

I want to contribute

If you’re interested in contributing, or just want to take a look at the source, come visit us at https://github.com/instacart/arn.