S3 API

The Simple Storage Service (S3) API is a de-facto standard for object storage originally developed by Amazon Web Services. Arvados supports accessing files in Keep using the S3 API.

S3 is supported by many “cloud native” applications, and client libraries exist in many languages for programmatic access.

Endpoints and Buckets

To access Arvados S3 using an S3 client library, you must tell it to use the URL of the keep-web server (this is Services.WebDAVDownload.ExternalURL in the public configuration) as the custom endpoint. The keep-web server will decide to treat it as an S3 API request based on the presence of an AWS-format Authorization header. Requests without an Authorization header, or differently formatted Authorization, will be treated as WebDAV .

The “bucket name” is an Arvados collection uuid, portable data hash, or project uuid.

Path-style and virtual host-style requests are supported.

A path-style request uses the hostname indicated by Services.WebDAVDownload.ExternalURL, with the bucket name in the first path segment: https://download.example.com/zzzzz-4zz18-asdfgasdfgasdfg/.
A virtual host-style request uses the hostname pattern indicated by Services.WebDAV.ExternalURL, with a bucket name in place of the leading *: https://zzzzz-4zz18-asdfgasdfgasdfg.collections.example.com/.

If you have wildcard DNS, TLS, and routing set up, an S3 client configured with endpoint collections.example.com should work regardless of which request style it uses.

Supported Operations

ListObjects

Supports the following request query parameters:

delimiter
marker
max-keys
prefix

GetObject

Supports the Range header.

PutObject

Can be used to create or replace a file in a collection.

An empty PUT with a trailing slash and Content-Type: application/x-directory will create a directory within a collection if Arvados configuration option Collections.S3FolderObjects is true.

Missing parent/intermediate directories within a collection are created automatically.

Cannot be used to create a collection or project.

DeleteObject

Can be used to remove files from a collection.

If used on a directory marker, it will delete the directory only if the directory is empty.

HeadBucket

Can be used to determine if a bucket exists and if client has read access to it.

HeadObject

Can be used to determine if an object exists and if client has read access to it.

GetBucketVersioning

Bucket versioning is presently not supported, so this will always respond that bucket versioning is not enabled.

Authorization mechanisms

Keep-web accepts AWS Signature Version 4 (AWS4-HMAC-SHA256) as well as the older V2 AWS signature.

If your client uses V4 signatures exclusively: use the Arvados token’s UUID part as AccessKey, and its secret part as SecretKey. This is preferred.
If your client uses V2 signatures, or a combination of V2 and V4, or the Arvados token UUID is unknown: use the secret part of the Arvados token for both AccessKey and SecretKey.

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