Back to Source

Mirroring-based Back to Source

If a mirroring back-to-source rule is configured for an OBS bucket and the requested data is not found in the bucket, the system will retrieve the data, when the back-to-source rule applies to the data, from the origin server, upload it to the bucket, and then return it to the requesting client. This process does not interrupt services. Therefore, you can use this function to seamlessly migrate data from the origin server to OBS, or migrate services to OBS without being sensed by users, at low costs. Figure 1 illustrates the mirroring back-to-source process.

Figure 1 Process of mirroring-based back to source

Constraints

Bucket versions

• Only buckets of version 3.0 or later support mirroring-based back to source.

Time

• A mirroring back-to-source rule takes effect five minutes later after any change to the rule.

Regions

Back to source is only available in some regions. For details, see Function Overview.

Number of rules

• A maximum of 10 mirroring back-to-source rules can be configured for a bucket.

Functions

• Anonymous users cannot configure mirroring back-to-source rules for a bucket.

• Parallel file systems do not support mirroring back-to-source rules.
• A mirroring back-to-source rule is not compatible with the static website hosting function. Specifically, if a 404 error occurs when objects are downloaded from an OBS hosted static website domain, it does not trigger the mirroring back-to-source process.
• The bucket, to which a back-to-source rule is configured, cannot be specified as the source site.
• Currently, mirroring-based back to source from private buckets is only supported for some cloud vendors.
• The origin server cannot transfer data in Transfer-Encoding: chunked mode. That is, the response to the request for downloading an object from the origin server must contain the Content-Length header to specify the size of the source object.

  Specifically, in the Create/Edit Back-to-Source Rule window, you cannot specify Accept-Encoding for Do not pass specified parameters under the Pass all parameters option of HTTP Header Pass Rule.

  Figure 2 Configuration method
  

Permissions

• To configure, obtain, or delete mirroring back-to-source rules, you must have the Tenant Administrator permission assigned by using IAM.
• Mirroring-based back to source requires that you create an IAM agency to delegate OBS to pull data from its origin server. The permissions the agency should assign to OBS include obs:object:PutObject, obs:object:GetObject, obs:bucket:ListBucket, and obs:object:AbortMultipartUpload.
• If SSE-KMS is enabled for a bucket, the kms:cmk:get, kms:cmk:list, kms:cmk:create, kms:dek:create, kms:dek:crypto, and kms:dek:crypto permissions must be configured for the IAM agency for OBS.

Creating a Mirroring Back-to-Source Rule

You can create mirroring back-to-source rules on OBS Console or by calling APIs.