SearchBy default, installation of varnishd will not write request logs to disk. Varnish has an in-memory log with tools to tap into and write to disk.
You’ll need:
-A Linux-based server with a privileged account or with sudo capabilities -Varnish Enterprise or Varnish Cache installed (You can use your distribution-supplied packages or head over to the official site for installation instructions
This guide was written and tested with Varnish version 4.1.x, but will also work with Varnish 5.x.
Enabling varnishncsa to run as a service is based on your Linux distribution, type, and version:
| Distribution | Version | Type |
|---|---|---|
| CentOS | 6 | Non-systemd |
| Red Hat EL | 6 | Non-systemd |
| CentOS | 7 | Systemd |
| Red Hat EL | 7 | Systemd |
| Debian | 8 (Jessie) | Systemd |
| Debian | 9 (Stretch) | Systemd |
| Ubuntu | 14.04 (Trusty) | Non-systemd |
| Ubuntu | 16.04 (Xenial) | Systemd |
On CentOS6/RHEL6, use chkconfig to enable the service on boot:
chkconfig --level 345 varnishncsa on
On Debian/Ubuntu, edit /etc/default/varnishncsa and uncomment the line below by removing the # at the start of the line:
VARNISHNCSA_ENABLED=1
When you check the status, the service should not be running yet:
service varnishncsa status
* varnishncsa is not running
You can add custom options to the startup by adding a DAEMON_OPTS line to:
/etc/sysconfig/varnishncsa (CentOS6/RHEL6)
/etc/default/varnishncsa (Debian/Ubuntu)
Example of adding -c to the defaults:
DAEMON_OPTS="-a -w ${LOGFILE} -D -P ${PIDFILE} -c"
*To escape the output log format string, see the note in Customize options in the systemd-based distro section.
Output might differ based on your distribution:
service varnishncsa start
* Starting Varnish Enterprise NCSA logging daemon varnishncsa
Confirm it is running:
ps aux | grep varnishncsa
varnish+ 1844 0.3 0.0 99208 176 ? Ss 09:33 0:00 /usr/bin/varnishncsa -a -w /var/log/varnish/varnishncsa.log -D -P /var/run/varnishncsa/varnishncsa.pid
Enable systemd varnishncsa.service so it will autostart on boot:
systemctl enable varnishncsa
The service should not be started:
systemctl status varnishncsa
● varnishncsa.service - Varnish Enterprise HTTP accelerator log daemon
Loaded: loaded (/lib/systemd/system/varnishncsa.service; enabled; vendor preset: enabled)
Active: inactive (dead)
You can edit the options passed to varnishncsa by editing ExecStart in the varnishncsa.service file.
In systemd, use the edit command:
systemctl edit varnishncsa
This will open a blank file allowing you to enter overrides for the service.
Example of adding -c to the defaults:
[Service]
ExecStart=
ExecStart=/usr/bin/varnishncsa -a -w /var/log/varnish/varnishncsa.log -D -c
To use a customized output log format string, just read the string from a file via the -f <formatfile> option:
[Service]
ExecStart=
ExecStart=/usr/bin/varnishncsa -a -w /var/log/varnish/varnishncsa.log -D -c -f /my_custom_format
Example of formatfile contents:
$ cat /my_custom_format
%{Host}i %h %l %u %t "%r" %s %b "%{Referer}i" "%{User-agent}i"
$
To use a customized output log format string in the systemd unit file, you need to escape percent signs, %, and double quotes, ".
Example on the command line requires no escaping:
$ /usr/bin/varnishncsa -F '%{Host}i %h %l %u %t "%r" %s %b "%{Referer}i" "%{User-agent}i"'
From the systemd unit file, the escaped string will look like this:
[Service]
ExecStart=
ExecStart=/usr/bin/varnishncsa -a -w /var/log/varnish/varnishncsa.log -D -c -F "%%{Host}i %%h %%l %%u %%t \\\"%%r\\\" %%s %%b \\\"%%{Referer}i\\\" \\\"%%{User-agent}i\\\" "
systemctl start varnishncsa
Confirm it is running with the status command. This output will differ slightly on different distros:
systemctl status varnishncsa
● varnishncsa.service - Varnish Enterprise HTTP accelerator log daemon
Loaded: loaded (/usr/lib/systemd/system/varnishncsa.service; enabled; vendor preset: disabled)
Active: active (running) since Fri 2017-12-15 10:18:22 UTC; 2s ago
Process: 8476 ExecStart=/usr/bin/varnishncsa -a -w /var/log/varnish/varnishncsa.log -D -P /var/run/varnishncsa/varnishncsa.pid (code=exited, status=0/SUCCESS)
Main PID: 8477 (varnishncsa)
CGroup: /system.slice/varnishncsa.service
└─8477 /usr/bin/varnishncsa -a -w /var/log/varnish/varnishncsa.log -D -P /var/run/varnishncsa/varnishncsa.pid
Dec 15 10:18:22 centos-7-amd64.local systemd[1]: Starting Varnish Enterprise HTTP accelerator log daemon...
Dec 15 10:18:22 centos-7-amd64.local systemd[1]: Started Varnish Enterprise HTTP accelerator log daemon.
To customize logging, either the format of the loglines or only log certain lines, return to Step 3 from the above instructions and edit the startup options for varnishncsa.
For more information on the available options, see the varnishncsa documentation.
Examples that might prove useful:
To only log for response or backend response status codes above 399, add the below query:
-q "RespStatus >= 400 or BerespStatus >= 400"
To log all requests that took more than two seconds to be delivered or with a non-200 response status, add the below query:
-q "Timestamp:Resp[3] > 2.0 or RespStatus != 200"
To only log requests for a certain domain (e.g., example.com), add the following:
-q "ReqHeader ~ '^Host: .*\.example.com'"
After customizing the logs, restart varnishncsa. These steps are for restarting varnishncsa on systemd-based distributions. For an in-depth systemd tutorial, see Configuring Systemd Services.
Stop the varnishncsa daemon and kill any varnishncsa processes:
$ sudo systemctl stop varnishncsa
$ ps auxww | grep -e PID -e varnishncsa
$ kill pid_of_running_varnishncsa_process
Check for unused override files and comment varnishncsa, if necessary:
$ systemctl cat varnishncsa
$ sudo vi override_file_from_previous_command
A customized log format can be present in /etc/rc.local, /etc/default/varnishncsa (Non-systemd CentOS6/RHEL6), and /etc/sysconfig/varnishncsa (Non-systemd Debian/Ubuntu).
In Non-systemd based distributions, these files are used. In systemd-based distributions, these files are not used and any varnishncsa override present in them should be commented to avoid confusion.
Confirm the updates made to varnishncsa are present, reload systemctl, and start varnishncsa:
$ sudo systemctl cat varnishncsa
$ sudo systemctl daemon-reload
$ sudo systemctl start varnishncsa
Tail the varnishncsa log to view the updated output. This is the argument to the -w option, which is typically /var/log/varnish/varnishncsa.log:
$ tail -f /var/log/varnish/varnishncsa.log
On a high-volume system, logging to disk will quickly eat up space, so it is imperative to set up proper log rotation.
Most Varnish packages that supply a varnishncsa service will also contain a base config for logrotate, but configuring this depends heavily on your setup and traffic. This is out of the scope of this tutorial. See man logrotate or this DigitalOcean logrotate tutorial for more information, and see /etc/logrotate.d/varnish for the default.
After completing this guide, you should now receive requests logged into /var/log/varnish/varnishncsa.log on your host.