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Changing where log files are written
Last updated July 14, 2017
For supported logging endpoints that write files to remote services, Fastly uses a combination of factors to ensure log files aren't overwritten, including:
- Using the file creation timestamp.
- Generating a unique ID.
- If a file with the same timestamp and UID combination exists, incrementing a counter and adding that to the end of the filename.
To change where log files are written, you can modify the
timestamp_format variables. The logging system combines the
uid variables to create the file name:
This guide explains how to use the
timestamp_format variables to control where log files are written.
Supported logging endpoints
The following logging endpoints currently support the
You may want to consider changing the timestamp format to remove characters from the log filenames. For example, if you're working with Elastic MapReduce, you might need to remove the colons in the filename.
The variables are expanded when the file is created. For example,
%Y will be replaced by the current year and
%m by the current month number:
<year>-<2 digit month number>-<2 digit day number>T<hour>:<minute>:<second>
The timestamp for a file created at midnight on January 1st, 1970 would be
path variable acts differently depending on whether or not it ends in a trailing
If the variable does end in a trailing
/, then it's treated as a directory. For example, if the variable is set to
my_logs/, the files are written in the directory
my_logs. If the variable is set to
my_logs without the trailing
/, the files are written in the top-level directory and are prefixed with
The two approaches can also be combined. For example, if the variable is set to
my_logs/foo, the files are written in the
my_logs directory and are prefixed with
Logs can also be nested. For example, if the variable is set to
my_logs/sub_logs/, the files are written in the
sub_logs directory in the
TIP: The path can also be a
strftime compatible string. For example, if the variable is set to
%Y/%m/%d, the files are written to a directory based on the year, month, and date.
Directories are created automatically when possible.
Fastly's logging system automatically adds suffixes to files as appropriate.
|.log||Plain log file|
|.log.gz||Gzipped log file|
|.log.gpg||PGP encrypted log file|
|.log.gz.gpg||PGP encrypted, Gzipped log file|