Access Logging

Scenarios

ELB logs HTTP and HTTPS requests received by shared load balancers, including the time when the request was sent, client IP address, request path, and server response.

With Log Tank Service (LTS), you can view logs of requests to load balancers at Layer 7 and analyze response status codes to quickly locate unhealthy backend servers.

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

Constraints

Access logging can be configured only for shared load balancers that have 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.

Prerequisites

You have created an application load balancer. For details, see Creating a Shared Load Balancer.
You have enabled LTS. For details, see Accessing LTS.
You have created a backend server group, added backend servers to the group, and deployed services on the backend servers. For details, see Creating a Backend Server Group.

You have added an HTTP or HTTPS listener to the load balancer. For details, see Adding an HTTP Listener or Adding an HTTPS Listener.

Flowchart

Figure 1 Process for locating an unhealthy backend server

Creating a Log Group

Log in to the management console.
In the upper left corner of the page, click and select the desired region and project.
Click in the upper left corner and choose Management & Governance > Log Tank Service.
In the navigation pane on the left, choose Log Management.
On the lower part of the displayed page, click Create Log Group. In the displayed dialog box, enter a name for the log group.
Figure 2 Creating a log group
Confirm the settings and click OK.

Creating a Log Stream

On the LTS console, click on the left of the target log group.
Click Create Log Stream. In the displayed dialog box, enter a name for the log stream.
Figure 3 Creating a log stream
Confirm the settings and click OK.

Configuring Access Logging

Click in the upper left corner to display Service List and choose Networking > Elastic Load Balance.
On the Load Balancers page, locate the load balancer and click its name.
Under Access Logs, click Configure Access Logging.
Enable access logging and select the log group and log stream you have created.
Figure 4 Configuring access logging
Click OK.

Ensure that the log group is in the same region as the load balancer.

Viewing Access Logs

You can view details about access logs on the:

ELB console: Click the name of the load balancer and click Access Logs to view 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

The following is a log example:

1644819836.370 eb11c5a9-93a7-4c48-80fc-03f61f638595 [2022-02-14T14:23:56+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" "100.64.0.129:8080" "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 -

Table 1 describes the fields in the log.

**Table 1** Parameter description
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	[2022-02-14T14:23:56+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	HTTP status code returned by the upstream server. When the load balancer attempts to retry a request, there will be multiple HTTP 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	"100.64.0.129:8080" (used by shared load balancers for internal communications)
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	Listener ID. This field can be ignored.	String	3333fd44fe3b42cbaa1dc2c641994d90
pool_name	Backend server group name in the format of pool_backend server group 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	"10.1.1.2:8080"
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	N/A

Log analysis

At 14:23:56 GMT+08:00 on Feb 14, 2022, the load balancer receives an HTTP/1.1 POST request from a client whose IP address and port number are 192.168.1.1 and 888, then routes the request to a backend server whose IP address and port number are 100.64.0.129 and 8080, and finally returns 200 OK to the client after receiving the status code from the backend server.

Analysis results:

The backend server responds to the request normally.

Configuring Log Transfer

If you want to analyze access logs later, transfer the logs to OBS or Data Ingestion Service (DIS) for storage.

Log in to the management console.
In the upper left corner of the page, click and select the desired region and project.
Click in the upper left corner and Management & Governance > Log Tank Service.
In the navigation pane on the left, choose Log Transfer.
On the Log Transfer page, click Configure Log Transfer in the upper right corner.
Figure 5 Configuring log transfer
Configure the parameters. For details, see the Log Tank Service User Guide.