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When using the s3proxy as a proxy for S3 -> Azure Blob Storage, one needs to set the authentication parameters. When running in a container, these can be exposed via environment variables, but are currently not passed through to the jclouds config.

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S3Proxy implements the S3 API and proxies requests, enabling several use cases:

  • translation from S3 to Backblaze B2, EMC Atmos, Google Cloud, Microsoft Azure, and OpenStack Swift
  • testing without Amazon by using the local filesystem
  • extension via middlewares
  • embedding into Java applications

Usage with Docker

Docker Hub hosts a Docker image and has instructions on how to run it.

Usage without Docker

Users can download releases from GitHub. Developers can build the project by running mvn package which produces a binary at target/s3proxy. S3Proxy requires Java 8 or newer to run.

Configure S3Proxy via a properties file. An example using the local file system as the storage backend with anonymous access:


First create the filesystem basedir:

mkdir /tmp/s3proxy

Next run S3Proxy. Linux and Mac OS X users can run the executable jar:

chmod +x s3proxy
s3proxy --properties s3proxy.conf

Windows users must explicitly invoke java:

java -jar s3proxy --properties s3proxy.conf

Finally test by creating a bucket then listing all the buckets:

$ curl --request PUT http://localhost:8080/testbucket

$ curl http://localhost:8080/
<?xml version="1.0" ?><ListAllMyBucketsResult xmlns=""><Owner><ID>75aa57f09aa0c8caeab4f8c24e99d10f8e7faeebf76c078efc7c6caea54ba06a</ID><DisplayName></DisplayName></Owner><Buckets><Bucket><Name>testbucket</Name><CreationDate>2015-08-05T22:16:24.000Z</CreationDate></Bucket></Buckets></ListAllMyBucketsResult>

Usage with Java

Maven Central hosts S3Proxy artifacts and the wiki has instructions on Java use.

Supported storage backends

  • atmos
  • aws-s3 (Amazon-only)
  • azureblob
  • b2
  • filesystem (on-disk storage)
  • google-cloud-storage
  • openstack-swift
  • rackspace-cloudfiles-uk and rackspace-cloudfiles-us
  • s3 (all implementations)
  • transient (in-memory storage)

See the wiki for examples of configurations.

Assigning buckets to backends

S3Proxy can be configured to assign buckets to different backends with the same credentials. The configuration in the properties file is as follows:


In addition to the explicit names, glob syntax can be used to configure many buckets for a given backend.

A bucket (or a glob) cannot be assigned cannot be assigned to multiple backends.


S3Proxy can modify its behavior based on middlewares:


S3Proxy has broad compatibility with the S3 API, however, it does not support:

  • ACLs other than private and public-read
  • BitTorrent hosting
  • bucket logging
  • bucket policies
  • CORS bucket operations like getting or setting the CORS configuration for a bucket. S3Proxy only supports a static configuration (see below).
  • hosting static websites
  • object server-side encryption
  • object tagging
  • object versioning, see #74
  • POST upload policies, see #73
  • requester pays buckets
  • select object content

S3Proxy emulates the following operations:

  • copy multi-part objects, see #76

S3Proxy has basic CORS preflight and actual request/response handling. It can be configured within the properties file (and corresponding ENV variables for Docker):

s3proxy.cors-allow-origins=https://example\.com https://.+\.example\.com https://example\.cloud
s3proxy.cors-allow-methods=GET PUT
s3proxy.cors-allow-headers=Accept Content-Type

CORS cannot be configured per bucket. s3proxy.cors-allow-all=true will accept any origin and header. Actual CORS requests are supported for GET, PUT and POST methods.

The wiki collects compatibility notes for specific storage backends.



  • Apache jclouds provides storage backend support for S3Proxy
  • Ceph s3-tests help maintain and improve compatibility with the S3 API
  • fake-s3, gofakes3, minio, S3 ninja, and s3rver provide functionality similar to S3Proxy when using the filesystem backend
  • GlacierProxy and SwiftProxy provide similar functionality for the Amazon Glacier and OpenStack Swift APIs
  • s3mock mocks the S3 API for Java/Scala projects
  • sbt-s3 runs S3Proxy via the Scala Build Tool
  • swift3 provides an S3 middleware for OpenStack Swift
  • Zenko provide similar multi-cloud functionality


Copyright (C) 2014-2021 Andrew Gaul

Licensed under the Apache License, Version 2.0