How to deal with load tests on APIs that make costly external calls?

Grafana k6
1

Hello, I’m currently trying to understand the correct approach of using Grafana k6 to load test an API route that internally makes other API calls to services that costs $$.

I have a simple use case that could help the community to understand my problem:

I want to load test a route POST /forgot-password
This route is very simple, it receives as body input the e-mail address of a user, and returns 204.
Internally, the code that handles this makes two operations:

  1. Make a database call to search for a user with this e-mail address
  2. In case the user is found, it makes a external call to another API (send-email) that sends an e-mail to the e-mail address sent as input to the route. (This costs $$)

I want to use Grafana k6 to load test this forgot-password API, but I want step 2 to be mocked, since I don’t want to send real e-mails calling the external service.

I thought about a solution, I would like to know what the Grafana k6 community thinks about it:

  • I’ll update the code that handles the forgot-password endpoint, and I’ll create a mock of the send-email API call.
  • I’ll make the code read the k6 tags sent when calls are made using Grafana k6 tool (HTTP Requests | Grafana k6 documentation), if the code detects these tags as input, I’ll inject the mock version of the send-email API call, otherwise the code will continue to work as expected (making the real call that costs $$)

It this the correct approach when dealing with load tests with APIs that makes costly external calls?

2

Yes, but make sure you add the correct latency(latency of the real service) to the mock you created.

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