Help Center/ Elastic Load Balance/ User Guide/ User Guide for Dedicated Load Balancers/ Enabling Access Logging for Your Load Balancer
Updated on 2025-09-25 GMT+08:00
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Enabling Access Logging for Your Load Balancer

When you use HTTP/HTTPS listeners of a load balancer to route requests, if there is an unhealthy backend server, it is challenging to quickly locate the root cause by checking the logs of this backend server.

Log Tank Service (LTS) can log Layer 7 requests, of a load balancer including the time when the request was sent, client IP address, request path, server response, and more. If there are service faults or exceptions caused by unhealthy backend servers, you can view logs of requests to load balancers and analyze response status codes to quickly locate unhealthy backend servers.

Operations data, such as access logs, of ELB is on the LTS console. Do not transmit private or sensitive data through fields in access logs. Encrypt your sensitive data if necessary.

What Is ELB Access Logging?

ELB receives and distributes client access requests. It logs the details of Layer 7 requests. With LTS, you can quickly analyze service requests and locate faults.

The following information is logged:

  • Time information: Fields such as msec and time_iso8601 record the time when requests were sent. They are used for analyzing time sequence and locating faults.
  • Basic client request information: Fields such as remote_addr:remote_port, request_method scheme://host request_uri server_protocol, and http_user_agent record basic request information, which is used for user analysis and security audit.
  • Request response and performance metrics: Fields such as status, bytes_sent, and request_time record response status and processing time, which are used for locating request status and monitoring performance.
  • Load balancer information: Fields such as lb_name, listener_id, pool_name, and eip_address:eip_port record the details of load balancers that are used to route requests. They are used to identify the resource configuration and improve O&M efficiency.
  • Backend server information: Fields such as upstream_status, upstream_connect_time, and upstream_addr_priv record the information returned by backend servers and their configurations. They are used to identify the health status and performance of the backend servers.
  • HTTPS information: Fields such as ssl_protocol, sni_domain_name, and certificate_id record the HTTPS information for troubleshooting HTTPS requests.
  • Other information: Fields such as access_log_topic_id, log_ver, and tenant_id record the system and log IDs for log management.

Constraints

  • Access logging can be configured only for load balancers with HTTP or HTTPS listeners.
  • The access logs do not contain requests whose return code is 400 Bad Request. This is because such requests do not comply with HTTP specification and cannot be processed properly.

Preparations

  • Create a load balancer that supports HTTP and HTTPS.
  • Enable LTS.
  • Create a backend server group, add backend servers to the group, and deploy services on the backend servers. For details, see Creating a Backend Server Group.
  • Add an HTTP or HTTPS listener to the load balancer.

Configuring Access Logging

  1. Go to the load balancer list page.
  2. On the Load Balancers page, locate the load balancer and click its name.
  3. Under Access Logs, click Configure Access Logging.
  4. Enable access logging and select the log group and log stream you have created.

    If there are no log groups and log streams, you can create them on the ELB console.

    Creating a Log Group and Log Stream

    1. Click Create Log Group and Log Stream.
    2. In the Create Log Group and Log Stream dialog box, configure the log group name, log stream name, and log retention period.
    3. Click OK.
  5. Click OK.

Viewing Access Logs

You can view details about access logs on the:

  • ELB console: Go to the Access Logs tab of the target load balancer to view access logs.
  • (Recommended) LTS console: Locate the target log group and click its name. On the displayed page, locate the target log stream and click Real-Time Logs tab.

The log format is as follows, which cannot be modified:

$msec $access_log_topic_id [$time_iso8601] $log_ver $remote_addr:$remote_port $status "$request_method $scheme://$host$router_request_uri $server_protocol" $request_length $bytes_sent $body_bytes_sent $request_time "$upstream_status" "$upstream_connect_time" "$upstream_header_time" "$upstream_response_time" "$upstream_addr" "$http_user_agent" "$http_referer" "$http_x_forwarded_for" $lb_name $listener_name $listener_id
$pool_name "$member_name" $tenant_id $eip_address:$eip_port "$upstream_addr_priv" $certificate_id $ssl_protocol $ssl_cipher $sni_domain_name $tcpinfo_rtt $self_defined_header $request_header_length $actions_executed $error_reason "$pool_usr_name"

The following is a log example:

1644819836.370 eb11c5a9-93a7-4c48-80fc-03f61f638595 [2024-02-14T14:23:56+08:00] elb_01 192.168.1.1:888 200 "POST https://www.test.com/example/ HTTP/1.1" 1411 251 3 0.011 "200" "0.000" "0.011" "0.011" "192.168.1.2:8080" "okhttp/3.13.1" "-" "-" loadbalancer_295a7eee-9999-46ed-9fad-32a62ff0a687 listener_20679192-8888-4e62-a814-a2f870f62148 3333fd44fe3b42cbaa1dc2c641994d90 pool_89547549-6666-446e-9dbc-e3a551034c46 "-" f2bc165ad9b4483a9b17762da851bbbb 121.64.212.1:443 "10.1.1.2:8080" - TLSv1.2 ECDHE-RSA-AES256-GCM-SHA384 www.test.com 56704 "-" 129 waf - "My backend server group"

Log analysis:

At 14:23:56 GMT+08:00 on Feb 14, 2024, the load balancer received an HTTP/1.1 POST request from a client whose IP address and port number are 192.168.1.1 and 888, then routed the request to a backend server whose IP address and port number are 100.64.0.129 and 8080, and finally returned 200 OK to the client after receiving the status code from the backend server.

Log analysis result:

The backend server responds to the request normally.

Table 1 describes the fields in the log.

Table 1 ELB log fields

Parameter

Description

Value Description

Example Value

msec

Time when the log is written, in seconds with a milliseconds resolution.

Floating-point data

1644819836.370

access_log_topic_id

Log stream ID.

uuid

eb11c5a9-93a7-4c48-80fc-03f61f638595

time_iso8601

Local time in the ISO 8601 standard format.

N/A

[2024-02-14T14:23:56+08:00]

log_ver

Log format version.

Fixed value: elb_01

elb_01

remote_addr: remote_port

IP address and port number of the client.

Records the IP address and port of the client.

192.168.1.1:888

status

HTTP status code.

Records the request status code.

200

request_method scheme://host request_uri server_protocol

Request method Protocol://Host name: Request URI Request protocol
  • request_method: request method
  • scheme: HTTP or HTTPS
  • host: host name, which can be a domain name or an IP address
  • request_uri:

    indicates the native URI initiated by the browser without any modification and it does not include the protocol and host name.

"POST https://www.test.com/example/ HTTP/1.1"

request_length

Length of the request received from the client, including the header and body.

Integer

1411

bytes_sent

Number of bytes sent to the client.

Integer

251

body_bytes_sent

Number of bytes sent to the client (excluding the response header).

Integer

3

request_time

Request processing time in seconds from the time when the load balancer receives the first request packet from the client to the time when the load balancer sends the response packet.

Floating-point data

0.011

upstream_status

Response status code returned by the backend server.

  • When the load balancer attempts to retry a request, there will be multiple response status codes.
  • If the request is not correctly routed to the backend server, a hyphen (-) is displayed as a null value for this field.

HTTP status code returned by the backend server to the load balancer

"200"

upstream_connect_time

Time taken to establish a connection with the server, in seconds, with a milliseconds resolution.

  • When the load balancer attempts to retry a request, there will be multiple connection times.
  • If the request is not correctly routed to the backend server, a hyphen (-) is displayed as a null value for this field.

Floating-point data

"0.000"

upstream_header_time

Time taken to receive the response header from the server, in seconds, with a milliseconds resolution.

  • When the load balancer attempts to retry a request, there will be multiple response times.
  • If the request is not correctly routed to the backend server, a hyphen (-) is displayed as a null value for this field.

Floating-point data

"0.011"

upstream_response_time

Time taken to receive the response from the server, in seconds, with a milliseconds resolution.

  • When the load balancer attempts to retry a request, there will be multiple response times.
  • If the request is not correctly routed to the backend server, a hyphen (-) is displayed as a null value for this field.

Floating-point data

"0.011"

upstream_addr

IP address and port number of the backend server. There may be multiple values separated by commas and spaces, and each value is in the format of {IP address}:{Port number} or -.

IP address and port number

"192.168.1.2:8080"

http_user_agent

http_user_agent in the request header received by the load balancer, indicating the system model and browser information of the client.

Records the browser-related information.

"okhttp/3.13.1"

http_referer

http_referer in the request header received by the load balancer, indicating the page link of the request.

Request for a page link

"-"

http_x_forwarded_for

http_x_forwarded_for in the request header received by the load balancer, indicating the IP address of the proxy server that the request passes through.

IP address

"-"

lb_name

Load balancer name in the format of loadbalancer_load balancer ID

String

loadbalancer_295a7eee-9999-46ed-9fad-32a62ff0a687

listener_name

Listener name in the format of listener_listener ID.

String

listener_20679192-8888-4e62-a814-a2f870f62148

listener_id

ID of the listener added to the load balancer.

String

3333fd44fe3b42cbaa1dc2c641994d90

pool_name

Backend server group name in the format of pool_backend server group ID or pool_backend server group ID*load balancer ID.

String

pool_89547549-6666-446e-9dbc-e3a551034c46

member_name

Backend server name in the format of member_server ID. This field is not supported yet. There may be multiple values separated by commas and spaces, and each value is a member ID (member_id) or -.

String

"-"

tenant_id

Tenant ID.

String

f2bc165ad9b4483a9b17762da851bbbb

eip_address:eip_port

EIP of the load balancer and frontend port that were set when the listener was added.

EIP of the load balancer and frontend port that were set when the listener was added.

121.64.212.1:443

upstream_addr_priv

IP address and port number of the backend server. There may be multiple values separated by commas and spaces, and each value is in the format of {IP address}:{Port number} or -.

IP address and port number

"-" (Dedicated load balancers)

certificate_id

HTTPS listener: Certificate ID used for establishing an SSL connection. This field is not supported yet.

String

N/A

ssl_protocol

HTTPS listener: Protocol used for establishing an SSL connection. For a non-HTTPS listener, a hyphen (-) is displayed as a null value for this field.

String

TLSv1.2

ssl_cipher

HTTPS listener: Cipher suite used for establishing an SSL connection. For a non-HTTPS listener, a hyphen (-) is displayed as a null value for this field.

String

ECDHE-RSA-AES256-GCM-SHA384

sni_domain_name

HTTPS listener: SNI domain name provided by the client during SSL handshakes. For a non-HTTPS listener, a hyphen (-) is displayed as a null value for this field.

String

www.test.com

tcpinfo_rtt

TCP Round Trip Time (RTT) between the load balancer and client in microseconds.

Integer

56704

self_defined_header

This field is reserved. The default value is -.

String

"-"

request_header_length

The size of the header in the client request.

Integer

129

actions_executed

The WAF execution result.

String

  • waf: Requesting WAF succeeded.
  • waf-failed: Requesting WAF failed.
  • waf-block: The request is blocked by WAF.

waf

error_reason

Reason why requesting WAF fails.

String

  • WAFUnhandledException: Internal error. Contact the WAF service personnel to locate the fault.
  • WAFRequestHeaderLengthExceeded: The client request header length exceeds the upper limit.
  • WAFRequestBodyLengthExceeded: The client body is too large.
  • WAFRequestHeaderContentLengthEmpty: The body length of the client's request header is 0.
  • WAFResponseBodyReadError: Failed to read the body returned by WAF.
  • WAFResponseReadTimeout: Reading the result returned by WAF times out.
  • WAFConnectionTimeout: Connecting to WAF times out.
  • WAFConnectionError: Failed to connect to WAF.
  • WAFNoBackendAvailable: No backend server is available for WAF.
  • WAFNoBackendOnline: No backend server is online for WAF.

N/A

Locating an Unhealthy Backend Server

The following is a log that records an exception:

1554944564.344 - [2024-04-11T09:02:44+08:00] elb 10.133.251.171:51527 500 "GET http://10.154.73.58/lrange/guestbook HTTP/1.1" 411 3726 3545 19.028 "500" "0.009" "19.028" "19.028" "172.17.0.82:3000" "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.103 Safari/537.36" "http://10.154.73.58:5971/" "-" loadbalancer_ed0f790b-e194-4657-9f97-53426227099e listener_b21dd0a9-690a-4945-950e-b134095c6bd9 6b6aaf84d72b40fcb2d2b9b28f6a0b83

Log analysis

At 09:02:44 GMT+08:00 of April 11, 2024, the load balancer received a GET/HTTP/1.1 request from the client whose IP address and port number are 10.133.251.171 and 51527 respectively and then routed the request to a backend server that uses 172.17.0.82 and port 3000 to receive requests. The load balancer then received 500 Internal Server Error from the backend server and returned the status code to the client.

Analysis results

The backend server (private IP address: 172.17.0.82; port: 3000) was unhealthy and failed to respond to the request.

Parent Topic: User Guide for Dedicated Load Balancers