Smoother Cloud Resources: The Liskov Substitution Way

Continuing this SOLID series, where we strive to blend best practices with AWS, we have now reached the Liskov Substitution Principle, known for being one of the most complex. As we delve into its application in AWS resources, we aim to simplify its implementation, making it a powerful tool for creating interchangeable and resilient cloud components.

Definition

Like always, let's first understand what is the Liskov Substitution principle:

The Liskov Substitution Principle (LSP) is one of the SOLID principles of object-oriented programming, introduced by Barbara Liskov. It states that objects of a base class should be replaceable with objects of a derived class without affecting the correctness of the program. In simpler terms, if a program is using a base class, substituting it with any of its derived classes should not alter the desired behavior of the program. This principle ensures a consistent and predictable behavior of the code when using polymorphism and inheritance.

Sounds tricky right? Let's visualize this exact scenario:

You can see that Sam (The parent class) is supposed to serve coffee, but when he is not present, Eden (The child class) might not be able to make the same type of coffee as his father. However, he can make cappuccino (exhibiting specialized behavior), ensuring that even if the child class substitutes for the parent class, it won't break the expected functionality of serving coffee.

Okay, but how does this relate to AWS?

It's a valid question because the Liskov Substitution Principle (LSP) does not have a direct correlation as much as the Single Responsibility Principle or the Open-Closed Principle within the context of AWS. While LSP primarily focuses on object-oriented programming principles, its application in AWS resource management may not be as straightforward. However, the principles of consistency and adherence to expected behaviors remain crucial across various programming paradigms, including AWS architecture, which is what we are going to see next.

LSP and AWS

Resource Tagging and Metadata:

• Leverage AWS resource tagging and metadata to convey information about resource behavior.
• When substituting resources, verify that the tagging and metadata conventions align with expected behaviors to maintain consistency.

IAM Policies:

• Design IAM policies with a consistent approach to permissions.
• When substituting policies, ensure that the derived policy provides the necessary permissions without introducing unexpected access changes.

API Gateway and Lambda Functions:

• In API Gateway designs, maintain consistency in input and output formats.
• For Lambda functions, ensure that derived functions fulfill the same purpose or extend functionalities without altering expected inputs and outputs.

Error Handling:

• Implement consistent error-handling mechanisms across AWS resources.
• Derived resources should handle errors in a manner consistent with their base resources to ensure graceful degradation.

By adopting these practices, you promote the LSP's principles within your AWS architectures, fostering a design where substitutability of resources doesn't compromise the expected behaviors and consistency of your cloud solutions.

If you are interested in reading more articles about applying SOLID principles, you can click here.