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Fixing Load Balancing shuffle #48274

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Fixing Load Balancing shuffle #48274

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8947dae
Fixing Load Balancing shuffle
mrm9084 Mar 5, 2026
f9b17cc
Update ConnectionManager.java
mrm9084 Mar 6, 2026
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12 changes: 10 additions & 2 deletions ...g/cloud/appconfiguration/config/implementation/AppConfigurationReplicaClientsBuilder.java
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
import java.net.URL;
import java.time.Duration;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.function.Function;
import java.util.regex.Matcher;
Expand Down Expand Up @@ -156,7 +157,8 @@ List<AppConfigurationReplicaClient> buildClients(ConfigStore configStore) {
LOGGER.debug("Connecting to " + endpoint + " using Connecting String.");
ConfigurationClientBuilder builder = createBuilderInstance().connectionString(connectionString);

clients.add(modifyAndBuildClient(builder, endpoint, configStore.getEndpoint(), connectionStrings.size() - 1));
clients.add(
modifyAndBuildClient(builder, endpoint, configStore.getEndpoint(), connectionStrings.size() - 1));
}
} else {
DefaultAzureCredential defautAzureCredential = new DefaultAzureCredentialBuilder().build();
Expand All @@ -171,6 +173,11 @@ List<AppConfigurationReplicaClient> buildClients(ConfigStore configStore) {
clients.add(modifyAndBuildClient(builder, endpoint, configStore.getEndpoint(), endpoints.size() - 1));
}
}

if (configStore.isLoadBalancingEnabled()) {
Collections.shuffle(clients);
}

return clients;
}

Expand All @@ -196,7 +203,8 @@ AppConfigurationReplicaClient buildClient(String failoverEndpoint, ConfigStore c
}
}

private AppConfigurationReplicaClient modifyAndBuildClient(ConfigurationClientBuilder builder, String endpoint, String originEndpoint,
private AppConfigurationReplicaClient modifyAndBuildClient(ConfigurationClientBuilder builder, String endpoint,
String originEndpoint,
Integer replicaCount) {
TracingInfo tracingInfo = new TracingInfo(isKeyVaultConfigured, replicaCount,
Configuration.getGlobalConfiguration());
Expand Down
41 changes: 17 additions & 24 deletions ...java/com/azure/spring/cloud/appconfiguration/config/implementation/ConnectionManager.java
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Original file line number Diff line number Diff line change
Expand Up @@ -97,7 +97,7 @@ String getMainEndpoint() {
AppConfigurationReplicaClient getNextActiveClient(boolean useLastActive) {
if (useLastActive) {
List<AppConfigurationReplicaClient> clients = getAvailableClients();
for (AppConfigurationReplicaClient client: clients) {
for (AppConfigurationReplicaClient client : clients) {
if (client.getEndpoint().equals(lastActiveClient)) {
return client;
}
Expand All @@ -106,7 +106,7 @@ AppConfigurationReplicaClient getNextActiveClient(boolean useLastActive) {
if (activeClients.isEmpty()) {
lastActiveClient = "";
return null;
}
}

if (!configStore.isLoadBalancingEnabled()) {
if (!activeClients.isEmpty()) {
Expand All @@ -115,7 +115,8 @@ AppConfigurationReplicaClient getNextActiveClient(boolean useLastActive) {
return null;
}

// Remove the current client from the list. The list will be rebuilt and rotated on the next refresh cycle by findActiveClients().
// Remove the current client from the list. The list will be rebuilt and rotated on the next refresh cycle by
// findActiveClients().
AppConfigurationReplicaClient nextClient = activeClients.remove(0);
lastActiveClient = nextClient.getEndpoint();
return nextClient;
Expand All @@ -125,26 +126,18 @@ AppConfigurationReplicaClient getNextActiveClient(boolean useLastActive) {
* Finds the currently active clients for a given origin endpoint.
*/
void findActiveClients() {
activeClients = getAvailableClients();

if (!configStore.isLoadBalancingEnabled() || lastActiveClient.isEmpty()) {
return;
}

for (int i = 0; i < activeClients.size(); i++) {
AppConfigurationReplicaClient client = activeClients.get(i);
if (client.getEndpoint().equals(lastActiveClient)) {
int swapPoint = (i + 1) % activeClients.size();
List<AppConfigurationReplicaClient> rotatedClients = new ArrayList<>();

// Add elements from swapPoint to end
rotatedClients.addAll(activeClients.subList(swapPoint, activeClients.size()));

// Add elements from beginning to swapPoint
rotatedClients.addAll(activeClients.subList(0, swapPoint));

activeClients = rotatedClients;
return;
if (activeClients.size() == 0 && configStore.isLoadBalancingEnabled()) {
// If load balancing is enabled and there are no currently active clients, attempt to find any available
// clients
// Otherwise we continue from where we left off with the active clients list and rotate through.
activeClients = getAvailableClients();
} else if (!configStore.isLoadBalancingEnabled()) {
// If load balancing is not enabled, we want to ensure we are always using the most preferred available
// client. This means
// we check for available clients on each refresh and update the active clients list accordingly.
List<AppConfigurationReplicaClient> availableClients = getAvailableClients();
if (availableClients.size() > 0) {
activeClients = availableClients;
}
}
}
Expand Down Expand Up @@ -177,7 +170,7 @@ public List<AppConfigurationReplicaClient> getAvailableClients() {
}
}
} else if (configStore.isLoadBalancingEnabled()) {
for (AppConfigurationReplicaClient client: clients) {
for (AppConfigurationReplicaClient client : clients) {
if (client.getBackoffEndTime().isBefore(Instant.now())) {
availableClients.add(client);
}
Expand Down
72 changes: 72 additions & 0 deletions ...loud/appconfiguration/config/implementation/AppConfigurationReplicaClientBuilderTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -298,4 +298,76 @@ public void buildClientConnectionStringInvalid3Test() {
exception.getMessage());
}

@Test
public void buildClientsWithLoadBalancingEnabledTest() {
// Test that load balancing shuffles the order of clients
configStore = new ConfigStore();
List<String> endpoints = new ArrayList<>();

// Add multiple endpoints to shuffle
endpoints.add(TEST_ENDPOINT);
endpoints.add(TEST_ENDPOINT_GEO);
endpoints.add("https://third.test.config.io");
endpoints.add("https://fourth.test.config.io");

configStore.setEndpoints(endpoints);
configStore.setLoadBalancingEnabled(true);
configStore.validateAndInit();

clientBuilder = new AppConfigurationReplicaClientsBuilder(clientFactoryMock, null, false, false);
AppConfigurationReplicaClientsBuilder spy = Mockito.spy(clientBuilder);

ConfigurationClientBuilder builder = new ConfigurationClientBuilder();
when(builderMock.endpoint(Mockito.anyString())).thenReturn(builder);
when(builderMock.addPolicy(Mockito.any())).thenReturn(builderMock);
when(clientFactoryMock.build()).thenReturn(builderMock);

// Build clients multiple times and verify that order changes (due to shuffle)
List<AppConfigurationReplicaClient> clients1 = spy.buildClients(configStore);
List<AppConfigurationReplicaClient> clients2 = spy.buildClients(configStore);

assertEquals(4, clients1.size());
assertEquals(4, clients2.size());

// The order should potentially differ due to random shuffling
// We can't guarantee they're different, but we can verify the same endpoints exist
List<String> endpoints1 = clients1.stream().map(AppConfigurationReplicaClient::getEndpoint).toList();
List<String> endpoints2 = clients2.stream().map(AppConfigurationReplicaClient::getEndpoint).toList();

// All endpoints should be present in both lists (just potentially in different order)
assertTrue(endpoints1.containsAll(endpoints));
assertTrue(endpoints2.containsAll(endpoints));
}

@Test
public void buildClientsWithLoadBalancingDisabledTest() {
// Test that without load balancing, order is preserved
configStore = new ConfigStore();
List<String> endpoints = new ArrayList<>();

endpoints.add(TEST_ENDPOINT);
endpoints.add(TEST_ENDPOINT_GEO);
endpoints.add("https://third.test.config.io");

configStore.setEndpoints(endpoints);
configStore.setLoadBalancingEnabled(false);
configStore.validateAndInit();

clientBuilder = new AppConfigurationReplicaClientsBuilder(clientFactoryMock, null, false, false);
AppConfigurationReplicaClientsBuilder spy = Mockito.spy(clientBuilder);

ConfigurationClientBuilder builder = new ConfigurationClientBuilder();
when(builderMock.endpoint(Mockito.anyString())).thenReturn(builder);
when(builderMock.addPolicy(Mockito.any())).thenReturn(builderMock);
when(clientFactoryMock.build()).thenReturn(builderMock);

List<AppConfigurationReplicaClient> clients = spy.buildClients(configStore);

assertEquals(3, clients.size());
// When load balancing is disabled, order should match input order
assertEquals(TEST_ENDPOINT, clients.get(0).getEndpoint());
assertEquals(TEST_ENDPOINT_GEO, clients.get(1).getEndpoint());
assertEquals("https://third.test.config.io", clients.get(2).getEndpoint());
}

}