Object Replication (Azure Blob Storage)
What it is
Object replication asynchronously copies block blobs from a source container in one storage account to a destination container in another account. The accounts can be in the same or different regions. It is useful when you want selected blob data near readers or in a separate location.
Why it exists
It performs a one-way, rule-based copy without requiring an application copy job. It is not synchronous geo-replication and does not mean the destination is immediately ready for a failover; replication can lag and the application needs a plan to use the destination.
Key ideas
- Block blobs only — append blobs and page blobs are not supported.
- Prerequisites matter — enable blob versioning on both accounts and change feed on the source account. These features can add cost.
- A replication policy (defined on the source account) contains one or more rules: each rule maps a source container to a destination container, with an optional prefix filter (only blobs matching the prefix are copied).
- Copies are asynchronous: source and destination are not immediately in sync. Check replication status rather than assuming a particular object has arrived.
- The service copies blob contents, metadata, properties, and versions. It does not replicate snapshots, and destination versions receive new version IDs.
- It has important limits: hierarchical namespace accounts and blobs uploaded through Data Lake Storage APIs are not supported; archive-tier blobs cause replication to fail.
Northwind example
Northwind publishes completed product photos from a UK source account to a European destination account for lower-latency reads. A rule sends only blobs under published/, not drafts. Before the storefront reads a newly published photo from the destination, the release process checks that object replication has completed; otherwise it reads from the source. This is a distribution pattern, not an instant backup or automatic failover.
How it fits (diagram)
Exam notes
- Prerequisites: source change feed and versioning on both accounts.
- It replicates block blobs one way and asynchronously; it is not whole-account, synchronous replication.
- Use rules and status checks for controlled data distribution or recovery design.
Related
blob-storage · blob-versioning · storage-account · storage-performance
📘 Source: Microsoft Learn — Object Replication