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Amazon S3 server access logging captures detailed records for every request to a bucket, enabling you to audit access, debug issues, and optimize storage. Each operation—such as a GET on file1.txt—generates a log entry that records who accessed the object, when the request occurred, and which API call was performed: 
John [06/Feb/2019:00:00:38 +0000] GET /file1.txt

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Why Enable Access Logs?

Enabling server access logging provides several advantages:
BenefitDescription
Security & AuditingTrack who accessed objects and when, supporting compliance requirements.
Usage PatternsAnalyze request frequency to select the most cost-effective storage class.
Centralized Log StorageCollect logs in a dedicated bucket for easy management and analysis.
Storing and analyzing access logs may incur additional storage and request charges. Review your AWS billing dashboard to estimate costs.

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What Information Is Logged?

Each log record consists of numerous fields, including:
FieldDescription
Bucket ownerAWS account ID of the bucket owner
Bucket nameName of the S3 bucket
TimestampDate and time of the request (in UTC)
Requester IP & IDClient IP address and AWS user identifier (or - if anonymous)
Request IDUnique ID assigned by S3 for the request
OperationAPI action (e.g., REST.GET.OBJECT, REST.PUT.OBJECT)
Object key & VersionRequested object path and version ID
HTTP status & ErrorHTTP response code and any error codes
Bytes sent & ReceivedPayload sizes in bytes and response timing
User agentClient application or browser details
For the complete list of log fields, see Monitoring Amazon S3 > Log Format in the AWS documentation:
The image shows a webpage from the Amazon Simple Storage Service (S3) documentation, detailing server access log formats and examples. It includes sections on HTTP status, error codes, bytes sent, object size, total time, and turn-around time.

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Sample Log Entry

A typical S3 access log record begins with the bucket owner and bucket name, followed by the timestamp and requester details: 
1e69f8cfa4d16e09c88f48d218e7c47fe2be DOC-EXAMPLE-BUCKET1 [06/Feb/2019:00:00:38 +0000] 192.0.2.3 79d59f4b900b49e95d5e1a69f8f8c49c8e9e09b0c8af8d218e7c47fe2be 3571 0 0
Subsequent fields describe the operation, request line, status, bytes, and user agent: 
b0a88ac8fa921b2c7dfe 3E74277EXAMPLE REST.GET.VERSIONING "GET /DOC-EXAMPLE-BUCKET17/versioning HTTP/1.1" 200 113 "-" "$3Console/0.4" s9i2nYFfP76zVrKcP9<5
b0a88ac8fa921b2c7dfe 89C12E74EXAMPLE REST.GET.LOGGING_STATUS "GET /DOC-EXAMPLE-BUCKET17/logging HTTP/1.1" 200 242 11 "-" "$3Console/0.4" -9xkBeVhWfNxiM2bLxmOk0xq
b0a88ac8fa921b2c7dfe A2401f406E12 REST.GET.BUCKETPOLICY "GET /DOC-EXAMPLE-BUCKET17/policy HTTP/1.1" 404 NoSuchBucketPolicy 29 "-" "$3Console/0.4" -bMBSx0xqo
b0a88ac8fa921b2c7dfe REST.PUT.OBJECT s3-dg.pdf "PUT /DOC-EXAMPLE-BUCKET17/s3-dg.pdf HTTP/1.1" 200 - 28 "-" "$3Console/0.4" 160621Z1v8K1v8
All generated log files are delivered as plain text to your designated logging bucket:
The image shows a webpage from the AWS documentation about Amazon S3 server access log format, detailing log record fields and providing an example of log records.

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