ELB (Elastic Load Balancer) access logs are a crucial monitoring feature that captures detailed information about requests sent to your load balancer. These logs are essential for troubleshooting, analyzing traffic patterns, and maintaining security compliance in AWS environments.
When enabled, EL…ELB (Elastic Load Balancer) access logs are a crucial monitoring feature that captures detailed information about requests sent to your load balancer. These logs are essential for troubleshooting, analyzing traffic patterns, and maintaining security compliance in AWS environments.
When enabled, ELB access logs record comprehensive data including client IP addresses, latencies, request paths, server responses, timestamps, and backend instance information. Each log entry contains fields such as the request processing time, backend processing time, response processing time, ELB status code, and backend status code.
Access logs are stored in Amazon S3 buckets that you specify during configuration. AWS delivers these logs at intervals of 5 minutes for Application Load Balancers (ALB) and 60 minutes for Classic Load Balancers. The logs are compressed and stored in a structured format, making them suitable for analysis using tools like Amazon Athena, AWS Glue, or third-party solutions.
To enable access logs, you must configure the S3 bucket with appropriate permissions, allowing the ELB service to write log files. The bucket policy must grant write access to the Elastic Load Balancing service principal. Additionally, server-side encryption can be applied to protect log data at rest.
Key use cases for ELB access logs include identifying slow-performing backend instances, detecting unusual traffic patterns that might indicate security threats, analyzing user behavior and geographic distribution, and debugging application errors based on HTTP status codes.
For the SysOps Administrator exam, understanding how to enable, configure, and analyze these logs is essential. You should know the differences between ALB and Classic Load Balancer logging capabilities, S3 bucket requirements, log format fields, and integration with other AWS services for log analysis. Access logs complement CloudWatch metrics by providing request-level visibility rather than aggregated statistics, enabling deeper troubleshooting capabilities for production workloads.
ELB Access Logs are a feature that captures detailed information about requests sent to your Elastic Load Balancer. These logs contain data such as the time the request was received, the client's IP address, latencies, request paths, and server responses. Access logs are stored in Amazon S3 buckets that you specify.
Why are ELB Access Logs Important?
• Security Analysis: Track and identify suspicious traffic patterns or potential attacks • Troubleshooting: Diagnose connectivity issues and understand request flow • Compliance: Meet regulatory requirements for logging and auditing • Performance Monitoring: Analyze latency patterns and identify bottlenecks • Traffic Analysis: Understand user behavior and traffic patterns
How ELB Access Logs Work
1. Enable Access Logging: Configure access logging on your load balancer through the AWS Console, CLI, or API
2. Specify S3 Bucket: Provide an S3 bucket where logs will be stored. The bucket must have the proper bucket policy allowing ELB to write logs
3. Log Generation: ELB publishes log files to your S3 bucket at intervals (every 5 minutes for ALB/NLB, every 5-60 minutes for CLB)
4. Log Format: Each log entry contains fields including timestamp, ELB name, client IP/port, target IP/port, request processing time, response code, and more
Key Configuration Steps
• Create an S3 bucket in the same region as your load balancer • Attach a bucket policy that grants ELB service principal write permissions • Enable access logging on the load balancer and specify the S3 bucket and optional prefix • Logs are stored as compressed files (.gz format)
Important Details to Remember
• Access logging is disabled by default - you must enable it • There is no additional charge for access logs - you only pay for S3 storage • Logs are delivered on a best-effort basis • ALB and NLB logs have different formats than CLB logs • The S3 bucket must be in the same region as the load balancer
Exam Tips: Answering Questions on ELB Access Logs
• When asked about troubleshooting ELB issues: Access logs help identify client IPs, error codes, and latency problems
• When asked about security and auditing: Access logs provide the audit trail needed for compliance and security analysis
• When asked about log storage: Remember logs go to S3, not CloudWatch Logs (CloudWatch is for metrics)
• When asked about bucket permissions: The S3 bucket needs a specific bucket policy allowing the ELB service to write logs
• When asked about costs: Access logging itself is free; you pay for S3 storage costs
• When asked about default behavior: Access logging is NOT enabled by default
• When asked about log delivery: Logs are delivered on a best-effort basis and may have delays
• When asked about cross-region: The S3 bucket must be in the same region as the ELB
• When asked about analyzing logs: You can use Amazon Athena to query access logs stored in S3
Common Exam Scenarios
• Scenario requiring tracking of client IP addresses → Enable access logs • Scenario needing to analyze historical traffic patterns → Use access logs with Athena • Scenario about compliance requirements → Access logs provide necessary audit trails • Scenario about identifying slow backend targets → Access logs contain target response times