CLI - bossing Varnish around¶
varnishd is started, you can control it using the
program and the command line interface:
If you want to run
varnishadm from a remote system, we recommend
ssh into the system where
varnishd runs. (But see also:
Local and remote CLI connections)
You can SSH into the
varnishd computer and run
ssh $hostname varnishadm help
If you give no command arguments,
varnishadm runs in interactive mode
with command-completion, command-history and other comforts:
critter phk> ./varnishadm 200 ----------------------------- Varnish Cache CLI 1.0 ----------------------------- FreeBSD,13.0-CURRENT,amd64,-jnone,-sdefault,-sdefault,-hcritbit varnish-trunk revision 2bd5d2adfc407216ebaa653fae882d3c8d47f5e1 Type 'help' for command list. Type 'quit' to close CLI session. Type 'start' to launch worker process. varnish>
The CLI always returns a three digit status code to tell how things went.
200 and 201 means OK, anything else means that some kind of trouble prevented the execution of the command.
(If you get 201, it means that the output was truncated, See the cli_limit parameter.)
When commands are given as arguments to
varnishadm, a status
different than 200 or 201 will cause it to exit with status 1
and print the status code on standard error.
What can you do with the CLI¶
From the CLI you can:
load/use/discard VCL programs
ban (invalidate) cache content
start/stop worker process
We will discuss each of these briefly below.
Load, use and discard VCL programs¶
All caching and policy decisions are made by VCL programs.
You can have multiple VCL programs loaded, but one of them is designated the “active” VCL program, and this is where all new requests start out.
To load new VCL program:
varnish> vcl.load some_name some_filename
Loading will read the VCL program from the file, and compile it. If the compilation fails, you will get an error messages:
.../mask is not numeric. ('input' Line 4 Pos 17) "192.168.2.0/24x", ----------------#################- Running VCC-compiler failed, exit 1 VCL compilation failed
If compilation succeeds, the VCL program is loaded, and you can now make it the active VCL, whenever you feel like it:
varnish> vcl.use some_name
If you find out that was a really bad idea, you can switch back to the previous VCL program again:
varnish> vcl.use old_name
The switch is instantaneous, all new requests will start using the VCL you activated right away. The requests currently being processed complete using whatever VCL they started with.
We highly recommend you design an emergency-VCL, and always keep it loaded, so it can be activated with
Ban cache content¶
Varnish offers “purges” to remove things from cache, but that requires you to know exactly what they are.
Sometimes it is useful to be able to throw things out of cache without having an exact list of what to throw out.
Imagine for instance that the company logo changed and now you need Varnish to stop serving the old logo out of the cache:
varnish> ban req.url ~ "logo.*[.]png"
should do that, and yes, that is a regular expression.
We call this “banning” because the objects are still in the cache, but they are now banned from delivery, while all the rest of the cache is unaffected.
Even when you want to throw out all the cached content, banning is both faster and less disruptive that a restart:
varnish> ban obj.http.date ~ .*
Parameters can be set on the command line with the ‘-p’ argument, but almost all parameters can be examined and changed on the fly from the CLI:
varnish> param.show prefer_ipv6 200 prefer_ipv6 off [bool] Default is off Prefer IPv6 address when connecting to backends which have both IPv4 and IPv6 addresses. varnish> param.set prefer_ipv6 true 200
In general it is not a good idea to modify parameters unless you have a good reason, such as performance tuning or security configuration.
Most parameters will take effect instantly, or with a short delay, but a few of them requires you to restart the child process before they take effect. This is always mentioned in the description of the parameter.
Starting and stopping the worker process¶
In general you should just leave the worker process running, but if you need to stop and/or start it, the obvious commands work:
If you start
varnishd with the ‘-d’ (debugging) argument, you will
always need to start the child process explicitly.
Should the child process die, the master process will automatically restart it, but you can disable that with the auto_restart parameter.