The cloud journey

Debugging when you dont know where to start

Programming has lots of challenges along the road, and one of the big ones is when your program does something you didn't want. This can even be harder if there isn't a good way to understand what it was supposed to do, espescially if its an API or 3rd party library that isn't well documented.

While I like AWS, some things are harder than they seem. Obe of them is Lambda, the main serverless piece in the AWS ecosystem. Seemingly a request/responae system, it doesn't seem like you can debug it inline; but you can.

In AWS, the way logs are handled are through a tool called logwatch. For Lambda, any bits printed to STDOUT are written in the logwatch area. The issue is if you aren't familiar with AWS tooling, you may not know that it exists, and even if you do you may not know how to access the info.

I had this issue with my early Python Lambdas. Something would go wrong, and I'd read the errors like tea leaves and try to understand what had failed, making changes in the dark without understanding. It was painful and slow, and incredibly frustrating.

When I discovered where logwatch was hiding and understood it snags regular prints, rathen than using gueeses and hope I could print my variables and see, oh, this doesn't have the value I expect and sometimes had no value at all.

Its like a superpowwr, and streamlines things a bunch.

I have one other annoyance, and that is with AWS docs. The docs are long ans detailed, but often lack examples or have a single one. I don't expect hundreds, but it would be nice to see what is being passed to most of the parameters, to know I'm in the vicinity of what should work.

So, here is a short guide on how to figure this out.

First, don't assume anything, and by this I mean until you rule something out, the issue could be anywhere. What you want to do is narrow down the scope to the smallest subset that still shows the issue - what are the inputs, how is it invoked, what are the outputs supposed to be?

Next, what is the path through the code you think should be taken, given the invocation and inputs? Reason this out from reading the code, as it can help spot oddness. At this point we want to debug, so run it through a debugger, or add print statements. I like prints in stuff like web interactions, as it can be a bit quicker, but this is personal preference.

We're looking for something off. Is what we're passing to a function right? Is the return right? Is formatting and filtering good?

Finally, change one thing at a time. Even though it might feel like you should clean things up in general, you want to fix the bug -- so focus on that. Isolate, confirm the issue, change, confirm the fix. That is the way forward.

I might post a walkthrough in the future -- stay tuned!

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By CloudSec9

In aws.

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By CloudSec9

In aws.

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By CloudSec9

In aws.

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By CloudSec9

In aws.

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By CloudSec9

In aws.

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Published: Wed 23 November 2022
By CloudSec9

In aws.

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Published: Sun 06 November 2022
By CloudSec9

In aws.

Learning a new technology is fun. The cursing, the reading, the questioning why nothing ever works and why article writers have it in for you. Fun fun. Oh, and sometimes certain things work and you actually gain a bit of skill.

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By CloudSec9

In aws.

So, I've started to port over my pages from my current dynamic but unthemed system to a Jamstack version, and that is going well. What isn't going as well is getting the files from the generated directories onto the real system in an easy way. Unlike in the past, I've …
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Published: Sun 20 June 2021
By CloudSec9

In aws.

At month's end, I'll be losing the free t4 trial and need to offload some of that stuff elsewhere. I also want to clean up some older snapshots and AMIs that I have, as well as delete some of the S3 buckets I created doing the SysOps Admin labs. I …
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