An access log is generated by the web server to log the details about the request that it has processed. It logs status code, response time, URL, protocol, size, client IP address, etc., about the request. Load Balancers will have similar log files created to log the request details. While doing any performance analysis, these logs play an important role. It is being neglected most of the time due to lack of awareness and the usage of APM tools abstracts it from the users by allowing them to focus visually on coarse-grained data instead of fine-grained data. Most people are aware of the application server log but many of them are not aware of the web server/load balancer access log. Most of the time, this log will not be striking in the mind of a person who investigates the problem.
Access logs are available for the below servers while the format for each of them varies: