Bug: Regression error in v2 AppConfig parameters

[chrisclayson]

Expected Behaviour

If AppConfig returns an empty response (indicating that there have been no changes to the config since the last call to GetLatestConfiguration), then the provider should continue to return the cached version of the config.

Current Behaviour

As per the issue raised on v1 of the app, v2 is not correctly handling the empty response.

If an empty response is retrieved from AppConfig then null is returned which causes any transformer or, ultimately, the calling code to fail.

It seems the PR that was raised to fix the problem in v1 was not migrated to v2.

Code snippet

var provider = AppConfigProvider.builder()
                        .withClient(appConfigDataClient)
                        .withEnvironment(environmentVariables.getAppConfigEnvironment())
                        .withApplication(environmentVariables.getAppConfigApplication())
                        .build();

...

// Works fine on first call, but subsequent calls return `null`
var config = provider
    provider
        .withMaxAge(getConfigurationCacheTtl(), ChronoUnit.SECONDS)
        .withTransformation(ConfigTransformer.class)
        .get("test", Config.class);

Possible Solution

See PR #1673

Steps to Reproduce

• Setup a freeform configuration profile in AppConfig with some value (we used a JSON object { "version": 1 })
• Retrieve from a lambda using PowerTools parameters:

          var config = ParamManager.getAppConfigProvider("test", "test")
                .withMaxAge(30, ChronoUnit.SECONDS)
                .get("test");

• Fire continuous traffic at the lambda

The first retrieval, on any given runtime environment, will work fine, but after the 30 second TTL the next retrieve from AppConfg returns an empty string, which is returned from the get() method rather than original (cached value).

Powertools for AWS Lambda (Java) version

2.2.0 (latest)

AWS Lambda function runtime

Java 17

Debugging logs

[phipag]

Hey @chrisclayson,

thanks for reporting this bug. You are right, it appears the code slipped migration when refactoring the parameters module into sub-modules. I see the same problem when running in my AWS account.

We need to re-introduce the changes from PR #1673 again in this code snippet:

powertools-lambda-java/powertools-parameters/powertools-parameters-appconfig/src/main/java/software/amazon/lambda/powertools/parameters/appconfig/AppConfigProvider.java

Lines 96 to 109 in 3fa2b45

	// Get the value of the key. Note that AppConfig will return null if the value
	// has not changed since we last asked for it in this session - in this case
	// we return the value we stashed at last request.
	String value = response.configuration() != null ?
	response.configuration().asUtf8String() : // if we have a new value, use it
	establishedSession != null ?
	establishedSession.lastConfigurationValue :
	// if we don't but we have a previous value, use that
	null; // otherwise we've got no value
	// Update the cache so we can get the next value later
	establishedSessions.put(key, new EstablishedSession(nextSessionToken, value));
	return value;

Would you like to send a PR again @chrisclayson? Otherwise, I am happy to do it in time before our next minor version release tomorrow. We make a new minor release tomorrow before noon CEST. If we want to include it there, the PR should be sent some time tomorrow morning CEST.

[phipag]

Created PR: #1982