S3 API

Slack Docker Pulls GitHub edit source

Alluxio supports a RESTful API that is compatible with the basic operations of the Amazon S3 API.

The Alluxio S3 API should be used by applications designed to communicate with an S3-like storage and would benefit from the other features provided by Alluxio, such as data caching, data sharing with file system based applications, and storage system abstraction (e.g., using Ceph instead of S3 as the backing store). For example, a simple application that downloads reports generated by analytic tasks can use the S3 API instead of the more complex file system API.

Limitations and Disclaimers

Alluxio Filesystem Limitations

Only top-level Alluxio directories are treated as buckets by the S3 API.

  • Hence the root directory of the Alluxio filesystem is not treated as an S3 bucket. Any root-level objects (eg: alluxio://file) will be inaccessible through the Alluxio S3 API.
  • To treat sub-directories as a bucket, the separator : must be used in the bucket name (eg: s3://sub:directory:bucket/file).
    • Note that this is purely a convenience feature and hence is not returned by API Actions such as ListBuckets.

Alluxio uses / as a reserved separator. Therefore, any S3 paths with objects or folders named / (eg: s3://example-bucket//) will cause undefined behavior.

No Bucket Virtual Hosting

Virtual hosting of buckets is not supported in the Alluxio S3 API. Therefore, S3 clients must utilize path-style requests (i.e: http://s3.amazonaws.com/{bucket}/{object} and NOT http://{bucket}.s3.amazonaws.com/{object}).

S3 Writes Implicitly Overwrite

As described in the AWS S3 docs for PutObject:

Amazon S3 is a distributed system. If it receives multiple write requests for the same object simultaneously, it overwrites all but the last object written. Amazon S3 does not provide object locking; if you need this, make sure to build it into your application layer or use versioning instead.

  • Note that at the moment the Alluxio S3 API does not support object versioning

Alluxio S3 will overwrite the existing key and the temporary directory for multipart upload.

Folders in ListObjects(V2)

All sub-directories in Alluxio will be returned in ListObjects(V2) as 0-byte folders. This behavior is in accordance with if you used the AWS S3 console to create all parent folders for each object.

Tagging & Metadata Limits

User-defined tags on buckets & objects are limited to 10 and obey the S3 tag restrictions.

The maximum size for user-defined metadata in PUT-requests is 2KB by default in accordance with S3 object metadata restrictions. Set the property key alluxio.proxy.s3.header.metadata.max.size to change this behavior.

Performance Implications

The S3 API leverages the Alluxio REST proxy , introducing an additional network hop for Alluxio clients. For optimal performance, it is recommended to run the proxy server and an Alluxio worker on each compute node. It is also recommended to put all the proxy servers behind a load balancer.

Global request headers

Header Content Description
Authorization AWS4-HMAC-SHA256 Credential={user}/..., SignedHeaders=..., Signature=... There is currently no support for access & secret keys in the Alluxio S3 API. The only supported authentication scheme is the SIMPLE authentication type. By default, the user that is used to perform any operations is the user that was used to launch the Alluxio proxy process.

Therefore this header is used exclusively to specify an Alluxio ACL username to perform an operation with. In order to remain compatible with other S3 clients, the header is still expected to follow the AWS Signature Version 4 format.

When supplying an access key to an S3 client, put the intended Alluxio ACL username. The secret key is unused so you may use any dummy value.

Supported S3 API Actions

The following table describes the support status for current S3 API Actions:

S3 API Action Supported Headers Supported Query Parameters
AbortMultipartUpload
  • None
N/A
CompleteMultipartUpload
  • None
N/A
CopyObject
  • Content-Type,
  • x-amz-copy-source,
  • x-amz-metadata-directive,
  • x-amz-tagging-directive,
  • x-amz-tagging
N/A
CreateBucket
  • None
N/A
CreateMultipartUpload
  • None
N/A
DeleteBucket
  • None
N/A
DeleteBucketTagging
  • None
N/A
DeleteObject
  • None
N/A
DeleteObjects
  • None
N/A
DeleteObjectTagging
  • None
  • None
GetBucketTagging
  • None
N/A
GetObject
  • Range
  • None
GetObjectTagging
  • None
  • None
HeadObject
  • None
  • None
ListBuckets N/A N/A
ListObjects
  • None
  • delimiter,
  • encoding-type,
  • marker,
  • max-keys,
  • prefix
ListObjectsV2
  • None
  • continuation-token,
  • delimiter,
  • encoding-type,
  • max-keys,
  • prefix,
  • start-after
ListParts
  • None
  • None
PutBucketTagging
  • None
N/A
PutObject
  • Content-Length,
  • Content-MD5,
  • Content-Type,
  • x-amz-tagging
N/A
PutObjectTagging
  • None
  • None
UploadPart
  • Content-Length,
  • Content-MD5
N/A

Property Keys

The following table contains the configurable Alluxio property keys which pertain to the Alluxio S3 API.

Property NameDefaultDescription
alluxio.proxy.s3.complete.multipart.upload.keepalive.time.interval 30sec The complete multipart upload keepalive time.
alluxio.proxy.s3.complete.multipart.upload.pool.size 20 The complete multipart upload thread pool size.
alluxio.proxy.s3.deletetype ALLUXIO_AND_UFS Delete type when deleting buckets and objects through S3 API. Valid options are `ALLUXIO_AND_UFS` (delete both in Alluxio and UFS), `ALLUXIO_ONLY` (delete only the buckets or objects in Alluxio namespace).
alluxio.proxy.s3.header.metadata.max.size 2KB The maximum size to allow for user-defined metadata in S3 PUTrequest headers. Set to 0 to disable size limits.
alluxio.proxy.s3.multipart.temporary.dir.suffix _s3_multipart_tmp Suffix for the directory which holds parts during a multipart upload.
alluxio.proxy.s3.multipart.upload.cleaner.pool.size 1 The abort multipart upload cleaner pool size.
alluxio.proxy.s3.multipart.upload.cleaner.retry.count 3 The retry count when aborting a multipart upload fails.
alluxio.proxy.s3.multipart.upload.cleaner.retry.delay 10sec The retry delay time when aborting a multipart upload fails.
alluxio.proxy.s3.multipart.upload.timeout 10min The timeout for aborting proxy s3 multipart upload automatically.
alluxio.proxy.s3.writetype CACHE_THROUGH Write type when creating buckets and objects through S3 API. Valid options are `MUST_CACHE` (write will only go to Alluxio and must be stored in Alluxio), `CACHE_THROUGH` (try to cache, write to UnderFS synchronously), `ASYNC_THROUGH` (try to cache, write to UnderFS asynchronously), `THROUGH` (no cache, write to UnderFS synchronously).

Example Usage

S3 API Actions


AbortMultipartUpload


CompleteMultipartUpload


CopyObject


CreateBucket


CreateMultipartUpload


DeleteBucket


DeleteBucketTagging


DeleteObject


DeleteObjects


DeleteObjectTagging


GetBucketTagging


GetObject


GetObjectTagging


HeadObject


ListBuckets


ListObjects


ListObjectsV2


ListParts


PutBucketTagging


PutObject


PutObjectTagging


UploadPart


Python S3 Client

Tested for Python 2.7.

Create a connection:

Please note you have to install boto package first.

$ pip install boto
import boto
import boto.s3.connection

conn = boto.connect_s3(
    aws_access_key_id = '',
    aws_secret_access_key = '',
    host = 'localhost',
    port = 39999,
    path = '/api/v1/s3',
    is_secure=False,
    calling_format = boto.s3.connection.OrdinaryCallingFormat(),
)

Authenticating as a user:

By default, authenticating with no access_key_id uses the user that was used to launch the proxy as the user performing the file system actions.

Set the aws_access_key_id to a different username to perform the actions under a different user.

Create a bucket

bucketName = 'bucket-for-testing'
bucket = conn.create_bucket(bucketName)

List all buckets owned by the user

Authenticating as a user is necessary to have buckets returned by this operation.

conn = boto.connect_s3(
    aws_access_key_id = 'testuser',
    aws_secret_access_key = '',
    host = 'localhost',
    port = 39999,
    path = '/api/v1/s3',
    is_secure=False,
    calling_format = boto.s3.connection.OrdinaryCallingFormat(),
)

conn.get_all_buckets()

PUT a small object

smallObjectKey = 'small.txt'
smallObjectContent = 'Hello World!'

key = bucket.new_key(smallObjectKey)
key.set_contents_from_string(smallObjectContent)

Get the small object

assert smallObjectContent == key.get_contents_as_string()

Upload a large object

Create a 8MB file on local file system.

$ dd if=/dev/zero of=8mb.data bs=1048576 count=8

Then use python S3 client to upload this as an object

largeObjectKey = 'large.txt'
largeObjectFile = '8mb.data'

key = bucket.new_key(largeObjectKey)
with open(largeObjectFile, 'rb') as f:
    key.set_contents_from_file(f)
with open(largeObjectFile, 'rb') as f:
    largeObject = f.read()

Get the large object

assert largeObject == key.get_contents_as_string()

Delete the objects

bucket.delete_key(smallObjectKey)
bucket.delete_key(largeObjectKey)

Initiate a multipart upload

mp = bucket.initiate_multipart_upload(largeObjectKey)

Upload parts

import math, os

from filechunkio import FileChunkIO

# Use a chunk size of 1MB (feel free to change this)
sourceSize = os.stat(largeObjectFile).st_size
chunkSize = 1048576
chunkCount = int(math.ceil(sourceSize / float(chunkSize)))

for i in range(chunkCount):
    offset = chunkSize * i
    bytes = min(chunkSize, sourceSize - offset)
    with FileChunkIO(largeObjectFile, 'r', offset=offset, bytes=bytes) as fp:
        mp.upload_part_from_file(fp, part_num=i + 1)

Complete the multipart upload

mp.complete_upload()

Abort the multipart upload

Non-completed uploads can be aborted.

mp.cancel_upload()

Delete the bucket

bucket.delete_key(largeObjectKey)
conn.delete_bucket(bucketName)