S3 Cross-Region Replication: Complete Guide for AWS SysOps Administrator Associate Exam
What is S3 Cross-Region Replication (CRR)?
S3 Cross-Region Replication is an Amazon S3 feature that automatically and asynchronously copies objects from a source bucket in one AWS Region to a destination bucket in a different AWS Region. This replication happens in the background and ensures your data is available across multiple geographic locations.
Why is S3 Cross-Region Replication Important?
• Disaster Recovery: Protects your data against regional outages by maintaining copies in separate geographic locations
• Compliance Requirements: Helps meet regulatory requirements that mandate data storage in specific geographic regions
• Latency Reduction: Allows users in different regions to access data from a closer location, improving performance
• Data Sovereignty: Enables keeping copies of data in regions that align with local data residency laws
• Business Continuity: Ensures operations can continue even if one region becomes unavailable
How S3 Cross-Region Replication Works
Prerequisites:
• Versioning must be enabled on both source and destination buckets
• Source and destination buckets must be in different AWS Regions
• S3 must have permissions to replicate objects on your behalf (IAM role)
• If the buckets are owned by different accounts, the destination bucket owner must grant permissions
Replication Process:
1. When a new object is uploaded to the source bucket, S3 detects the change
2. S3 reads the replication configuration
3. The object is copied asynchronously to the destination bucket
4. Metadata, ACLs, and tags are preserved during replication
5. Storage class can be changed during replication if configured
Key Configuration Options:
• Replication Rules: Define which objects to replicate using prefixes or tags
• Storage Class: Specify a different storage class for replicated objects
• Replication Time Control (RTC): Provides SLA-backed replication within 15 minutes
• Delete Marker Replication: Optional setting to replicate delete markers
• Replica Modification Sync: Syncs metadata changes between replicas
What Gets Replicated:
• New objects created after replication is enabled
• Object metadata and tags
• Object ACL updates
• Objects encrypted with SSE-S3, SSE-KMS (with additional configuration), or unencrypted objects
What Does NOT Get Replicated:
• Objects that existed before replication was enabled (use S3 Batch Replication for these)
• Objects in the source bucket that are replicas from another replication rule
• Objects encrypted with SSE-C (customer-provided keys)
• Delete operations (by default, unless delete marker replication is enabled)
• Objects in Glacier or Glacier Deep Archive storage classes
Exam Tips: Answering Questions on S3 Cross-Region Replication
Key Points to Remember:
1. Versioning is Mandatory: When you see a question about CRR, remember that versioning must be enabled on BOTH buckets. If versioning is not mentioned as enabled, CRR will not work.
2. Existing Objects: CRR only replicates objects uploaded AFTER the rule is created. For existing objects, S3 Batch Replication is required.
3. Delete Behavior: By default, delete markers are NOT replicated. This is a common exam topic. If the question asks about maintaining delete synchronization, delete marker replication must be explicitly enabled.
4. Replication Time Control: If a question mentions strict SLA requirements or guaranteed replication time, RTC provides 99.99% of objects replicated within 15 minutes.
5. Encryption Scenarios:
- SSE-S3: Works with default settings
- SSE-KMS: Requires specifying the KMS key for the destination region
- SSE-C: Cannot be replicated
6. Same-Region vs Cross-Region: Know the difference. SRR (Same-Region Replication) keeps data in the same region; CRR copies to a different region. Choose based on the use case described.
7. IAM Role Requirement: S3 needs an IAM role with permissions to read from source and write to destination. If permissions issues are mentioned, check the IAM role configuration.
8. Cost Considerations: CRR incurs costs for storage in the destination bucket, data transfer between regions, and replication requests. Questions about cost optimization may involve choosing appropriate storage classes for replicas.
9. Bi-directional Replication: To achieve two-way replication, you must configure separate replication rules in both directions.
10. Disaster Recovery Scenarios: When questions describe DR requirements across regions, CRR is typically the answer. For compliance or latency scenarios, evaluate whether CRR or SRR is more appropriate.
Common Exam Scenarios:
• Scenario: Company needs to comply with regulations requiring data backup in a separate geographic location → Answer: Enable CRR
• Scenario: Need to replicate existing objects → Answer: Use S3 Batch Replication in addition to CRR
• Scenario: Replication is configured but objects are not replicating → Answer: Check if versioning is enabled on both buckets
• Scenario: Need guaranteed replication time → Answer: Enable Replication Time Control (RTC)
• Scenario: Deletes in source bucket should reflect in destination → Answer: Enable delete marker replication