Astromech is a collection of utilities that I found myself copying all over my lambda functions and serverless projects. For the sake of DRYing up my code, I collected them in a single library.
Astromech implements lazy-initialization for Boto3 service clients:
For each service, there is a global client variable that gets reused between invocations of the labmda function
container. Code that want access to the client achieves this by using a client() function that initializes it
if necessary.
Code example:
from astromech import s3, dynamodb
s3.client().get_object(Bucket=..., Key=...)
dynamodb.table().get_item(Key=...)The service client initialization functions, look for the environment variable LOCALSTACK_[SERVICE]_URL
(for example, LOCALSTACK_S3_URL).
If it finds one, then it uses its value as the endpoint_url for the Boto3 client function.
All you have to do to run tests with LocalStack is to set these variables in your local environment. No changes to the code are necessary. Naturally, this works with any other downloadable version of AWS services, like DynamoDB local.
There are a few utility functions in each service. These usually save 2-3 lines of boilerplate code. Not a lot, but for very common functionality that is repeated all across the code base, it becomes worthwhile.
For example, to check if an object exists on S3, you have to send a head_object request and catch the exception
if it doesn't exist. With astromech.s3 you just call exists(bucket, key), much like you would do with a local
file.
In the Star Wars universe, astromech is a type of utility droid, the most famous of which (whom?) is R2-D2.
Read more on Wookiepedia.
