S3 Replication — CRR and SRR

S3 Replication — Copy Objects Across Buckets

S3 Replication automatically copies objects from one S3 bucket to another. You configure replication rules and AWS handles the copying asynchronously in the background.

Cross-Region Replication (CRR)

CRR copies objects to a bucket in a DIFFERENT AWS region. Use cases:

• Disaster Recovery: have a copy in another region if primary region fails
• Data Sovereignty: keep EU data in EU, replicate for analytics to us-east-1
• Reduced latency: replicate data closer to users in different regions
• Legal requirement: some regulations require geographic data distribution

Same-Region Replication (SRR)

SRR copies objects within the SAME AWS region. Use cases:

• Log aggregation: copy logs from multiple source buckets to one central audit bucket
• Development: replicate production data to dev environment bucket
• Account separation: copy data between accounts while keeping in same region

Replication Requirements

• Versioning must be enabled on BOTH source and destination buckets
• Replication copies NEW objects going forward — does NOT retroactively replicate existing objects
• To replicate existing objects: use S3 Batch Replication or run aws s3 sync
• Delete markers are not replicated by default (can be enabled)
• Replication is asynchronous — small replication lag (usually seconds to minutes)

# Enable replication via CLI
aws s3api put-bucket-replication 
  --bucket source-bucket 
  --replication-configuration file://replication.json

# replication.json
{
  "Role": "arn:aws:iam::...:role/S3ReplicationRole",
  "Rules": [{
    "Status": "Enabled",
    "Filter": {"Prefix": "important/"},
    "Destination": {
      "Bucket": "arn:aws:s3:::destination-bucket",
      "StorageClass": "STANDARD_IA"
    }
  }]
}