AWS Transfer Family now delivers logs in a structured JSON format across all resources – including servers, connectors, and workflows – and all protocols – including SFTP, FTPS, FTP, and AS2. The new format allows you to easily parse and query your logs using CloudWatch Log Insights, which automatically discovers JSON formatted fields. You’ll also benefit from improved monitoring with support for CloudWatch Contributor Insights, which requires a structured log format to track top users, total number of unique users, and their ongoing usage.
Source:: Amazon AWS