| Author: | Per Buer |
|---|---|
| Date: | 2011-03-23 |
| Version: | 0.1 |
| Manual section: | 7 |
Varnish as a command line interface (CLI) which can control and change most of the operational parameters and the configuration of Varnish, without interrupting the running service.
The CLI can be used for the following tasks:
If you invoke varnishd(1) with -T, -M or -d the CLI will be available. In debug mode (-d) the CLI will be in the foreground, with -T you can connect to it with varnishadm or telnet and with -M varnishd will connect back to a listening service pushing the CLI to that service. Please see varnishd(1) for details.
Commands are usually terminated with a newline. Long command can be entered using sh style here documents. The format of here-documents is:
<< word
here document
word
word can be any continuous string choosen to make sure it doesn't appear naturally in the following here document.
When using the here document style of input there are no restrictions on lenght. When using newline-terminated commands maximum lenght is limited by the varnishd parameter cli_buffer.
When commands are newline terminated they get tokenized before parsing so if you have significant spaces enclose your strings in double quotes. Within the quotes you can escape characters with \. The n, r and t get translated to newlines, carrage returns and tabs. Double quotes themselves can be escaped with a backslash.
To enter characters in octals use the \nnn syntax. Hexadecimals can be entered with the \xnn syntax.
All requests for objects from the cache are matched against items on the ban list. If an object in the cache is older than a matching ban list item, it is considered "banned", and will be fetched from the backend instead.
When a ban expression is older than all the objects in the cache, it is removed from the list.
ban.list displays the ban list. The output looks something like this (broken into two lines):
0x7fea4fcb0580 1303835108.618863 131G req.http.host ~ www.myhost.com && req.url ~ /some/url
The first field is the address of the ban.
The second is the time of entry into the list, given as a high precision timestamp.
The third field describes many objects point to this ban. When an object is compared to a ban the object is marked with a reference to the newest ban it was tested against. This isn't really useful unless you're debugging.
A "G" marks that the ban is "Gone". Meaning it has been marked as a duplicate or it is no longer valid. It stays in the list for effiency reasons.
Then follows the actual ban it self.
Display a list if run-time parameters and their values.
If the -l option is specified, the list includes a brief explanation of each parameter.
If a param is specified, display only the value and explanation for this parameter.
A ban expression consists of one or more conditions. A condition consists of a field, an operator, and an argument. Conditions can be ANDed together with "&&".
A field can be any of the variables from VCL, for instance req.url, req.http.host or obj.http.set-cookie.
Operators are "==" for direct comparision, "~" for a regular expression match, and ">" or "<" for size comparisons. Prepending an operator with "!" negates the expression.
The argument could be a quoted string, a regexp, or an integer. Integers can have "KB", "MB", "GB" or "TB" appended for size related fields.
If you are going to write a script that talks CLI to varnishd, the include/cli.h contains the relevant magic numbers.
One particular magic number to know, is that the line with the status code and length field always is exactly 13 characters long, including the NL character.
For your reference the sourcefile lib/libvarnish/cli_common.h contains the functions varnish code uses to read and write CLI response.
If the -S secret-file is given as argument to varnishd, all network CLI connections must authenticate, by proving they know the contents of that file.
The file is read at the time the auth command is issued and the contents is not cached in varnishd, so it is possible to update the file on the fly.
Use the unix file permissions to control access to the file.
An authenticated session looks like this:
critter phk> telnet localhost 1234
Trying ::1...
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
107 59
ixslvvxrgkjptxmcgnnsdxsvdmvfympg
Authentication required.
auth 455ce847f0073c7ab3b1465f74507b75d3dc064c1e7de3b71e00de9092fdc89a
200 193
-----------------------------
Varnish HTTP accelerator CLI.
-----------------------------
Type 'help' for command list.
Type 'quit' to close CLI session.
Type 'start' to launch worker process.
The CLI status of 107 indicates that authentication is necessary. The first 32 characters of the reponse text is the challenge "ixsl...mpg". The challenge is randomly generated for each CLI connection, and changes each time a 107 is emitted.
The most recently emitted challenge must be used for calculating the authenticator "455c...c89a".
The authenticator is calculated by applying the SHA256 function to the following byte sequence:
and dumping the resulting digest in lower-case hex.
In the above example, the secret file contained foon and thus:
critter phk> cat > _
ixslvvxrgkjptxmcgnnsdxsvdmvfympg
foo
ixslvvxrgkjptxmcgnnsdxsvdmvfympg
^D
critter phk> hexdump -C _
00000000 69 78 73 6c 76 76 78 72 67 6b 6a 70 74 78 6d 63 |ixslvvxrgkjptxmc|
00000010 67 6e 6e 73 64 78 73 76 64 6d 76 66 79 6d 70 67 |gnnsdxsvdmvfympg|
00000020 0a 66 6f 6f 0a 69 78 73 6c 76 76 78 72 67 6b 6a |.foo.ixslvvxrgkj|
00000030 70 74 78 6d 63 67 6e 6e 73 64 78 73 76 64 6d 76 |ptxmcgnnsdxsvdmv|
00000040 66 79 6d 70 67 0a |fympg.|
00000046
critter phk> sha256 _
SHA256 (_) = 455ce847f0073c7ab3b1465f74507b75d3dc064c1e7de3b71e00de9092fdc89a
critter phk> openssl dgst -sha256 < _
455ce847f0073c7ab3b1465f74507b75d3dc064c1e7de3b71e00de9092fdc89a
The sourcefile lib/libvarnish/cli_auth.c contains a useful function which calculates the response, given an open filedescriptor to the secret file, and the challenge string.
Simple example: All requests where req.url exactly matches the string /news are banned from the cache:
req.url == "/news"
Example: Ban all documents where the name does not end with ".ogg", and where the size of the object is greater than 10 megabytes:
req.url !~ "\.ogg$" && obj.size > 10MB
Example: Ban all documents where the serving host is "example.com" or "www.example.com", and where the Set-Cookie header received from the backend contains "USERID=1663":
req.http.host ~ "^(?i)(www\.)example.com$" && obj.http.set-cookie ~ "USERID=1663"
The varnish manual page was written by Per Buer in 2011. Some of the text was taken from the Varnish Cache wiki, the varnishd(7) man page or the varnish source code.
This document is licensed under the same licence as Varnish itself. See LICENCE for details.