• S3Mock
• Changelog
• Supported S3 operations
• Usage
  • Usage of AWS S3 SDKs
    • Path-style vs Domain-style access
    • Presigned URLs
  • Usage of AWS CLI
  • Usage of plain HTTP
  • S3Mock configuration options
  • S3Mock Docker
    • Start using the command-line
    • Start using the Fabric8 Docker-Maven-Plugin
    • Start using Testcontainers
    • Start using Docker compose
      • Simple example
      • Expanded example
  • S3Mock Java
    • Start using the JUnit4 Rule
    • Start using the JUnit5 Extension
    • Start using the TestNG Listener
    • Start programmatically
• File System Structure
  • Root-Folder
  • Buckets
  • Objects
  • Multipart Uploads
• Build & Run
  • Java
  • Kotlin
• Contributing
• Licensing

S3Mock is a lightweight server that implements parts of the Amazon S3 API.
It has been created to support local integration testing by reducing infrastructure dependencies.

The S3Mock server can be started as a standalone Docker container, using Testcontainers, JUnit4, JUnit5 and TestNG support, or programmatically.

See GitHub releases.
See also the changelog for detailed information about changes in releases and changes planned for future releases.

Of these operations of the Amazon S3 API, all marked ✅ are supported by S3Mock:

S3Mock can be used with any of the available AWS S3 SDKs.

The Integration Tests contain various examples of how to use the S3Mock with the AWS SDK for Java v1 and v2 in Kotlin. The modules below testsupport contain examples in Java.

S3Client or S3Presigner instances are created here:

• Kotlin: Integration Test base class
• Java: S3Mock unit test starter base class

AWS S3 SDKs usually use domain-style access by default. Configuration is needed for path-style access.

S3Mock currently only supports path-style access (e.g., https://localhost:9090/bucket/someKey).

Domain-style access to buckets (e.g., https://bucket.localhost:9090/someKey) does not work. This is due to the fact that the domain localhost is special and does not allow for subdomain access without modifications to the operating system.

S3 SDKs can be used to create presigned URLs, the S3 API supports access through those URLs.

S3Mock will accept presigned URLs, but it ignores all parameters.
For instance, S3Mock does not verify the HTTP verb that the presigned uri was created with, and it does not validate whether the link is expired or not.

S3 SDKs can be used to create presigned URLs pointing to S3Mock if they're configured for path-style access. See the "Usage of..." section above for links to examples on how to use the SDK with presigned URLs.

S3Mock can be used with the AWS CLI. Setting the --endpoint-url enables path-style access.

Examples:

Create bucket

aws s3api create-bucket --bucket my-bucket --endpoint-url=https://localhost:9090

Put object

aws s3api put-object --bucket my-bucket --key my-file --body ./my-file --endpoint-url=https://localhost:9090

Get object

aws s3api get-object --bucket my-bucket --key my-file --endpoint-url=https://localhost:9090 my-file-output

As long as the requests work with the S3 API, they will work with S3Mock as well.

Examples:

Create bucket

curl --request PUT "https://localhost:9090/my-test-bucket/"

Put object

curl --request PUT --upload-file ./my-file https://localhost:9090/my-test-bucket/my-file

Get object

curl --request GET https://localhost:9090/my-test-bucket/my-file

The mock can be configured with the following environment variables:

• validKmsKeys: list of KMS Key-Refs that are to be treated as valid.
  • KMS keys must be configured as valid ARNs in the format of "arn:aws:kms:region:acct-id:key/key-id", for example "arn:aws:kms:us-east-1:1234567890:key/valid-test-key-id"
  • The list must be comma separated keys like arn-1, arn-2
  • When requesting with KMS encryption, the key ID is passed to the SDK / CLI, in the example above this would be "valid-test-key-id".
  • S3Mock does not implement KMS encryption, if a key ID is passed in a request, S3Mock will just validate if a given Key was configured during startup and reject the request if the given Key was not configured.
• initialBuckets: list of names for buckets that will be available initially.
  • The list must be comma separated names like bucketa, bucketb
• root: the base directory to place the temporary files exposed by the mock. If S3Mock is started in Docker, a volume must be mounted as the root directory, see examples below.
• debug: set to true to enable Spring Boot's debug output.
• trace: set to true to enable Spring Boot's trace output.
• retainFilesOnExit: set to true to let S3Mock keep all files that were created during its lifetime. Default is false, all files are removed if S3Mock shuts down.

The S3Mock Docker container is the recommended way to use S3Mock.
It is released to Docker Hub.
The container is lightweight, built on top of the official Linux Alpine image.

If needed, configure memory and cpu limits for the S3Mock docker container.

The JVM will automatically use half the available memory.

Starting on the command-line:

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

The port 9090 is for HTTP, port 9191 is for HTTPS.

Example with configuration via environment variables:

docker run -p 9090:9090 -p 9191:9191 -e initialBuckets=test -e debug=true -t adobe/s3mock

Our integration tests are using the Amazon S3 Client to verify the server functionality against the S3Mock. During the Maven build, the Docker image is started using the docker-maven-plugin and the corresponding ports are passed to the JUnit test through the maven-failsafe-plugin. See BucketV2IT as an example on how it's used in the code.

This way, one can easily switch between calling the S3Mock or the real S3 endpoint and this doesn't add any additional Java dependencies to the project.

The S3MockContainer is a Testcontainer implementation that comes pre-configured exposing HTTP and HTTPS ports. Environment variables can be set on startup.

The example S3MockContainerJupiterTest demonstrates the usage with JUnit 5. The example S3MockContainerManualTest demonstrates the usage with plain Java.

Testcontainers provides integrations for JUnit 4, JUnit 5 and Spock.
For more information, visit the Testcontainers website.

To use the S3MockContainer, use the following Maven artifact in test scope:

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

Create a file docker-compose.yml

services:
  s3mock:
    image: adobe/s3mock:latest
    environment:
      - initialBuckets=bucket1
    ports:
      - 9090:9090

Start with docker compose up -d

Stop with docker compose down

Suppose we want to see what S3Mock is persisting, and look at the logs it generates in detail.

A local directory is needed, let's call it locals3root. This directory must be mounted as a volume into the Docker container when it's started, and that mounted volume must then be configured as the root for S3Mock. Let's call the mounted volume inside the container containers3root. S3Mock will delete all files when it shuts down, retainFilesOnExit=true tells it to leave all files instead.

Also, to see debug logs, debug=true must be configured for S3Mock.

Create a file docker-compose.yml

services:
  s3mock:
    image: adobe/s3mock:latest
    environment:
      - debug=true
      - retainFilesOnExit=true
      - root=containers3root
    ports:
      - 9090:9090
      - 9191:9191
    volumes:
      - ./locals3root:/containers3root

Create a directory locals3root.

Start with docker compose up -d

Create a bucket "my-test-bucket" with curl --request PUT "https://localhost:9090/my-test-bucket/"

Stop with docker compose down

Look into the directory locals3root where metadata and contents of the bucket are stored.

$ mkdir s3mock-mounttest
$ cd s3mock-mounttest
$ mkdir locals3root
$ cat docker-compose.yml
services:
  s3mock:
    image: adobe/s3mock:latest
    environment:
      - debug=true
      - retainFilesOnExit=true
      - root=containers3root
    ports:
      - 9090:9090
      - 9191:9191
    volumes:
      - ./locals3root:/containers3root

$ docker compose up -d
[+] Running 2/2
 ✔ Network s3mock-mounttest_default     Created
 ✔ Container s3mock-mounttest-s3mock-1  Started
$ curl --request PUT "https://localhost:9090/my-test-bucket/"
$ docker compose down
[+] Running 2/0
 ✔ Container s3mock-mounttest-s3mock-1  Removed
 ✔ Network s3mock-mounttest_default     Removed
 
$ ls locals3root
my-test-bucket
$ ls locals3root/my-test-bucket
bucketMetadata.json

S3Mock Java libraries are released and published to the Sonatype Maven Repository and subsequently published to the official Maven mirrors.

S3Mock is built using Spring Boot, if projects use S3Mock by adding the dependency to their project and starting the S3Mock during a JUnit test, classpaths of the tested application and of the S3Mock are merged, leading to unpredictable and undesired effects such as class conflicts or dependency version conflicts.
This is especially problematic if the tested application itself is a Spring (Boot) application, as both applications will load configurations based on availability of certain classes in the classpath, leading to unpredictable runtime behaviour.

This is the opposite of what software engineers are trying to achieve when thoroughly testing code in continuous integration...

S3Mock dependencies are updated regularly, any update could break any number of projects.
See also issues labelled "dependency-problem".

See also the Java section below

The example S3MockRuleTest demonstrates the usage of the S3MockRule, which can be configured through a builder.

To use the JUnit4 Rule, use the following Maven artifact in test scope:

<dependency>
 <groupId>com.adobe.testing</groupId>
 <artifactId>s3mock-junit4</artifactId>
 <version>...</version>
 <scope>test</scope>
</dependency>

The S3MockExtension can currently be used in two ways:

1. Declaratively using @ExtendWith(S3MockExtension.class) and by injecting a properly configured instance of AmazonS3 client and/or the started S3MockApplication to the tests. See examples: S3MockExtensionDeclarativeTest (for SDKv1) or S3MockExtensionDeclarativeTest (for SDKv2)

2. Programmatically using @RegisterExtension and by creating and configuring the S3MockExtension using a builder. See examples: S3MockExtensionProgrammaticTest (for SDKv1) or S3MockExtensionProgrammaticTest (for SDKv2)

To use the JUnit5 Extension, use the following Maven artifact in test scope:

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

The example S3MockListenerXMLConfigurationTest demonstrates the usage of the S3MockListener, which can be configured as shown in testng.xml. The listener bootstraps the S3Mock application before TestNG execution starts and shuts down the application just before the execution terminates. Please refer to IExecutionListener from the TestNG API.

To use the TestNG Listener, use the following Maven artifact in test scope:

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

Include the following dependency and use one of the start methods in com.adobe.testing.s3mock.S3MockApplication:

<dependency>
  <groupId>com.adobe.testing</groupId>
  <artifactId>s3mock</artifactId>
  <version>...</version>
</dependency>

S3Mock stores Buckets, Objects, Parts and other data on disk.
This lets users inspect the stored data while the S3Mock is running.
If the config property retainFilesOnExit is set to true, this data will not be deleted when S3Mock is shut down.

S3Mock stores buckets and objects a root-folder.

This folder is expected to be empty when S3Mock starts. See also FYI above.

/<root-folder>/

Buckets are stored as a folder with their name as created through the S3 API directly below the root:

/<root-folder>/<bucket-name>/

BucketMetadata is stored in a file in the bucket directory, serialized as JSON.
BucketMetadata contains the "key" -> "uuid" dictionary for all objects uploaded to this bucket among other data.

/<root-folder>/<bucket-name>/bucketMetadata.json

Objects are stored in folders below the bucket they were created in. A folder is created that uses the Object's UUID assigned in the BucketMetadata as a name.

/<root-folder>/<bucket-name>/<uuid>/

Object data is stored below that UUID folder.

Binary data is always stored in a file binaryData

/<root-folder>/<bucket-name>/<uuid>/binaryData

Object metadata is serialized as JSON and stored as objectMetadata.json

/<root-folder>/<bucket-name>/<uuid>/objectMetadata.json

Object ACL is serialized as JSON and stored as objectAcl.xml

/<root-folder>/<bucket-name>/<uuid>/objectAcl.json

Multipart Uploads are created in a bucket using object keys and an uploadId.
The object is assigned a UUID within the bucket (stored in BucketMetadata).
The Multipart upload metadata is currently not stored on disk.

The multiparts folder is created below the bucket folder and named with the uploadId:

/<root-folder>/<bucket-name>/multiparts/<uploadId>/

The multiparts metadata file is created below the folder named with the uploadId:

/<root-folder>/<bucket-name>/multiparts/<uploadId>/multipartMetadata.json

Each part is stored in the parts folder with the partNo as name and .part as a suffix.

/<root-folder>/<bucket-name>/multiparts/<uploadId>/<partNo>.part

Once the MultipartUpload is completed, the uploadId folder is deleted.

To build this project, you need Docker, JDK 17 or higher, and Maven:

./mvnw clean install

If you want to skip the Docker build, pass the optional parameter "skipDocker":

./mvnw clean install -DskipDocker

You can run the S3Mock from the sources by either of the following methods:

• Run or Debug the class com.adobe.testing.s3mock.S3MockApplication in the IDE.
• using Docker:
  • ./mvnw clean package -pl server -am -DskipTests
  • docker run -p 9090:9090 -p 9191:9191 -t adobe/s3mock:latest
• using the Docker Maven plugin:
  • ./mvnw clean package docker:start -pl server -am -DskipTests -Ddocker.follow -Dit.s3mock.port_http=9090 -Dit.s3mock.port_https=9191 (stop with ctrl-c)

Once the application is started, you can execute the *IT tests from your IDE.

This repo is built with Java 17, output is currently bytecode compatible with Java 17.

The Integration Tests are built in Kotlin.

Contributions are welcomed! Read the Contributing Guide for more information.

This project is licensed under the Apache V2 License. See LICENSE for more information.