S3Client throws SdkClientException (Unable to load region) even when an SdkPlugin sets a region

[Techno3d]

Describe the bug

When building an S3Client, the client throws an SdkClientException because it was unable to load a region. However, I added an SdkPlugin to the builder which sets a region. I think this is due to the plugin being evaluated after the builder checks for a region.

Regression Issue

• Select this option if this issue appears to be a regression.

Expected Behavior

The plugin should be able to set the region, and the S3Client should build without throwing an exception.

Current Behavior

When an S3Client builds, it throws an SdkClientException due to not finding a region, even though the Plugin sets a region.

Error log:

Exception in thread "main" software.amazon.awssdk.core.exception.SdkClientException: Unable to load region from any of the providers in the chain software.amazon.awssdk.regions.providers.DefaultAwsRegionProviderChain@60f00693: [software.amazon.awssdk.regions.providers.SystemSettingsRegionProvider@65c7a252: Unable to load region from system settings. Region must be specified either via environment variable (AWS_REGION) or  system property (aws.region)., software.amazon.awssdk.regions.providers.AwsProfileRegionProvider@1e0b4072: No region provided in profile: default, software.amazon.awssdk.regions.providers.InstanceProfileRegionProvider@50378a4: Unable to contact EC2 metadata service.]
        at software.amazon.awssdk.core.exception.SdkClientException$BuilderImpl.build(SdkClientException.java:130)
        at software.amazon.awssdk.regions.providers.AwsRegionProviderChain.getRegion(AwsRegionProviderChain.java:70)
        at software.amazon.awssdk.awscore.client.builder.AwsDefaultClientBuilder.resolveRegion(AwsDefaultClientBuilder.java:375)
        at software.amazon.awssdk.utils.AttributeMap$DerivedValue.primeCache(AttributeMap.java:604)
        at software.amazon.awssdk.utils.AttributeMap$DerivedValue.get(AttributeMap.java:593)
        at software.amazon.awssdk.utils.AttributeMap$Builder.resolveValue(AttributeMap.java:400)
        at software.amazon.awssdk.utils.AttributeMap$Builder.internalGet(AttributeMap.java:389)
        at software.amazon.awssdk.utils.AttributeMap$Builder.access$1300(AttributeMap.java:201)
        at software.amazon.awssdk.utils.AttributeMap$Builder$1.get(AttributeMap.java:403)
        at software.amazon.awssdk.services.s3.DefaultS3BaseClientBuilder.lambda$finalizeServiceConfiguration$2(DefaultS3BaseClientBuilder.java:222)
        at software.amazon.awssdk.utils.AttributeMap$DerivedValue.primeCache(AttributeMap.java:604)
        at software.amazon.awssdk.utils.AttributeMap$DerivedValue.get(AttributeMap.java:593)
        at software.amazon.awssdk.utils.AttributeMap$Builder.resolveValue(AttributeMap.java:400)
        at software.amazon.awssdk.utils.AttributeMap$Builder.internalComputeIfAbsent(AttributeMap.java:331)
        at software.amazon.awssdk.utils.AttributeMap$Builder.putLazyIfAbsent(AttributeMap.java:275)
        at software.amazon.awssdk.core.client.config.SdkClientConfiguration$Builder.lazyOptionIfAbsent(SdkClientConfiguration.java:182)
        at software.amazon.awssdk.awscore.client.builder.AwsDefaultClientBuilder.finalizeAwsConfiguration(AwsDefaultClientBuilder.java:191)
        at software.amazon.awssdk.awscore.client.builder.AwsDefaultClientBuilder.finalizeChildConfiguration(AwsDefaultClientBuilder.java:173)
        at software.amazon.awssdk.core.client.builder.SdkDefaultClientBuilder.syncClientConfiguration(SdkDefaultClientBuilder.java:206)
        at software.amazon.awssdk.services.s3.DefaultS3ClientBuilder.buildClient(DefaultS3ClientBuilder.java:37)
        at software.amazon.awssdk.services.s3.DefaultS3ClientBuilder.buildClient(DefaultS3ClientBuilder.java:26)
        at software.amazon.awssdk.core.client.builder.SdkDefaultClientBuilder.build(SdkDefaultClientBuilder.java:173)
        at org.example.App.main(App.java:16)

Reproduction Steps

package org.example;

import java.net.URI;

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.S3ServiceClientConfiguration;

public class App {
    public static void main(String[] args) {
        S3Client client = S3Client.builder()
            .addPlugin(config -> {
                ((S3ServiceClientConfiguration.Builder) config)
                    .region(Region.US_EAST_1);
            })
            .build();
    }
}

Possible Solution

I think that the builder is reading the region before running plugins, which causes the exception to be thrown.

Additional Information/Context

No response

AWS Java SDK version used

software.amazon.awssdk:s3:2.47.4

JDK version used

openjdk 26.0.1 2026-04-21 OpenJDK Runtime Environment Temurin-26.0.1+8 (build 26.0.1+8) OpenJDK 64-Bit Server VM Temurin-26.0.1+8 (build 26.0.1+8, mixed mode, sharing)

Operating System and version

Microsoft Windows 11 Enterprise 10.0.26100 Build 26100

[Techno3d]

I may have accidentally checked the regression checkbox. I do not this is a regression, my bad.

[bhoradc]

@Techno3d - Noted, thanks for reporting this.

Your analysis appears to be correct, the SDK resolves region during client finalization, which occurs before plugins are invoked. Since no region is available through the builder or the default provider chain at that point, the build fails before your plugin gets a chance to set it.

Note that plugins do currently override region if it's already resolvable, so the plugin mechanism itself works, it's just that the SDK needs a value to be present before plugins execute.

In the meantime, you can work around this by setting region outside of the SdkPlugin. I will review this with the team to determine next steps. Thanks!