How to configure vcl_log

In order to configure vcl_log, you’ll use custom VCL.

For example, the variable resp.bytes_written is available in vcl_log, not vcl_deliver.

So here’s how you would configure that (this assumes that you already have logging set up via the UI):

Copy your current log format from vcl_deliver and add that to your custom VCL under a new subroutine, vcl_log. Include any additional variables you would like to the format string (e.g., in this scenario, resp.bytes_written).
Add a condition to your log in the UI that will always be false (e.g. if (!req.url) ), thus prioritizing your logging configuration set in vcl_log over vcl_deliver.

Your file should look something similar to:

sub vcl_log{

   log {"syslog <service_id> <logging endpoint name> :: "} req.http.Fastly-Client-IP {" "} {""-""} {" "} {""-""} {" "} now {" "} req.request " " req.url {" "}  resp.bytes_written {" "};

}

Note: In custom VCL be sure to include the #FASTLY deliver macro in your vcl_deliver handler.

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