Q: Using Circuit Breaker in SAP Cloud SDK resilience - connectivity

Question

When I tried to use ResilienceDecorator.executeCallable() to enable circuit breaker, I have to throw out ResilienceRuntimeException in my callable to make the circuit break work. Sample code as below. Without it, circuit breaker is always closed. is this the right way to do it?
response = ResilienceDecorator.executeCallable(() -> {
HttpResponse response1 = tryHttpClient.get().execute(request);
if (response1.getStatusLine().getStatusCode() == 404){
throw new ResilienceRuntimeException("404 error is raised when calling SB api");
}
return response1;
},
ResilienceConfiguration.of(SubscriptionBillingAdapter.class).isolationMode(ResilienceIsolationMode.TENANT_OPTIONAL).timeLimiterConfiguration(ResilienceConfiguration.TimeLimiterConfiguration.of().timeoutDuration(Duration.ofSeconds(6L))).circuitBreakerConfiguration(ResilienceConfiguration.CircuitBreakerConfiguration.of().waitDuration(Duration.ofSeconds(600000L)).failureRateThreshold(1).closedBufferSize(1).halfOpenBufferSize(1)),
e -> {LOG.warn("resiliience fallback call: " + e); return response1;});
I am asking since I don't see any document of it. Also when I check how destination configuration in SCP is retrieved, I saw the following code in com.sap.cloud.sdk.cloudplatform.connectivity.DestinationService . It doesn't throw out ResilienceRuntimeException, when using ResilienceDecorator.executeCallable(). so my question is do I need to throw out ResilienceRuntimeException or not to make circuit breaker work? if I don't need, anything wrong in my code?
return (String)ResilienceDecorator.executeCallable(() -> {
XsuaaCredentials xsuaaCredentials = (new ServiceCredentialsRetriever()).getClientCredentials("destination");
AccessToken accessToken;
if (propagateUser) {
accessToken = xsuaaService.retrieveAccessTokenViaUserTokenExchange(xsuaaCredentials.getXsuaaUri(), xsuaaCredentials.getCredentials(), useProviderTenant);
} else {
accessToken = xsuaaService.retrieveAccessTokenViaClientCredentialsGrant(xsuaaCredentials.getXsuaaUri(), xsuaaCredentials.getCredentials(), useProviderTenant);
}
return this.fetchDestinationsJson(servicePath, accessToken);
}, ResilienceConfiguration.of(DestinationService.class).isolationMode(ResilienceIsolationMode.TENANT_OPTIONAL).timeLimiterConfiguration(TimeLimiterConfiguration.of().timeoutDuration(Duration.ofSeconds(6L))).circuitBreakerConfiguration(CircuitBreakerConfiguration.of().waitDuration(Duration.ofSeconds(6L))));

Answer 1

Steven
I'm not the most experienced in this specific part, but looking at your code it seems fine to me. When a server returns 404 Not found it's not an indication of a service failure or error, but that resource is simply not found. If in your case 404 means that an error took place and the request has to be retried with a resilient approach, you have to throw that exception to inform Resilience4J that smth went wrong.
While we're working on improving our documentation, I recommend you take a look at the existing tutorial explaining resilience within the SAP Cloud SDK context. There we also throw ResilienceRuntimeException for clarity:
public List<BusinessPartner> execute() {
return ResilienceDecorator.executeSupplier(this::run, myResilienceConfig, e -> {
logger.warn("Fallback called because of exception.", e);
return Collections.emptyList();
});
}
private List<BusinessPartner> run() {
try {
return businessPartnerService
.getAllBusinessPartner()
.select(BusinessPartner.BUSINESS_PARTNER,
BusinessPartner.LAST_NAME,
BusinessPartner.FIRST_NAME,
BusinessPartner.IS_MALE,
BusinessPartner.IS_FEMALE,
BusinessPartner.CREATION_DATE,
BusinessPartner.TO_BUSINESS_PARTNER_ADDRESS
.select(BusinessPartnerAddress.CITY_NAME,
BusinessPartnerAddress.COUNTRY,
BusinessPartnerAddress.TO_EMAIL_ADDRESS
.select(AddressEmailAddress.EMAIL_ADDRESS)
)
)
.filter(BusinessPartner.BUSINESS_PARTNER_CATEGORY.eq(CATEGORY_PERSON))
.orderBy(BusinessPartner.LAST_NAME, Order.ASC)
.top(200)
.execute(destination);
} catch (ODataException e) {
throw new ResilienceRuntimeException(e);
}
}
Regarding the code snippet from the DestinationService, I believe that fetchDestinationsJson() method throws an implicit exception thus letting Resilience4J know that smth went wrong. While in your case HttpClient won't throw anything when receiving 404 as it's a correct response code as any other.
I also think that checking CircuitsBreaker examples from Resilience4J library might be helpful.
I hope it helps:)

Answer 2

No you do not have to throw a ResilienceRuntimeException. In fact the SDK only uses that to wrap checked and unchecked exceptions into an unchecked exception which wraps all kinds of failures that occur within a resilient call.
Please expand your question with more details, I'll then expand this answer:
Which version of the SDK are you using?
How (and how often) do you invoke the decorated callable? Please expand the code block.
Please specify the exact behaviour you observe. What exception is thrown when you invoke the decorated callable? If the circuit breaker opens this should be a CallNotPermittedException wrapped inside a ResilienceRuntimeException
Reduce the callable to simply throw an exception in order to simplify the code
Reduce the resilience configuration to only use a circuit breaker (leverage ResilienceConfiguration.empty()). If that works add stuff back in again until it doesn't.
For reference also please find the documentation of resilience4j which the SDK uses under the hood to perform resilient operations.