Retrieve application log files

Log files are a great resource for a Web developer, but only if you know how to find and use the logged information. Here, you look at the methods you can use to retrieve logged information for offline analysis.

Log file storage locations

The Azure infrastructure used to run Azure Web Apps in Windows isn’t the same as for Linux apps, and log files aren’t stored in the same locations.

Windows app log files

For Windows apps, file system log files are stored in a virtual drive that is associated with your Web App. This drive is addressable as D:\Home, and includes a LogFiles folder; within this folder are one or more subfolders:

• Application – Contains application-generated messages, if File System application logging is enabled.
• DetailedErrors – Contains detailed Web server error logs, if Detailed error messages are enabled.
• http – Contains IIS-level logs, if Web server logging is enabled.
• W3SVC<number> – Contains details of all failed http requests, if Failed request tracing is enabled.

Where storage to a Blob container is enabled, logs are stored in year, month, date, and hour folders, for example:Copy

2019
  01
   10
    08 - log entries for the period 08:00:00 to 08:59:59 on January 10th 2019
    09 - log entries for the period 09:00:00 to 09:59:59 on January 10th 2019

Within the hour folder, there are one or more CSV files containing messages saved within that 60-minute period.

Linux app log files

For Linux Web Apps, the Azure tools currently support fewer logging options than for Windows apps. Redirections to STDERR and STDOUT are managed through the underlying Docker container that runs the app, and these messages are stored in Docker log files. To see messages logged by underlying processes, such as Apache, you need to open an SSH connection to the Docker container.

Methods for retrieving log files

How you retrieve log files depends on the type of log file, and on your preferred environment. For file system logs, you can use the Azure CLI or the Kudu console. Kudu is the engine behind many features in Azure App Service related to source control based deployment.

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