docs/source/replication/bucket-replication-overview.rst

Bucket Replication

minio

Table of Contents

MinIO supports server-side and client-side replication of objects between source and destination buckets.

Server-Side Bucket Replication <minio-bucket-replication-serverside>

Configure per-bucket rules for automatically synchronizing objects between buckets within the same MinIO cluster or between two independent MinIO Clusters. MinIO applies rules as part of object write operations (e.g. PUT) and automatically synchronizes new objects and object mutations, such as new object versions or changes to object metadata.

MinIO server-side bucket replication only supports MinIO clusters for the remote replication target.

Client-side Bucket Replication <minio-bucket-replication-clientside>

Use The command process to synchronize objects between buckets within the same S3-compatible cluster or between two independent S3-compatible clusters. Client-side replication using mc mirror supports MinIO-to-S3 and similar replication configurations.

Server-Side Bucket Replication

MinIO server-side bucket replication is an automatic bucket-level configuration that synchronizes objects between a source and destination bucket. MinIO server-side replication requires the source and destination bucket be two separate MinIO clusters.

For each write operation to the bucket, MinIO checks all configured replication rules for the bucket and applies the matching rule with highest configured priority. MinIO synchronizes new objects and object mutations, such as new object versions or changes to object metadata. This includes metadata operations such as enabling or modifying object locking or retention settings.

MinIO server-side bucket replication is functionally similar to Amazon S3 replication while adding the following MinIO-only features:

• Source and destination bucket names can match, supporting site-to-site use cases such as Splunk or Veeam BC/DR.
• Simplified implementation than S3 bucket replication configuration, removing the need to configure settings like AccessControlTranslation, Metrics, and SourceSelectionCriteria.
• Active-Active (Two-Way) replication of objects between source and destination buckets.
• Multi-Site replication of objects between three or more MinIO deployments (New in RELEASE.2021-09-23T04-46-24Z).

Resynchronization (Disaster Recovery)

Resynchronization primarily supports recovery after partial or total loss of the data on a MinIO deployment using a healthy deployment in the replica configuration. Use the mc replicate resync command completely resynchronize the remote target (mc admin bucket remote) using the specified source bucket.

The resynchronization process checks all objects in the source bucket against all configured replication rules that include existing object replication <minio-replication-behavior-existing-objects>. For each object which matches a rule, the resynchronization process places the object into the replication queue <minio-replication-process> regardless of the object's current replication status <minio-replication-process>.

MinIO skips synchronizing those objects whose remote copy exactly match the source, including object metadata. MinIO otherwise does not prioritize or modify the queue with regards to the existing contents of the target.

mc replicate resync operates at the bucket level and does not support prefix-level granularity. Initiating resynchronization on a large bucket may result in a significant increase in replication-related load and traffic. Use this command with caution and only when necessary.

For buckets with object transition (Tiering) <minio-lifecycle-management-tiering> configured, replication resynchronization restores objects in a non-transitioned state with no associated transition metadata. Any data previously transitioned to the remote storage is therefore permanently disconnected from the remote MinIO deployment. For tiering configurations which specify an explicit human-readable prefix as part of the remote configuration, you can safely purge the transitioned data in that prefix to avoid costs associated to the "lost" data.

Replication of Delete Operations

MinIO supports replicating delete operations, where MinIO synchronizes deleting specific object versions and new delete markers <delete-marker-replication.html>. Delete operation replication uses the same replication process <minio-replication-process> as all other replication operations.

MinIO requires explicitly enabling versioned deletes and delete marker replication . Use the mc replicate add --replicate field to specify both or either delete and delete-marker to enable versioned deletes and delete marker replication respectively. To enable both, specify both strings using a comma separator delete,delete-marker.

For delete marker replication, MinIO begins the replication process after a delete operation creates the delete marker. MinIO uses the X-Minio-Replication-DeleteMarker-Status metadata field for tracking delete marker replication status. In active-active <minio-bucket-replication-serverside-twoway> replication configurations, MinIO may produce duplicate delete markers if both clusters concurrently create a delete marker for an object or if one or both clusters were down before the replication event synchronized.

For replicating the deletion of a specific object version, MinIO marks the object version as PENDING until replication completes. Once the remote target deletes that object version, MinIO deletes the object on the source. While this process ensures near-synchronized version deletion, it may result in listing operations returning the object version after the initial delete operation. MinIO uses the X-Minio-Replication-Delete-Status for tracking delete version replication status.

MinIO only replicates explicit client-driven delete operations. MinIO does not replicate objects deleted from the application of lifecycle management expiration rules <minio-lifecycle-management-expiration>. For active-active <minio-bucket-replication-serverside-twoway> configurations, set the same expiration rules on all of of the replication buckets to ensure consistent application of object expiration.

MinIO Trims Empty Object Prefixes on Source and Remote Bucket

If a delete operation removes the last object in a bucket prefix, MinIO recursively removes each empty part of the prefix up to the bucket root. MinIO only applies the recursive removal to prefixes created implicitly as part of object write operations - that is, the prefix was not created using an explicit directory creation command such as mc mb.

If a replication rule enables replication delete operations, the replication process also applies the implicit prefix trimming behavior on the destination MinIO cluster.

For example, consider a bucket photos with the following object prefixes:

• photos/2021/january/myphoto.jpg
• photos/2021/february/myotherphoto.jpg
• photos/NYE21/NewYears.jpg

photos/NYE21 is the only prefix explicitly created using mc mb. All other prefixes were implicitly created as part of writing the object located at that prefix.

• A command removes myphoto.jpg. MinIO automatically trims the empty /janaury prefix.
• A command then removes the myotherphoto.jpg. MinIO automatically trims the /february prefix and the now-empty /2021 prefix.
• A command removes the NewYears.jpg object. MinIO leaves the /NYE21 prefix remains in place since it was explicitly created.

Replication of Existing Objects

MinIO by default does not enable existing object replication. Objects created before replication was configured or while replication is disabled are not synchronized to the target deployment. Starting with mc RELEASE.2021-06-13T17-48-22Z <mc/releases/tag/RELEASE.2021-06-13T17-48-22Z> and minio RELEASE.2021-06-07T21-40-51Z <minio/releases/tag/RELEASE.2021-06-07T21-40-51Z>, MinIO supports enabling replication of existing objects in a bucket.

Enabling existing object replication marks all objects or object prefixes that satisfy the replication rules as eligible for synchronization to the source cluster, even if those objects were created prior to configuring or enabling replication. You can enable existing object replication while configuring or modifying a replication rule:

• For new replication rules, include "existing-objects" to the list of replication features specified to mc replicate add --replicate.
• For existing replication rules, add "existing-objects" to the list of existing replication features using mc replicate edit --replicate. You must specify all desired replication features when editing the replication rule.

Enabling existing object replication does not increase the priority of objects pending replication. MinIO uses the same core replication scanner and queue system <minio-replication-process> for detecting and synchronizing objects regardless of the enabled replication feature. The time required to fully synchronize a bucket depends on a number of factors, including but not limited to the current cluster replication load, overall cluster load, and the size of the namespace (all objects in the bucket).

If versioning was not previously enabled when configuring bucket replication, existing objects have a versionid = null. These objects do replicate.

MinIO existing object replication implements functionality similar to AWS: Replicating existing objects between S3 buckets without the overhead of contacting technical support.

Synchronous vs Asynchronous Replication

MinIO supports specifying either asynchronous (default) or synchronous replication for a given remote target.

With the default asynchronous replication, MinIO completes the originating PUT operation before placing the object into a replication queue <minio-replication-process>. The originating client may therefore see a successful PUT operation before the object is replicated. While this may result in stale or missing objects on the remote, it mitigates the risk of slow write operations due to replication load.

With synchronous replication, MinIO attempts to replicate the object prior to completing the originating PUT operation. MinIO returns a successful PUT operation whether or not the replication attempts succeeds. While this may result in more reliable synchronization between the source and remote target, it may also increase the time of each write operation due to replication load.

You must explicitly enable synchronous replication when configuring the remote target target using the mc admin bucket remote add command with the ~mc admin bucket remote add flag.

Replication Internals

This section documents internal replication behavior and is not critical to using or implementing replication. This documentation is provided strictly for learning and educational purposes.

Replication Process

MinIO uses a replication queuing system with multiple concurrent replication workers operating on that queue. MinIO continuously works to replicate and remove objects from the queue while scanning for new unreplicated objects to add to the queue.

MinIO sets the X-Amz-Replication-Status metadata field according to the replication state of the object:

Replication State	Description
PENDING	The object has not yet been replicated. MinIO applies this state if the object meets one of the configured replication rules on the bucket. MinIO continuously scans for PENDING objects not yet in the replication queue and adds them to the queue as space is available. For multi-site replication, objects remain in the PENDING state until replicated to all configured remotes for that bucket or bucket prefix.
COMPLETED	The object has successfully replicated to the remote cluster.
FAILED	The object failed to replicate to the remote cluster. MinIO continuously scans for FAILED objects not yet in the replication queue and adds them to the queue as space is available.
REPLICA	The object is itself a replica from a remote source.

The replication process generally has one of the following flows:

• PENDING -> COMPLETED
• PENDING -> FAILED -> COMPLETED

/replication/enable-server-side-one-way-bucket-replication /replication/enable-server-side-two-way-bucket-replication /replication/enable-server-side-multi-site-bucket-replication /replication/server-side-replication-resynchronize-remote

Client-Side Bucket Replication

The mc command mc mirror supports watching a source bucket and automatically replicating objects to a destination bucket.