During some recent performance testing at work, we noticed an endpoint showing slower than usual response times. Digging into the calls, we found that on slow responses, virtually all the time was spent on waiting for a specific lambda function to return data. Digging into that function we found several calls that appeared to be timing out, and many others that were taking 9-10 seconds. This lead to a day or 2 spent reading up on the workings of AWS lambdas and how they work with Java. What was probably most striking is that while the solution to our problem was eventually findable with some Googling – and the “fix” involved practices that are mentioned in the official AWS documentation – they’re almost mentioned in passing, and don’t call out the performance impacts they have on your billed runtime.