.. _users_intro:
The Big Varnish Picture
=======================
In this section we will cover answers to the questions:
- What is in this package called "Varnish"?
- what are all the different bits and pieces named?
- Will you need a hex-wrench for assembly?
The two main parts of Varnish are the two processes in the `varnishd`
program. The first process is called "the manager", and its job is to
talk to you, the administrator, and make the things you ask for
happen.
The second process is called "the worker" or just "the child" and
this is the process which does all the actual work with your HTTP
traffic.
When you start `varnishd`, you start the manager process, and once it is
done handling all the command line flags, it will start the child
process for you. Should the child process die, the manager will start
it again for you, automatically and right away.
The main reason for this division of labor is security: The manager
process will typically run with "root" permissions, in order to
open TCP socket port 80, but it starts the child process with minimal
permissions, as a defensive measure.
The manager process is interactive, it offers a CLI -- Command Line
Interface, which can be used manually, from scripts or programs. The
CLI offers almost full control of what Varnish actually does to your
HTTP traffic, and we have gone to great lengths to ensure that you
should not need to restart the Varnish processes, unless you need to
change something very fundamental.
The CLI can be safely accessed remotely, using a simple and flexible
PSK -- Pre Shared Key, access control scheme, so it is easy to
integrate Varnish into your operations and management infrastructure
or tie it to your CMS.
All this is covered in :ref:`users_running`.
Things like, how the child process should deal with the HTTP requests, what to
cache, which headers to remove etc, is all specified using a small
programming language called VCL -- Varnish Configuration Language.
The manager process will compile the VCL program and check it for
errors,
.. XXX:What does manager do after compile and error-check? Maybe a short description of further handling when no errors as well as when errors? benc
but it is the child process which runs the VCL program, for
each and every HTTP request which comes in.
Because the VCL is compiled to C code, and the C code is compiled
to machine instructions, even very complex VCL programs execute in
a few microseconds, without impacting performance at all.
And don't fret if you are not really a programmer, VCL is very
simple to do simple things with::
sub vcl_recv {
# Remove the cookie header to enable caching
unset req.http.cookie;
}
The CLI interface allows you to compile and load new VCL programs
at any time, and you can switch between the loaded VCL programs
instantly, without restarting the child process and without missing
a single HTTP request.
VCL code can be extended using external modules, called VMODs or
even by inline C-code if you are brave, so in terms of what Varnish
can do for your HTTP traffic, there really is no limit.
:ref:`users_vcl` describes VCL and what it can do in great detail.
Varnish uses a segment of shared memory to report and log its activities and
status. For each HTTP request, a number of very detailed records will
be appended to the log memory segment. Other processes
can subscribe to log-records, filter them, and format them, for
instance as Apache/NCSA style log records.
Another segment in shared memory is used for statistics counters,
this allows real-time, down to microsecond resolution monitoring
of cache hit-rate, resource usage and specific performance indicating
metrics.
Varnish comes with a number of tools which reports from shared
memory, `varnishlog`, `varnishstats`, `varnishncsa` etc, and with an API
library so you can write your own tools, should you need that.
:ref:`users_report` explains how all that work.
Presumably the reason for your interest in Varnish, is that you
want your website to work better. There are many aspects of
performance tuning a website, from relatively simple policy decisions
about what to cache, to designing a geographically diverse multilevel
CDNs using ESI and automatic failover.
.. XXX:CDNs or CDN? benc
:ref:`users_performance` will take you through the possibilities
and facilities Varnish offers.
Finally, Murphys Law must be referenced here: Things will go wrong, and
more likely than not, they will do so at zero-zero-dark O'clock. Most
likely during a hurricane, when your phone battery is flat and your
wife had prepared a intimate evening to celebrate your anniversary.
Yes, we've all been there, haven't we?
When things go wrong :ref:`users_trouble` will hopefully be of some help.
Henceforth, whatever our philosopher says about Matter will apply to extension and to extension alone. It cannot be apprehended by sight, nor by hearing, nor by smell, nor by taste, for it is neither colour, nor sound, nor odour, nor juice. Neither can it be touched, for it is not a body, but it becomes corporeal on being blended with sensible qualities. And, in a later essay, he describes it as receiving all things and letting them depart again without retaining the slightest trace of their presence.483 Why then, it may be asked, if Plotinus meant extension, could he not say so at once, and save us all this trouble in hunting out his meaning? There were very good reasons why he should not. In the first place, he wished to express himself, so far as possible, in Aristotelian phraseology, and this was incompatible with the reduction of Matter to extension. In the next place, the idea of an infinite void had been already appropriated by the Epicureans, to whose system he was bitterly opposed. And, finally, the extension of ordinary327 experience had not the absolute generality which was needed in order to bring Matter into relation with that ultimate abstraction whence, like everything else, it has now to be derived. That the millionaire was genuine, ¡°in person and not a caricature,¡± as Dick put it, was evident. Both the nurse, his relative, and his wife, were chatting with him as Jeff delivered the heavy packed ball made up of the gum. 233 "I guess not," said Landor, tolerantly, as he turned[Pg 106] his horse over to his orderly; "but, anyway," he added to Ellton, "we had a picnic¡ªof a sort." Si, unable to think of anything better, went with him. The train had stopped on a switch, and seemed likely to rust fast to the rails, from the way other trains were going by in both directions. The bridge gang, under charge of a burly, red-faced young Englishman, was in the rear car, with their tools, equipments, bedding and cooking utensils. THE DEACON HAS SOME EXPERIENCES WITH THE QUADRUPED. "You are not within a mile of the truth. I know it. Look here: I believe that is Gen. Rosecrans's own cow. She's gone, and I got an order to look around for her. I've never seen her, but from the description given me I believe that's she. Who brought her here?" "Deacon, these brothers and sisters who have come here with me to-night are, like myself, deeply interested in the moral condition of the army, where we all have sons or kinsmen. Now, can't you sit right there and tell us of your observations and experiences, as a Christian man and father, from day to day, of every day that you were down there? Tell us everything, just as it happened each day, that we may be able to judge for ourselves." HAS AN ENCOUNTER WITH THE PROVOST-MARSHAL. "Wonder which one o' them is the 200th Injianny's?" said Si to Shorty. "And your mother, and Harry?" The daughter must be the girl who was talking to him now. She sat on a little stool by the fire, and had brought out some sewing. "Over at Grandturzel¡ªcan't see wot's burning from here. Git buckets and come!" These things, however, gave little concern to the worthy who commanded the Kentish division. Tyler, though an excellent blacksmith, possessed few of the qualities requisite for forming a good general. Provided there was no very sensible diminution in the number of his followers, he cared not a straw for the score or two who, after quarrelling, or perhaps fighting, withdrew in such disgust that they vowed rather to pay the full tax for ever than submit to the insolence of the rebels. One man could fight as well as another, reasoned he; and, provided he was obeyed, what mattered it by whom. Dick went and Tom came¡ªit was sure to be all one in the end. But this burst of indignation soon passed away, and upon the suggestion of the prudent Sir Robert Hailes, he sent an evasive answer, with a command that the Commons should attend him at Windsor on the Sunday following. That it was a stratagem to gain entrance to the Tower, was the opinion of several, but, after much discussion, it was decided that the man should be admitted, and that the monk should be exhibited merely to intimidate the rebels, until the result of this promised communication should be known. HoMEŮͬÐÔÁµcbcb
ENTER NUMBET 0017
memu6.com.cn
www.jkwc.net.cn
loonco.com.cn
www.ssuper.com.cn
dimin1.com.cn
delei6.net.cn
kezhi4.com.cn
lubao2.net.cn
www.chaci3.net.cn
arts08.com.cn