AWS API Gateway GET response always cached

Question

Update: I figured it out, please see the answer post below.

I have an AWS API Gateway api defined with various resources and various GET and POST methods.

Everything works mostly fine. POSTs are going through. GETs return a response (JSON payload) except that the returned value seems to be a cached value.

My GET api calls a Lambda function that calls a query to RDS. I can confirm my responses are stale because:

• When I manually Query the RDS, I get the updated value
• I have Cloud Watch logs enabled and the lambda function does not get called (I believe I have it set up correctly because when I test invoke the lambda, I can get Cloud Watch logs)

It did refresh once, but I think that was because I crossed some (like 1hr) caching threshold or something.

I understand that API Gateway generates a CloudFront behind the scenes. And I feel that this is what is doing the caching. But that's just a guess and I have no proof. Maybe some kind of default caching TTL?

I obviously have caching turned off on my API Gateway stage. I even tried enabling it, setting the TTL to 1, flushing the cache, and disabling cache again. Each stage of that testing still returned the stale values.

I do not know if it is relevant, but additional details:

• I have CORS enabled ("*")
• I have Cognito authorizers enabled
• I pass in the JWT token via the Authorization header (this is all working fine)

Is there some header I'm supposed to pass to request an uncached value? I went to CloudFront, but here are no configurations there.

All other posts on API Gateway caching seem to be about caching not working or people asking about cache key specificity. I haven't seen anything about the value ALWAYS being cached no matter what. So I feel like I'm missing something obvious...

Any help or debugging tips would be much appreciated!

Answer 1

Ok, so I feel like an idiot for answering my own question but hopefully it helps someone one day.

This was not an API Gateway caching issue. The problem was a pymysql connection & lambda session caching issue.

My Lambda was using pymysql to query the MySQL RDS. Per recommended performance reasons, I reused the connection across lambdas (meaning I did not close the connection each time).

The solution was to call conn.commit()

after I did my fetchall()

What was happening was that my subsequent calls were returning a cached query result (termed a consistent read. Thanks! @Michael - sqlbot) I believe I probably had more than one lambda containers or something so when I was inactive for a while (ie busy reading stackoverflow posts), the lambda would unload. Then my next API gateway attempt would reinitialize a fresh lambda handler and a branch new connection would be created (without a cache). So this is why it seems to "sometimes work, then stop".

Apologies if I wasted anyone's time.