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Application Load Balancers

Access Logs for Your Application Load Balancer

Elastic Load Balancing provides access logs that capture detailed information about requests or connections sent to your load balancer. Each log contains information such as the time it was received, the client's IP address, latencies, request paths, and server responses. You can use these access logs to analyze traffic patterns and to troubleshoot issues.

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 and stores them in the Amazon S3 bucket that you specify as compressed files. You can disable access logging at any time.

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:

bucket[/prefix]/AWSLogs/aws-account-id/elasticloadbalancing/region/yyyy/mm/dd/aws-account-id_elasticloadbalancing_region_load-balancer-id_end-time_ip-address_random-string.log.gz
bucket

The name of the S3 bucket.

prefix

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.

aws-account-id

The AWS account ID of the owner.

region

The region for your load balancer and S3 bucket.

yyyy/mm/dd

The date that the log was delivered.

load-balancer-id

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

end-time

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.

ip-address

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

random-string

A system-generated random string.

The following is an example log file name:

s3://my-bucket/prefix/AWSLogs/123456789012/elasticloadbalancing/us-east-2/2016/05/01/123456789012_elasticloadbalancing_us-east-2_my-loadbalancer_20140215T2340Z_172.160.001.192_20sg8hgm.log.gz

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

Elastic Load Balancing logs requests sent to the load balancer, including requests that never made it to the targets. For example, if a client sends a malformed request, or there are no healthy targets to respond to the request, the request is still logged. Note that Elastic Load Balancing does not log health check requests.

For WebSockets, an entry is written only after the connection is closed. If the upgraded connection can't be established, the entry is the same as for an HTTP or HTTPS request.

Important

Elastic Load Balancing logs requests on a best-effort basis. We recommend that you use access logs to understand the nature of the requests, not as a complete accounting of all requests.

Syntax

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

type timestamp elb client:port target:port request_processing_time target_processing_time response_processing_time elb_status_code target_status_code received_bytes sent_bytes "request" "user_agent" ssl_cipher ssl_protocol target_group_arn trace_id

You should ignore any fields at the end of the log entry that you were not expecting.

The following table describes the fields of an access log entry.

Field Description

type

The type of request or connection. The possible values are as follows (ignore any other values):

  • http — HTTP

  • https — HTTP over SSL/TLS

  • h2 — HTTP/2 over SSL/TLS

  • ws — WebSockets

  • wss — WebSockets over SSL/TLS

timestamp

The time when the load balancer received the request from the client, in ISO 8601 format. For WebSockets, this is the time when the connection is closed.

elb

The resource ID of the load balancer. If you are parsing access log entries, note that resources IDs can contain forward slashes (/).

client:port

The IP address and port of the requesting client.

target:port

The IP address and port of the target that processed this request.

If the client didn't send a full request, the load balancer can't dispatch the request to a target, and this value is set to -.

request_processing_time

The total time elapsed, in seconds, from the time the load balancer received the request until the time it sent it to a target.

This value is set to -1 if the load balancer can't dispatch the request to a target. This can happen if the target closes the connection before the idle timeout or if the client sends a malformed request.

target_processing_time

The total time elapsed, in seconds, from the time the load balancer sent the request to a target until the target started to send the response headers.

This value is set to -1 if the load balancer can't dispatch the request to a target. This can happen if the target closes the connection before the idle timeout or if the client sends a malformed request.

response_processing_time

The total time elapsed (in seconds) from the time the load balancer received the response header from the target until it started to send the response to the client. This includes both the queuing time at the load balancer and the connection acquisition time from the load balancer to the target.

This value is set to -1 if the load balancer can't send the request to a target. This can happen if the target closes the connection before the idle timeout or if the client sends a malformed request.

elb_status_code

The status code of the response from the load balancer.

target_status_code

The status code of the response from the target. This value is recorded only if a connection was established to the target and the target sent a response. Otherwise, the value is set to -.

received_bytes

The size of the request, in bytes, received from the client (requester). For HTTP requests, this includes the headers. For WebSockets, this is the total number of bytes received from the client on the connection.

sent_bytes

The size of the response, in bytes, sent to the client (requester). For HTTP requests, this includes the headers. For WebSockets, this is the total number of bytes sent to the client on the connection.

request

The request line from the client enclosed in double quotes and logged using the following format: HTTP method + protocol://host:port/uri + HTTP version.

user_agent

A User-Agent string that identifies the client that originated the request. The string consists of one or more product identifiers, product[/version]. If the string is longer than 8 KB, it is truncated.

ssl_cipher

[HTTPS listener] The SSL cipher. This value is recorded only if the incoming connection was established after a successful negotiation. Otherwise, the value is set to -.

ssl_protocol

[HTTPS listener] The SSL protocol. This value is recorded only if the incoming connection was established after a successful negotiation. Otherwise, the value is set to -.

target_group_arn

The Amazon Resource Name (ARN) of the target group.

trace_id

The contents of the X-Amzn-Trace-Id header.

Examples

The following are example log entries. Note that the text appears on multiple lines only to make them easier to read.

Example HTTP Entry

The following is an example log entry for an HTTP listener (port 80 to port 80):

http 2016-08-10T22:08:42.945958Z app/my-loadbalancer/50dc6c495c0c9188 
192.168.131.39:2817 10.0.0.1:80 0.000 0.001 0.000 200 200 34 366 
"GET http://www.example.com:80/ HTTP/1.1" "curl/7.46.0" - - 
arn:aws:elasticloadbalancing:us-east-2:123456789012:targetgroup/my-targets/73e2d6bc24d8a067
"Root=1-58337262-36d228ad5d99923122bbe354"

Example HTTPS Entry

The following is an example log entry for an HTTPS listener (port 443 to port 80):

https 2016-08-10T23:39:43.065466Z app/my-loadbalancer/50dc6c495c0c9188 
192.168.131.39:2817 10.0.0.1:80 0.086 0.048 0.037 200 200 0 57 
"GET https://www.example.com:443/ HTTP/1.1" "curl/7.46.0" ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 
arn:aws:elasticloadbalancing:us-east-2:123456789012:targetgroup/my-targets/73e2d6bc24d8a067
"Root=1-58337281-1d84f3d73c47ec4e58577259"

Example HTTP/2 Entry

The following is an example log entry for an HTTP/2 stream.

h2 2016-08-10T00:10:33.145057Z app/my-loadbalancer/50dc6c495c0c9188 
10.0.1.252:48160 10.0.0.66:9000 0.000 0.002 0.000 200 200 5 257 
"GET https://10.0.2.105:773/ HTTP/2.0" "curl/7.46.0" ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2
arn:aws:elasticloadbalancing:us-east-2:123456789012:targetgroup/my-targets/73e2d6bc24d8a067
"Root=1-58337327-72bd00b0343d75b906739c42"

Example WebSockets Entry

The following is an example log entry for a WebSockets connection.

ws 2016-08-10T00:32:08.923954Z app/my-loadbalancer/50dc6c495c0c9188 
10.0.0.140:40914 10.0.1.192:8010 0.001 0.003 0.000 101 101 218 587 
"GET http://10.0.0.30:80/ HTTP/1.1" "-" - - 
arn:aws:elasticloadbalancing:us-east-2:123456789012:targetgroup/my-targets/73e2d6bc24d8a067
"Root=1-58337364-23a8c76965a2ef7629b185e3"

Example Secured WebSockets Entry

The following is an example log entry for a secured WebSockets connection.

wss 2016-08-10T00:42:46.423695Z app/my-loadbalancer/50dc6c495c0c9188 
10.0.0.140:44244 10.0.0.171:8010 0.000 0.001 0.000 101 101 218 786
"GET https://10.0.0.30:443/ HTTP/1.1" "-" ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 
arn:aws:elasticloadbalancing:us-west-2:123456789012:targetgroup/my-targets/73e2d6bc24d8a067
"Root=1-58337364-23a8c76965a2ef7629b185e3"

Bucket Permissions

When you enable access logging, you must specify an S3 bucket for the access logs. This bucket must be located in the same region as the load balancer, and must have a bucket policy that grants Elastic Load Balancing 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. Each statement includes information about a single permission and contains a series of elements.

Important

If you will use the console to enable access logging, you can skip to Enable Access Logging. If you will use the AWS CLI or an API to enable access logging, the bucket must exist and must have the required bucket policy.

If you need to create a bucket for your access logs, use the following procedure to create the bucket and add the required bucket policy. If you already have a bucket, start at step 4 to add or update the bucket policy for your bucket.

To create an Amazon S3 bucket with the required permissions

  1. Open the Amazon S3 console at https://console.aws.amazon.com/s3/.

  2. Choose Create Bucket.

  3. In the Create a Bucket dialog box, do the following:

    1. For Bucket Name, enter a name for your bucket (for example, my-loadbalancer-logs). This name must be unique across all existing bucket names in Amazon S3. In some regions, there might be additional restrictions on bucket names. For more information, see Bucket Restrictions and Limitations in the Amazon Simple Storage Service Developer Guide.

    2. For Region, select the region where you created your load balancer.

    3. Choose Create.

  4. Select the bucket and choose Properties.

  5. For Permissions, choose Add bucket policy. If your bucket already has an attached policy, choose Edit bucket policy. You can add the required statement to the existing policy.

  6. In the Bucket Policy Editor dialog box, choose AWS Policy Generator.

  7. In the AWS Policy Generator dialog box, do the following:

    1. For Select Type of Policy, choose S3 Bucket Policy.

    2. For Effect, choose Allow.

    3. For Principal, specify one of the following AWS account IDs to grant Elastic Load Balancing access to the S3 bucket. Use the account ID that corresponds to the region for your load balancer and bucket.

      Region Region Name Elastic Load Balancing Account ID
      us-east-1 US East (N. Virginia) 127311923021
      us-east-2 US East (Ohio) 033677994240
      us-west-1 US West (N. California) 027434742980
      us-west-2 US West (Oregon) 797873946194
      ca-central-1 Canada (Central) 985666609251
      eu-west-1 EU (Ireland) 156460612806
      eu-central-1 EU (Frankfurt) 054676820928
      eu-west-2 EU (London) 652711504416
      ap-northeast-1 Asia Pacific (Tokyo) 582318560864
      ap-northeast-2 Asia Pacific (Seoul) 600734575887
      ap-southeast-1 Asia Pacific (Singapore) 114774131450
      ap-southeast-2 Asia Pacific (Sydney) 783225319266
      ap-south-1 Asia Pacific (Mumbai) 718504428378
      sa-east-1 South America (São Paulo) 507241528517
      us-gov-west-1* AWS GovCloud (US) 048591011584
      cn-north-1* China (Beijing) 638102146993

      * These regions requires a separate account. For more information, see AWS GovCloud (US) and China (Beijing).

    4. For Actions, choose PutObject to allow Elastic Load Balancing to store objects in the S3 bucket.

    5. For Amazon Resource Name (ARN), enter the ARN of your S3 bucket in the following format. For aws-account-id, specify the ID of the AWS account that owns the load balancer (for example, 123456789012).

      arn:aws:s3:::bucket/prefix/AWSLogs/aws-account-id/*

      Note that if you are using the us-gov-west-1 region, specify arn:aws-us-gov instead of arn:aws in the ARN.

    6. Choose Add Statement, Generate Policy. The policy document should be similar to the following:

      {
        "Id": "Policy1429136655940",
        "Version": "2012-10-17",
        "Statement": [
          {
            "Sid": "Stmt1429136633762",
            "Action": [
              "s3:PutObject"
            ],
            "Effect": "Allow",
            "Resource": "arn:aws:s3:::my-loadbalancer-logs/my-app/AWSLogs/123456789012/*",
            "Principal": {
              "AWS": [
                "797873946194"
              ]
            }
          }
        ]
      }
    7. If you are creating a new bucket policy, copy the entire policy document, and then choose Close. Go back to the Bucket Policy Editor dialog box, paste the policy into the text area, and then choose Save.

      If you are editing an existing bucket policy, copy the new statement from the policy document (the text between the [ and ] of the Statement element), and then choose Close. Go back to the Bucket Policy Editor dialog box, paste the statement in the Statement element (making sure to separate the new statement from the existing statements using a comma), and then choose Save.

  8. Under Permissions, choose Save.

Enable 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. The bucket must be in the same region as your load balancer, and must have a bucket policy that grants Elastic Load Balancing permission to write the access logs to the bucket. The bucket can be owned by a different account than the account that owns the load balancer.

To enable 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.

    3. (Optional) If the bucket does not exist, choose Create this location for me. You must specify a name that is unique across all existing bucket names in Amazon S3 and follows the DNS naming conventions. For more information, see Rules for Bucket Naming in the Amazon Simple Storage Service Developer Guide.

    4. Choose Save.

To enable access logging using the AWS CLI

Use the modify-load-balancer-attributes command.

To verify that Elastic Load Balancing created a test file in your S3 bucket

After access logging is enabled for your load balancer, Elastic Load Balancing validates the S3 bucket and creates a test file to ensure that the bucket policy specifies the required permissions. You can use the Amazon S3 console to verify that the test file was created. Note that the test file is not an actual access log file; it doesn't contain example records.

  1. Open the Amazon S3 console at https://console.aws.amazon.com/s3/.

  2. For All Buckets, select your S3 bucket.

  3. Navigate to the test log file. The path should be as follows:

    my-bucket/prefix/AWSLogs/123456789012/ELBAccessLogTestFile

Disable Access Logging

You can disable access logging for your load balancer at any time. After you disable access logging, your access logs remain in your S3 bucket until you delete the them. For more information, see Working with Buckets in the Amazon Simple Storage Service Console User Guide.

To 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, clear Enable access logs.

  6. Choose Save.

To disable 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: