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S3Mock

S3Mock is a lightweight server that implements a subset of the Amazon S3 API for local integration testing. It removes the need for real AWS infrastructure during development and testing.

Recommended usage: Run S3Mock as a Docker container or via Testcontainers to avoid classpath conflicts.

Quick Start

Get up and running in 30 seconds:

# 1. Start S3Mock
docker run -p 9090:9090 adobe/s3mock

# 2. Create a bucket
aws s3api create-bucket --bucket my-bucket --endpoint-url http://localhost:9090

# 3. Upload a file
aws s3api put-object --bucket my-bucket --key my-file --body ./my-file --endpoint-url http://localhost:9090

# 4. Download the file
aws s3api get-object --bucket my-bucket --key my-file --endpoint-url http://localhost:9090 output-file

For programmatic testing, see Testcontainers or JUnit 5 Extension below.

Changelog

Version Compatibility

S3Mock Status Spring Boot Kotlin Java (target) Java (compile) AWS SDK v2 Testcontainers
5.x Active 4.0.x 2.3 17 25 2.x 2.x
4.x Deprecated 3.x 2.1-2.2 17 17 2.x 1.x
3.x End of Life 2.x 1.x-2.0 17 17 2.x 1.x
2.x End of Life 2.x - 11 11 1.x/2.x -
1.x End of Life 2.x - 11 11 1.x/2.x -

Migration Guides

4.x to 5.x (Current)

  • Filesystem changes: The internal file structure changed; existing data may be incompatible with the new version.
  • Jackson 3: XML annotations migrated to Jackson 3 (tools.jackson packages)
  • AWS SDK v1 removed: All v1 client support dropped
  • JUnit 4 removed: The s3mock-junit4 module has been removed
  • Controller package moved: com.adobe.testing.s3mock → com.adobe.testing.s3mock.controller
  • Legacy environment variables removed: Replaced by new environment variables — see Configuration.
  • Legacy properties removed: Replaced by new configuration properties — see Configuration.
  • Apache Commons removed: commons-compress, commons-codec, commons-lang3 replaced by Kotlin/Java stdlib
  • Owner DisplayName removed: AWS APIs no longer return DisplayName — this is a breaking change for persisted data

3.x to 4.x

  • Tomcat replaces Jetty: Embedded container switched from Jetty to Tomcat
  • Versioning API: Basic S3 versioning support added
  • If-(Un)modified-Since: Conditional request handling added

For full details, see the Changelog.

Supported S3 Operations

See the complete operations table in the AWS documentation.

Click to expand operations table (operations marked ✅ are supported)
Operation Support Comment
AbortMultipartUpload ✅
CompleteMultipartUpload ✅
CopyObject ✅
CreateBucket ✅
CreateMultipartUpload ✅
DeleteBucket ✅
DeleteBucketAnalyticsConfiguration ❌
DeleteBucketCors ❌
DeleteBucketEncryption ❌
DeleteBucketIntelligentTieringConfiguration ❌
DeleteBucketInventoryConfiguration ❌
DeleteBucketLifecycle ✅
DeleteBucketMetricsConfiguration ❌
DeleteBucketOwnershipControls ❌
DeleteBucketPolicy ❌
DeleteBucketReplication ❌
DeleteBucketTagging ❌
DeleteBucketWebsite ❌
DeleteObject ✅
DeleteObjects ✅
DeleteObjectTagging ✅
DeletePublicAccessBlock ❌
GetBucketAccelerateConfiguration ❌
GetBucketAcl ❌
GetBucketAnalyticsConfiguration ❌
GetBucketCors ❌
GetBucketEncryption ❌
GetBucketIntelligentTieringConfiguration ❌
GetBucketInventoryConfiguration ❌
GetBucketLifecycle ❌ Deprecated in S3 API
GetBucketLifecycleConfiguration ✅
GetBucketLocation ✅
GetBucketLogging ❌
GetBucketMetricsConfiguration ❌
GetBucketNotification ❌
GetBucketNotificationConfiguration ❌
GetBucketOwnershipControls ❌
GetBucketPolicy ❌
GetBucketPolicyStatus ❌
GetBucketReplication ❌
GetBucketRequestPayment ❌
GetBucketTagging ❌
GetBucketVersioning ✅
GetBucketWebsite ❌
GetObject ✅
GetObjectAcl ✅
GetObjectAttributes ✅ for objects, not parts
GetObjectLegalHold ✅
GetObjectLockConfiguration ✅
GetObjectRetention ✅
GetObjectTagging ✅
GetObjectTorrent ❌
GetPublicAccessBlock ❌
HeadBucket ✅
HeadObject ✅
ListBucketAnalyticsConfigurations ❌
ListBucketIntelligentTieringConfigurations ❌
ListBucketInventoryConfigurations ❌
ListBucketMetricsConfigurations ❌
ListBuckets ✅
ListMultipartUploads ✅
ListObjects ✅ Deprecated in S3 API
ListObjectsV2 ✅
ListObjectVersions ✅
ListParts ✅
PostObject ✅
PutBucketAccelerateConfiguration ❌
PutBucketAcl ❌
PutBucketAnalyticsConfiguration ❌
PutBucketCors ❌
PutBucketEncryption ❌
PutBucketIntelligentTieringConfiguration ❌
PutBucketInventoryConfiguration ❌
PutBucketLifecycle ❌ Deprecated in S3 API
PutBucketLifecycleConfiguration ✅
PutBucketLogging ❌
PutBucketMetricsConfiguration ❌
PutBucketNotification ❌
PutBucketNotificationConfiguration ❌
PutBucketOwnershipControls ❌
PutBucketPolicy ❌
PutBucketReplication ❌
PutBucketRequestPayment ❌
PutBucketTagging ❌
PutBucketVersioning ✅
PutBucketWebsite ❌
PutObject ✅
PutObjectAcl ✅
PutObjectLegalHold ✅
PutObjectLockConfiguration ✅
PutObjectRetention ✅
PutObjectTagging ✅
PutPublicAccessBlock ❌
RestoreObject ❌
SelectObjectContent ❌
UploadPart ✅
UploadPartCopy ✅
WriteGetObjectResponse ❌

Usage

Docker (Recommended)

Available on Docker Hub, the Docker image is the recommended way to run S3Mock.

Basic usage:

docker run -p 9090:9090 -p 9191:9191 adobe/s3mock

Ports: 9090 (HTTP), 9191 (HTTPS)

With configuration:

docker run -p 9090:9090 -p 9191:9191 \
  -e COM_ADOBE_TESTING_S3MOCK_STORE_INITIAL_BUCKETS=test-bucket \
  -e SPRING_PROFILES_ACTIVE=debug \
  adobe/s3mock

Docker Compose:

services:
  s3mock:
    image: adobe/s3mock:latest
    environment:
      - COM_ADOBE_TESTING_S3MOCK_STORE_INITIAL_BUCKETS=bucket1,bucket2
    ports:
      - 9090:9090
      - 9191:9191

With persistent storage:

services:
  s3mock:
    image: adobe/s3mock:latest
    environment:
      - COM_ADOBE_TESTING_S3MOCK_STORE_ROOT=containers3root
      - COM_ADOBE_TESTING_S3MOCK_STORE_RETAIN_FILES_ON_EXIT=true
    ports:
      - 9090:9090
    volumes:
      - ./locals3root:/containers3root

Testcontainers

The S3MockContainer provides a ready-to-use Testcontainers implementation.

Maven dependency:

<dependency>
  <groupId>com.adobe.testing</groupId>
  <artifactId>s3mock-testcontainers</artifactId>
  <version>...</version>
  <scope>test</scope>
</dependency>

Usage example:

@Testcontainers
class MyTest {
  @Container
  val s3Mock = S3MockContainer("latest")
    .withInitialBuckets("test-bucket")

  @Test
  fun test() {
    val s3Client = S3Client.builder()
      .endpointOverride(URI.create(s3Mock.httpEndpoint))
      .region(Region.US_EAST_1)
      .credentialsProvider(StaticCredentialsProvider.create(
        AwsBasicCredentials.create("foo", "bar")
      ))
      .build()

    s3Client.createBucket { it.bucket("my-bucket") }
  }
}

JUnit 5 Extension

Note: This module may be removed in S3Mock 6.x. Consider using Testcontainers instead.

Maven dependency:

<dependency>
  <groupId>com.adobe.testing</groupId>
  <artifactId>s3mock-junit5</artifactId>
  <version>...</version>
  <scope>test</scope>
</dependency>

Usage:

@ExtendWith(S3MockExtension::class)
class MyTest {
  @Test
  fun test(s3Client: S3Client) {
    s3Client.createBucket { it.bucket("test-bucket") }
  }
}

See examples: Declarative | Programmatic

TestNG Listener

Note: This module may be removed in S3Mock 6.x. Consider using Testcontainers instead.

Maven dependency:

<dependency>
  <groupId>com.adobe.testing</groupId>
  <artifactId>s3mock-testng</artifactId>
  <version>...</version>
  <scope>test</scope>
</dependency>

Configure in testng.xml - see example configuration.

AWS CLI

Pass --endpoint-url to point the CLI at S3Mock, and add --no-verify-ssl for HTTPS:

# Create bucket
aws s3api create-bucket --bucket my-bucket --endpoint-url http://localhost:9090

# Upload object
aws s3api put-object --bucket my-bucket --key my-file --body ./my-file --endpoint-url http://localhost:9090

# Download object
aws s3api get-object --bucket my-bucket --key my-file --endpoint-url http://localhost:9090 output-file

# HTTPS
aws s3api get-object --bucket my-bucket --key my-file --no-verify-ssl --endpoint-url https://localhost:9191 output-file

cURL

# Create bucket
curl -X PUT http://localhost:9090/my-bucket/

# Upload object
curl -X PUT --upload-file ./my-file http://localhost:9090/my-bucket/my-file

# Download object
curl http://localhost:9090/my-bucket/my-file -O

# HTTPS (with self-signed certificate)
curl --insecure https://localhost:9191/my-bucket/my-file -O

Configuration

Configure S3Mock using environment variables:

Variable Default Description
COM_ADOBE_TESTING_S3MOCK_STORE_ROOT Java temp directory Base directory for file storage
COM_ADOBE_TESTING_S3MOCK_STORE_REGION us-east-1 AWS region to mock
COM_ADOBE_TESTING_S3MOCK_STORE_INITIAL_BUCKETS none Comma-separated list of buckets to create on startup
COM_ADOBE_TESTING_S3MOCK_STORE_RETAIN_FILES_ON_EXIT false Keep files after shutdown
COM_ADOBE_TESTING_S3MOCK_STORE_VALID_KMS_KEYS none Comma-separated KMS key ARNs (validation only, no encryption)
COM_ADOBE_TESTING_S3MOCK_CONTROLLER_CONTEXT_PATH "" Base context path for all endpoints

Spring Profiles

Activate profiles via the SPRING_PROFILES_ACTIVE environment variable:

Profile Description
debug Debug-level logging for Spring Web, Apache, and request details. Also activates actuator.
trace Trace-level logging for Spring Web, Apache, and request details. Also activates actuator.
actuator Enables JMX and all Spring Boot Actuator endpoints (health, info, etc.).

Actuator endpoints are disabled by default. To enable them:

# Via debug or trace profile (also enables verbose logging)
docker run -p 9090:9090 -p 9191:9191 -e SPRING_PROFILES_ACTIVE=debug adobe/s3mock

# Via actuator profile only (no extra logging)
docker run -p 9090:9090 -p 9191:9191 -e SPRING_PROFILES_ACTIVE=actuator adobe/s3mock

# Via individual environment variables (without any profile)
docker run -p 9090:9090 -p 9191:9191 \
  -e MANAGEMENT_ENDPOINTS_ACCESS_DEFAULT=unrestricted \
  -e MANAGEMENT_ENDPOINTS_WEB_EXPOSURE_INCLUDE='*' \
  adobe/s3mock

Health Check

S3Mock exposes two readiness endpoints:

/favicon.ico (always available)

Returns HTTP 200 OK with an empty body. This endpoint is always active, requires no configuration, and is used by Testcontainers and the integration test suite to detect readiness:

curl -sf http://localhost:9090/favicon.ico

/actuator/health (requires actuator profile)

The standard Spring Boot health endpoint. Only available when the actuator profile (or debug/trace) is active:

# Start with actuator enabled
docker run -p 9090:9090 -p 9191:9191 -e SPRING_PROFILES_ACTIVE=actuator adobe/s3mock

# Check health
curl -sf http://localhost:9090/actuator/health

Docker Compose health check example:

services:
  s3mock:
    image: adobe/s3mock:latest
    ports:
      - 9090:9090
      - 9191:9191
    healthcheck:
      test: ["CMD", "wget", "--spider", "-q", "http://localhost:9090/favicon.ico"]
      interval: 5s
      retries: 3

Important Limitations

  • Path-style access only: S3Mock supports http://localhost:9090/bucket/key, not http://bucket.localhost:9090/key
  • Presigned URLs: Accepted but not validated (expiration, signature, HTTP verb not checked)
  • Self-signed SSL: The bundled certificate requires clients to trust it or disable SSL verification
  • KMS: Key ARNs are validated, but no actual encryption is performed
  • Not for production: S3Mock is a testing tool and lacks the security features required for production use

Troubleshooting

Click to expand troubleshooting guide

Port already in use (Address already in use)

  • Ports 9090 (HTTP) and 9191 (HTTPS) must be available
  • Check with: lsof -i :9090 (macOS/Linux) or netstat -ano | findstr :9090 (Windows)
  • Stop conflicting processes or map to different ports: docker run -p 9091:9090 adobe/s3mock

Connection refused

  • Verify S3Mock is running: docker ps | grep s3mock
  • Ensure you're using the correct endpoint URL (e.g., http://localhost:9090)
  • Wait for startup to complete — check with curl -sf http://localhost:9090/favicon.ico or check logs with docker logs <container-id>

SSL certificate errors

  • S3Mock uses a self-signed certificate on the HTTPS port (9191)
  • AWS CLI: Add --no-verify-ssl flag
  • cURL: Add --insecure flag
  • Java/Kotlin: Configure the SDK to trust the S3Mock certificate or disable SSL verification

Docker not running (Testcontainers)

  • Testcontainers and integration tests require a running Docker daemon
  • Start Docker Desktop or the Docker service before running tests
  • Check with: docker info

Classpath conflicts (JUnit 5 Extension / embedded mode)

  • S3Mock's embedded Spring Boot server may conflict with your application's dependencies
  • Recommended: Use Testcontainers or Docker instead to run S3Mock in isolation
  • If using embedded mode, ensure compatible Spring Boot versions

AWS SDK endpoint configuration

  • AWS SDK v2: Use .endpointOverride(URI.create("http://localhost:9090"))
  • Credentials: Supply any dummy credentials (e.g., AwsBasicCredentials.create("foo", "bar"))
  • Region: Specify any region (S3Mock defaults to us-east-1)

Objects not found / wrong bucket

  • S3Mock supports path-style access only: http://localhost:9090/bucket/key
  • Virtual-hosted style (http://bucket.localhost:9090/key) is not supported
  • Verify your SDK client is configured for path-style access

File System Structure

S3Mock stores data on disk with the following structure:

<root>/
  <bucket-name>/
    bucketMetadata.json              # Bucket metadata
    <object-uuid>/
      binaryData                     # Object content
      objectMetadata.json            # Object metadata
      <version-id>-binaryData        # Versioned object (if versioning enabled)
      <version-id>-objectMetadata.json
    multiparts/
      <upload-id>/
        multipartMetadata.json
        <part-number>.part

Note: The file system structure is an implementation detail and may change between releases. While files can be inspected during runtime, reusing persisted data across restarts is not officially supported.

Performance & Resources

S3Mock is designed for testing, not production workloads:

  • Disk: All objects are stored on the local filesystem — disk usage grows proportionally with stored data
  • Memory: Consumption scales with concurrent multipart uploads and in-flight requests
  • CI environments: Consider setting Docker resource limits (e.g., --memory=512m) to avoid contention with other services
  • Cleanup: By default, S3Mock deletes all stored data on shutdown. Set COM_ADOBE_TESTING_S3MOCK_STORE_RETAIN_FILES_ON_EXIT=true only when you need data to survive restarts

Architecture & Development

graph LR
    Client["AWS SDK / CLI / cURL"] -->|HTTP :9090 / HTTPS :9191| Controller
    subgraph S3Mock
        Controller["Controller<br/>(REST endpoints)"] -->|delegates| Service["Service<br/>(business logic)"]
        Service -->|coordinates| Store["Store<br/>(persistence)"]
        Store -->|read/write| FS["Filesystem"]
    end
Loading

Module Documentation:

Build & Run

Requirements: Java 25, Maven 3.9+, Docker (for Docker build and integration tests)

Build:

make install       # Full build with Docker
make skip-docker   # Skip Docker build

Run from source:

make run           # As Spring Boot application

# As Docker container
./mvnw clean package -pl server -am -DskipTests
docker run -p 9090:9090 -p 9191:9191 adobe/s3mock:latest

Run integration tests:

make integration-tests

Technology:

  • S3Mock is written in Kotlin 2.3+ (language/API compatibility: 2.2) with Spring Boot 4.0
  • All tests are written in Kotlin
  • JVM bytecode target: 17; building and running from source requires JDK 25 (per Spring Boot 4.x guidance), while the packaged artifacts run on Java 17+.

Contributing

Contributions are welcome! See Contributing Guide.

Governance: Project leads make final decisions — see developers in pom.xml.

Security: See Security Policy for reporting vulnerabilities. S3Mock uses GitHub Actions for SBOM generation and vulnerability scanning.

License

Licensed under the Apache License 2.0 - see LICENSE.

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About

A mock implementation of the AWS S3 API startable as Docker image, TestContainer, JUnit 4 rule, JUnit Jupiter extension or TestNG listener

Topics

kotlin java testing mock docker aws aws-s3 s3 junit amd64 arm64 testcontainers

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Apache-2.0 license

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5.0.0 Latest
Apr 8, 2026
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