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June 19, 2018 By Ben Newton

Log Management and Analytics for the AWS ELB Classic Service

Quick Refresher

Earlier this year, we showed you how to monitor Amazon Web Services Elastic Load Balancer (AWS ELB) with Cloudwatch. This piece is a follow up to that, and will focus on Classic Load Balancers. Classic Load Balancers provide basic load balancing across multiple Amazon EC2 instances and operate at both the request level and connection level. Classic Load Balancers are intended for applications that were built within the EC2-Classic network. AWS provides the ability to monitor your ELB configuration with detailed logs of all the requests made to your load balancers. There is a wealth of data in the logs generated by ELB, and it is extremely simple to set up.

How to Get Started: Setting up AWS ELB Logs

Logging is not enabled in AWS ELB by default. It is important to set up logging when you start using the service so you don’t miss any important details!

Step 1: Create an S3 Bucket and Enable ELB Logging

Note: If you have more than one AWS account (such as ops, dev, and so on) or multiple regions that generate Elastic Load Balancing data, you’ll probably need to configure each of these separately.

Here are the key steps you need to follow

  1. Create an S3 Bucket to store the logs

Note: Want to learn more about S3? Look no further (link)

  1. Allow AWS ELB access to the S3 Bucket
  2. Enable AWS ELB Logging in the AWS Console
  3. Verify that it is working

Step 2: Allow Access to external Log Management Tools

To add AWS ELB logs to your log management strategy, you need to give access to your log management tool! The easiest way to do that is by creating a special user and policy.

  1. Create a user in AWS Identity and Access Management (IAM) with Programmatic Access. For more information about this, refer to the appropriate section of the AWS User Guide.

Note: Make sure to store the Access Key ID and Secret Access Key credentials in a secure location. You will need to provide these later to provide access to your tools!

  1. Create a Custom Policy for the new IAM user. We recommend you use the following JSON policy:


Note: All of the Action parameters shown above are required. Replace the “your_bucketname” placeholders in the Resource section of the JSON policy with your actual S3 bucket name.

Refer to the Access Policies section of the AWS User Guide for more info.

What do the Logs look like?

ELB logs are stored as .log files in the S3 buckets you specify when you enable logging.

The file names of the access logs use the following format:



The name of the S3 bucket.


The prefix (logical hierarchy) in the bucket. If you don’t specify a prefix, the logs are placed at the root level of the bucket.


The AWS account ID of the owner.


The region for your load balancer and S3 bucket.


The date that the log was delivered.


The name of the load balancer.


The date and time that the logging interval ended. For example, an end time of 20140215T2340Z contains entries for requests made between 23:35 and 23:40 if the publishing interval is 5 minutes.


The IP address of the load balancer node that handled the request. For an internal load balancer, this is a private IP address.


A system-generated random string.

The following is an example log file name:



Each log entry contains the details of a single request made to the load balancer. All fields in the log entry are delimited by spaces. Each entry in the log file has the following format:

timestamp elb client:port backend:port request_processing_time backend_processing_time response_processing_time elb_status_code backend_status_code received_bytes sent_bytes “request” “user_agent” ssl_cipher ssl_protocol

The following table explains the different fields in the log file. Note: ELB can process HTTP requests and TCP requests, and the differences are noted below:

timestampThe time when the load balancer received the request from the client, in ISO 8601 format.
elbThe name of the load balancer
client:portThe IP address and port of the requesting client.
backend:portThe IP address and port of the registered instance that processed this request.
request_processing_time[HTTP listener] The total time elapsed, in seconds, from the time the load balancer received the request until the time it sent it to a registered instance.

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Ben Newton

Ben Newton

Ben is a veteran of the IT Operations market, with a two decade career across large and small companies like Loudcloud, BladeLogic, Northrop Grumman, EDS, and BMC. Ben got to do DevOps before DevOps was cool, working with government agencies and major commercial brands to be more agile and move faster. More recently, Ben spent 5 years in product management at Sumo Logic, and is now running product marketing for Operations Analytics at Sumo Logic. His latest project, Masters of Data, has let him combine his love of podcasts and music with his love of good conversations.

More posts by Ben Newton.

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