Varnish

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Varnish Cache is a web application accelerator also known as a caching HTTP reverse proxy. You install it in front of any server that speaks HTTP and configure it to cache the contents.

Multiple backends

By default, varnish comes configured in /etc/varnish/default.vcl to use localhost:8080 as the only backend, default.vcl is called by the default systemd varnish.service file :

 /usr/lib/systemd/system/varnish.service 
[Unit]
Description=Web Application Accelerator
After=network.target

[Service]
ExecStart=/usr/bin/varnishd -a 0.0.0.0:80 -f /etc/varnish/default.vcl -T localhost:6082 -s malloc,64M -u nobody -g nobody -F
ExecReload=/usr/bin/varnish-vcl-reload

[Install]
WantedBy=multi-user.target

systemctl enable merely makes a symlink to the default

$ systemctl enable varnish
ln -s '/usr/lib/systemd/system/varnish.service' '/etc/systemd/system/multi-user.target.wants/varnish.service'

instead copy it and edit to increase malloc default.vcl etc:

$ cp '/usr/lib/systemd/system/varnish.service' '/etc/systemd/system/varnish.service'

then enable varnish and it will use your customized .service file instead:

$ systemctl enable varnish
ln -s '/etc/systemd/system/varnish.service' '/etc/systemd/system/multi-user.target.wants/varnish.service'

Also, if you change the config file /etc/varnish/default.vcl you'll need to reload varnish:

$ systemctl reload varnish.service

or restart

$ systemctl restart varnish.service

Manual VCL load

If the previous VCL configuration reload failed, try loading the VCL file manually:

  1. Connect to the varnish console:
    $ varnishadm -T localhost:6082
  2. Load the default VCL. Make sure it has at least one backend:
    varnish> vcl.load default /etc/varnish/default.vcl
  3. Make it active:
    varnish> vcl.use default
  4. Start the child proccess (optional):
    varnish> start