Mobile-Web Data Sync

Shared Bucket Access

Shared Bucket Access enables document changes made through Couchbase SDKs and N1QL queries to be synchronized to Couchbase Lite clients, and vice versa. The following diagram shows different clients (mobile, web, desktop) writing data to the same bucket in Couchbase Server.

In previous releases, you either had to ensure all writes happened through Sync Gateway, or had to set up bucket shadowing to ensure that the security and replication metadata needed by mobile applications was preserved.

In this release, the metadata created by the Sync Gateway is abstracted from applications reading and writing data directly to Couchbase Server. Sync Gateway 1.5 utilizes a new feature of Couchbase Server 5.0 called XATTRs (eXtended ATTRibutes) to store that metadata into an external document fragment.

How to enable it

This new feature was made opt-in primarily out of consideration for existing customers upgrading from Sync Gateway 1.4. It ensures that their existing configs will continue to work as-is, and supports upgrade without bringing down the entire Sync Gateway cluster.

The getting started page includes step-by-step instructions to:

Install Couchbase Server 5.0 or above.
Configure Couchbase Server with RBAC.

Install Sync Gateway with a configuration file that enables Mobile-Web data synchronization. Another example is presented below.

{
    "databases": {
        "db": {
            "bucket": "my-bucket",
            "username": "my-user",
            "password": "my-password",
            "server": "http://localhost:8091",
            "enable_shared_bucket_access": true, (1)
            "import_docs": true (2)
        }
    }
}

1	The `enable_shared_bucket_access` property is used to enable Web-Mobile data sync.
2	The `import_docs` property is used to specify that this Sync Gateway node should perform import processing of incoming documents. `import_docs` can only be set to `true` on a single node.

enable_shared_bucket_access needs to be true on all nodes participating in such a configuration where as import_docs can only be set to true on a single node.

From then on, documents can be inserted on the Server directly (with N1QL or SDKs) or through the Sync Gateway REST API. The mobile metadata is no longer kept in the document, but in a system extended attribute in Couchbase Server.

When this feature is enabled, the REST API will include the following changes:

Purging — /{db}/_purge removes the document and its associated extended attributes
Updating — /{db}/{docid} will tombstone the active revision

Reference

The reference to the configuration properties can be found below.

$dbname.enable_shared_bucket_access to enable convergence for a given database.
$dbname.import_docs to give a particular Sync Gateway node the role of importing the documents.
$dbname.import_filter to select which document(s) to make aware to mobile clients.

Metadata Purge Interval

When this feature is enabled, mobile tombstones are not retained indefinitely. They will be purged based on the server’s metadata purge interval. To ensure tombstones are replicated to clients, you should set the server’s metadata purge interval based on your expected replication frequency (see the $dbname.enable_shared_bucket_access reference).

FAQ

How do I query the document’s sync metadata?

Starting in Couchbase Server 5.5, the N1QL query language supports the ability to select extended attributes (xattrs) where the document’s sync metadata is stored. The following query shows an example of that feature.

SELECT meta().xattrs._sync FROM `travel-sample` WHERE meta().id = "mydocId"

Prior to 5.5, there is no way to query the mobile metadata with shared_bucket_access_enabled: true.

The sync metadata is maintained internally by Sync Gateway and its structure can change at any time. It should not be used to drive business logic of applications. The direct use of the N1QL query is unsupported and must not be used in production environments.

How do I access a blob stored in Couchbase Lite?

How do I access an attachment from a WebApp?

Attachments can be accessed through Sync Gateway’s REST API using the /{db}/{doc}/{attachment} endpoint.

Migrating from Bucket Shadowing

As of Sync Gateway 1.5, the Bucket Shadowing feature is deprecated and no longer supported. The following steps outline a recommended method for migrating from Bucket Shadowing to the latest version with interoperability between Couchbase Server SDKs and Couchbase Mobile.

Follow the recommendations in the Couchbase Server documentation to upgrade all instances to 5.0.
Create a new bucket on Couchbase Server (bucket 2).
Install Sync Gateway 1.5 on a separate node with shared access enabled and connect it to the new bucket (bucket 2).
Setup a push replication from the Sync Gateway instance used for Bucket Shadowing to the Sync Gateway 1.5 instance.
Once the replication has completed, test your application is performing as expected.
Update the load balancer to direct incoming traffic to the Sync Gateway 1.5 instance when you are ready to upgrade.
Delete the first bucket (bucket 1).

bucket shadowing migration