If you’re a savvy follower or reader of software development blogs and news, you might have come across the term idempotency at one point. If not, we are glad to be the ones introducing it to you. Most probably, you don’t have a clue what it is all about. In this write-up, we look at what is idempotency is and why it is important in web API design.
What is the meaning of idempotency?
In a nutshell, idempotency is the property that ensures that the results from an operation are the same, even if the same function is applied multiple times beyond the initial application. An idempotent operation produces the same results even when done once, twice, or a thousand times.
In the context of software development, idempotency plays a crucial role, especially when you are working with APIs. We all understand that APIs work – they allow the interaction between application and web services through sending requests and receiving responses. When a function is said to be idempotent in programming, it means that you can call it several times with the same request, but the results won’t change beyond the response delivered when the initial call was made. It means that even if multiple requests are completed successfully, the results will be independent, no matter how many times it was executed.
Idempotency with HTTP Methods
Several methods are used to make an API request. When a method is said to be idempotent, it guarantees a similar result when you send an identical request multiple times. However, in software development and programming, not all HTTP methods use idempotency.
The PUT method is often used when updating the resource state on a server. Invoking a PUT request will see the resource on the server updated with the request. This means that other subsequent calls won’t change anything, since they’ll just overwrite the resource state every time a similar request is made. This is why HTTP PUT is said to be idempotent.
The POST method is used when creating a new resource on a server. When you make the same POST requests multiple times, it will create new resources equaling the number of times you made the request. This is why POST is said not to be idempotent.
HTTP HEAD, GET, TRACE and OPTIONS
HEAD, GET, TRACE, and OPTIONS are idempotent. This is because the methods are primarily used to retrieve the resource representation or information at a given time. As such, even if you make multiple requests using HEAD, GET, TRACE, and OPTIONS methods, they’ll never change the resource state on the server.
While DELETE is said to be idempotent, there is a caveat. A successful DELETE request returns a 200 (meaning OK) or 204 (meaning no content). However, any subsequent calls will return 404 (meaning not found). While the first attempt may delete the target resource, a subsequent request will not alter the server’s resource status.
Why is Idempotency Essential?
The idempotency function is vitally essential since it helps improve safety and security by making APIs fault-tolerant and robust. Clients or application users may make several similar requests either by mistake or intentionally. If you optimize your API with the idempotency function, it guarantees that clients won’t get different results when making identical calls multiple times.
Idempotency also helps to minimize the resource state. Since identical requests don’t require any contextual form to be reserved in on the server, there is an improvement in performance as the server load caused by data retention is minimized.
Lastly, idempotency ensures that there is consistency between systems. When identical requests are made, they deliver a similar result. This guarantees alignment between systems, making it easy to trace and audit, thereby reduce reconciliation problems.
There is no doubt that idempotency is something that should be leveraged in every front to build better systems and applications. It boasts intuitive functions that can protect us from errors that are brought about by repetition. For instance, when used in payment systems, idempotency can minimize the incidences of sending or withdrawing money several times when you make multiple requests.