Elastic Load Balancing
Network Load Balancers

Access Logs for Your Network Load Balancer

Elastic Load Balancing provides access logs that capture detailed information about the TLS requests sent to your Network Load Balancer. You can use these access logs to analyze traffic patterns and troubleshoot issues.


Access logs are created only if the load balancer has a TLS listener and they contain information only about TLS requests.

Access logging is an optional feature of Elastic Load Balancing that is disabled by default. After you enable access logging for your load balancer, Elastic Load Balancing captures the logs as compressed files and stores them in the Amazon S3 bucket that you specify. You can disable access logging at any time.

If you enable server-side encryption with Amazon S3-managed encryption keys (SSE-S3) for your S3 bucket, each access log file is automatically encrypted before it is stored in your S3 bucket and decrypted when you access it. You do not need to take any action as there is no difference in the way you access encrypted or unencrypted log files. Each log file is encrypted with a unique key, which is itself encrypted with a master key that is regularly rotated. For more information, see Protecting Data Using Server-Side Encryption with Amazon S3-Managed Encryption Keys (SSE-S3) in the Amazon Simple Storage Service Developer Guide.

There is no additional charge for access logs. You are charged storage costs for Amazon S3, but not charged for the bandwidth used by Elastic Load Balancing to send log files to Amazon S3. For more information about storage costs, see Amazon S3 Pricing.

Access Log Files

Elastic Load Balancing publishes a log file for each load balancer node every 5 minutes. Log delivery is eventually consistent. The load balancer can deliver multiple logs for the same period. This usually happens if the site has high traffic.

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 resource ID of the load balancer. If the resource ID contains any forward slashes (/), they are replaced with periods (.).


The date and time that the logging interval ended. For example, an end time of 20181220T2340Z contains entries for requests made between 23:35 and 23:40.


A system-generated random string.

You can store your log files in your bucket for as long as you want, but you can also define Amazon S3 lifecycle rules to archive or delete log files automatically. For more information, see Object Lifecycle Management in the Amazon Simple Storage Service Developer Guide.

Access Log Entries

The following table describes the fields of an access log entry, in order. All fields are delimited by spaces. When new fields are introduced, they are added to the end of the log entry. When processing the log files, you should ignore any fields at the end of the log entry that you were not expecting.

Field Description


The type of listener. The supported value is tls.


The version of the log entry. The supported version is 1.0.


The timestamp recorded at the end of the TLS connection, in ISO 8601 format.


The resource ID of the load balancer.


The resource ID of the TLS listener for the connection.


The IP address and port of the client.


The IP address and port of the listener.


The total time for the connection to complete, from start to closure, in milliseconds.


The total time for the TLS handshake to complete after the TCP connection is established, including client-side delays, in milliseconds. This time is included in the connection_time field.


The count of bytes received by the load balancer from the client, after decryption.


The count of bytes sent by the load balancer to the client, before encryption.


The integer value of TLS alerts received by the load balancer from the client, if present. Otherwise, this value is set to -.


The ARN of the certificate served to the client. If no valid client hello message is sent, this value is set to -.


Reserved for future use. This value is always set to -.


The cipher suite negotiated with the client, in OpenSSL format. If TLS negotiation does not complete, this value is set to -.


The TLS protocol negotiated with the client, in string format. The possible values are tlsv10, tlsv11, and tlsv12. If TLS negotiation does not complete, this value is set to -.


Reserved for future use. This value is always set to -.


The value of the server_name extension in the client hello message. This value is URL-encoded. If no valid client hello message is sent or the extension is not present, this value is set to -.

Example Log Entry

The following is an example log entry. Note that the text appears on multiple lines only to make it easier to read.

tls 1.0 2018-12-20T02:59:40 net/my-network-loadbalancer/c6e77e28c25b2234 g3d4b5e8bb8464cd 5 2 98 246 - arn:aws:acm:us-east-2:671290407336:certificate/2a108f19-aded-46b0-8493-c63eb1ef4a99 - ECDHE-RSA-AES128-SHA tlsv12 - my-network-loadbalancer-c6e77e28c25b2234.elb.us-east-2.amazonaws.com

Bucket Requirements

When you enable access logging, you must specify an S3 bucket for the access logs. The bucket can be owned by a different account than the account that owns the load balancer. The bucket must meet the following requirements.


  • The bucket must be located in the same region as the load balancer.

  • The bucket must have a bucket policy that grants permission to write the access logs to your bucket. Bucket policies are a collection of JSON statements written in the access policy language to define access permissions for your bucket. The following is an example policy.

    { "Version": "2012-10-17", "Statement": [ { "Sid": "AWSLogDeliveryWrite", "Effect": "Allow", "Principal": { "Service": [ "delivery.logs.amazonaws.com" ] }, "Action": [ "s3:PutObject" ], "Resource": "arn:aws:s3:::bucket_name/prefix/AWSLogs/123456789012/*", "Condition": {"StringEquals": {"s3:x-amz-acl": "bucket-owner-full-control"}} }, { "Sid": "AWSLogDeliveryAclCheck", "Effect": "Allow", "Principal": { "Service": [ "delivery.logs.amazonaws.com" ] }, "Action": [ "s3:GetBucketAcl" ], "Resource": "arn:aws:s3:::bucket_name" } ] }

Enable or Disable Access Logging

When you enable access logging for your load balancer, you must specify the name of the S3 bucket where the load balancer will store the logs. For more information, see Bucket Requirements.

To enable or disable access logging using the console

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. In the navigation pane, choose Load Balancers.

  3. Select your load balancer.

  4. On the Description tab, choose Edit attributes.

  5. On the Edit load balancer attributes page, do the following:

    1. Choose Enable access logs.

    2. For S3 location, type the name of your S3 bucket, including any prefix (for example, my-loadbalancer-logs/my-app). You can specify the name of an existing bucket or a name for a new bucket. If you specify an existing bucket, be sure that you own this bucket and that you configured the required bucket policy.

    3. Choose Save.

To enable access logging using the AWS CLI

Use the modify-load-balancer-attributes command.

Processing Access Log Files

The access log files are compressed. If you open the files using the Amazon S3 console, they are uncompressed and the information is displayed. If you download the files, you must uncompress them to view the information.

If there is a lot of demand on your website, your load balancer can generate log files with gigabytes of data. You might not be able to process such a large amount of data using line-by-line processing. Therefore, you might have to use analytical tools that provide parallel processing solutions. For example, you can use the following analytical tools to analyze and process access logs: