Web Content Caching Explained

The minefield that is web content caching can be confusing and complicated!

It’s one of those features that really sits between the network and the application. In many businesses this grey area has no real ownership and as such, mistakes are often made.

I want to take a little time to explore and hopefully simplify this complex area.

So firstly one must address the question of what is a content cache and why bother using it?

A content cache is a piece of software or an appliance designed to sit in front of the application server. Its job is to intercept certain requests and respond on behalf of the application thus reducing the number of hits sent to the backend severs.

Typically the requests that are intercepted have already been seen before, so the cache will store responses to these requests and if it intercepts a similar request it can respond in the same way.

A simple example would be an image cache. The client (ie browser) would make a response to the web server for an image. The first time this image is requested the cache will have to get it from the web server however for subsequent requests it will simply serve it directly.

The idea is that the web server will have a lot less work to do as the cache can serve a lot of the content. The implications of this really depend on the exact setup, application and content however they typically fit into the following:

1. Reduce load on the web/application servers – Save on application server hardware and licensing costs.

2. Reduce load on middleware and Backed DB systems.

3. Serve the content faster – Caches can be very fast!

4. Cache the content closer to your users. This is an interesting one. The cache does not always have to be at the same location as the rest of the system. You could use a good cache to build your own simple content distribution system to ensure your users get the content from a source as close to them as possible. Who said that a CDN (Content Distribution Network) has to cost the earth!

OK so you have decided that you may want to use a cache, so what next? The biggest problem with content caching is simply deciding what and for how long you want to cache content for. It sounds simple but failure to do this in the past has given many a network manager / application owner a genuine fear of caching. You don’t want one user getting the account balance of the previous user!

However to really make the most of the capabilities that a modern content cache can offer we must understand the full picture. The application behaviour, the cache setup and the browser behaviour.

Let us take a quick look at typically what happens when an image is requested from a web server by a browser.

1. The user requests an image to look at.

2. The Cache will notice that it has not seen this request before and therefore will request it from the web server.

3. The web server will get the image and send it back to the cache.

Important. The web server will decide if this image can be cached or not. It will instruct the upstream devices such as the cache and ultimately the client if it should be cached it or not. It does this by using specific HTTP header. (I won’t geek out on this, in this article as it can get overly complex.)

4. Now it gets interesting because the cache will need to decide on which way to go. Does it obey the rules from the web server or does it override it with its own rules? We will discuss this later on.

5. So the image is now sent back to the client and just to complicate things the client will also cache the content and also look out for the cache control header.

So we can see that not only do we have to decide on the application caching rules but also how we want the cache to behave upstream. If we do this right we can even reduce the number of hits reaching the cache and thus network in the first place.

So now we have a rough idea of what is going on, so how do we implement a cache?

A general method is described in “light” detail below.

1. Decide what you want to cache and for how long – So I want to cache all images for 24hours or all *.asp for 2seconds etc. These can get complicated.

2. Be certain you are happy with these rules.

3. Now check again.

4. Configure the cache to remove all cache control headers from the response from the web server. In other words ignore any caching control setup on the webserver – We assume we know how to create more accurate set of rules.

5. Configure the cache with these new rules and also expiry dates/ durations.

6. Configure the cache to add some new cache controls for the Client. Client side cache control is tough as browsers respect these rules with varying degrees of success. This is not really in the scope of this paper but I may revisit it.

7. Document – These rules can be complex and can involve speaking to people in different parts of the business to understand the application, therefore it’s worth documenting this info whilst it is fresh.

8. Test and test again – The more testing the better. Remember part of testing is to manually empty the content cache’s cache but also the client’s too.

That’s it for now folks.

I am writing a follow up on this talking in a little more detail about typical cache settings and also helping to answer questions such as, ‘will a cache be of any help for my application and if so what type of cache should I be looking at?’

Speeding PHP Using APC PHP Cache

If you look at a PHP source file you will notice one thing. It’s a source file. Not particularly surprising, but think about when you deploy a PHP application, what do you deploy? PHP source files. Now for many other languages; Java, C, etc when you deploy an application you deploy the compiled file. So, the question that you want to ask yourself is this, how much time does a PHP application spend compiling source files vs running the code? I’ll answer that for you, a lot.

There are advantages to being able to deploy source files though. It makes it easy to do on the fly modifications or bug fixes to a program, much like we used to do in the early BASIC languages. Just change the file and the next time it’s accessed your change is reflected. So, how do we keep the dynamic nature of PHP, but not recompile our files every time they are accessed?

A PHP cache. It’s surprising to me that this concept isn’t built into the base PHP engine, but perhaps that’s because some company’s can sell this add on to speed up PHP. Luckily for us, some companies/open source projects provide this plug in to PHP at no charge. These plug ins are generally known as PHP accelerators, some of them do some optimization and then caching and some only do caching. I’m not going to pass judgement on which one is the best, any of them are better than nothing, but I decided to use APC, the Alternative PHP Cache. I chose this one because it is still in active development and is open source and free.

Alternative php cache can be found at php.net, just look down the left column for APC. It comes in source form, so you will need to compile it before installing it, don’t worry about that part. If you’re using Red Hat 4 or CentOS4 I’ll tell you exactly how to do it. If you’re using something else, you’ll need the same tools, but getting the tools might be a bit different.

1. The Tools

Do you know how many web sites, forums and blogs I went to with my error messages before I found the answers as to what I was missing when I was trying to install APC – Alternative PHP Cache? Two days worth, but I finally found the correct combination and it’s really quite obvious as is everything once you know the answer. There are three sets of dev tools that you will need.

1a. You’ll need a package called “Development Tools” this will include all the important dev tools like the GCC compiler, etc.

1b. You’ll need a package called php-devel which as you might guess are development tools for PHP

1c. You’ll need a package called httpd-devel which of course are dev tools for Apache web server.

On Red Hat or CentOS getting these should be as easy as the following 3 commands:

yum groupinstall “Development Tools”

yum install php-devel

yum install httpd-devel

You’ll do these three one at a time and follow any instructions (usually just saying yes).

Now it’s time to follow the instructions contained in the APC package. Since these may change over time I’m not going to go through them. They are very complete. If you follow the instructions and get an apc.so file out of it, then you’re all set, just modify your php.ini file and you’re good to go.

There are two problems that I encountered that you may encounter too. The first is an error when running phpize. I ignored this error and everything succeeded okay, but not before I spent hours looking for the solution to this error. Here is the error.

configure.in:9: warning: underquoted definition of PHP_WITH_PHP_CONFIG

run info ‘(automake)Extending aclocal’

or see http://sources.redhat.com/automake/automake.html#Extending-aclocal

configure.in:32: warning: underquoted definition of PHP_EXT_BUILDDIR

configure.in:33: warning: underquoted definition of PHP_EXT_DIR

configure.in:34: warning: underquoted definition of PHP_EXT_SRCDIR

configure.in:35: warning: underquoted definition of PHP_ALWAYS_SHARED

acinclude.m4:19: warning: underquoted definition of PHP_PROG_RE2C

People would have had me updating my PHP version from 4.3.9 and everything else under the sun to get rid of this error, but in the end it didn’t matter. My APC compiled and installed nicely and I am good to go.

The other slight problem that I ran into was the location of php-config. The install instructions wanted me to do the following:

./configure –enable-apc-mmap –with-apxs
–with-php-config=/usr/local/php/bin/php-config

However my php-config is in /usr/bin/php-config. Making that change allowed this part to work.

So, have at it, once it’s done you can expect to see huge improvements in your web site response times and reductions on your CPU load. One more quick note, My server hosts about 20 web sites, but only 3 or 4 are really busy. To reduce the memory footprint of caching everything for all 20 sites I used the apc.filters property. Although this property is slightly flawed for non qualified includes, it worked nicely for my Serendipity blogs. Your mileage with this property will vary according to the software you are using and how it does it’s includes.

Foreclosure Cleanup – How to Make Money Today With Your Business

Years ago, I had an office in New York City, right down from Madison Square Garden. My little office was on the fourth floor of a small commercial building. There were several small businesses housed on my floor. My small business neighbor was also my accountant. I’ll never forget the words Tony the Accountant said to me one afternoon when he peeked into my office for a chat. He said, “Always ask yourself, what can I do to make money TODAY?”

Your Primary Task Each Day: I’ve gone back to that statement over and over again throughout the years. Sometimes as business owners we get so mired in running our business, that we forget to consistently make money at what we’re doing. It may sound crazy, but it’s true. The bills have to be paid (money going out); the marketing pieces have to be prepared; the uniforms have to be washed; the truck has to be dumped; the equipment has to be repaired; etc.

But when you first get up in the morning, running around like a mad person to start your daily business tasks, stop and ask yourself that same question that Tony proposed to me: What can you do to bring in a dollar today in your foreclosure cleanup business? Whatever else you may have on your plate should really take a back seat until you have done the primary task that will add money to your bank account that day.

If you don’t succeed, you will have put out a ton of feelers that may turn into cash the next day or later in the week.

What Services Do You Offer in Your Foreclosure Cleanup Business?

Are you offering services that will allow you to bring in cash on a daily basis? Are these services within your immediate control? Or, are you, instead, offering services that make you sound good, official, but that require you to depend on others to perform those tasks? Can you personally winterize, change locks, handle repairs, do the gutter cleaning, handle the painting? Or do you need a crew to assist you in getting those jobs done TODAY?

Take Inventory of Your List of Services: If you are a new foreclosure cleanup business, take inventory of the list of services you have included as part of your foreclosure cleanup business. Do you need to scale back to be in control of making money TODAY?

As your business grows, of course you will add more and more services to your cache of foreclosure cleanup duties, and you will add more workers. But, when you’re just starting out, consider offering only those services that you know you can handle yourself. Why? So you can wake up knowing you can put money in your pocket TODAY, all by your lonesome, if you have to.

Your business won’t seem as big, but you will be making more money. And that’s what business is about: making money, profit, being able to pay yourself a decent salary, consistently.

Take Action Today: For example, using Tony’s question (What can you do to make money today?), you can wake up on a Saturday morning and decide you want to put $300 in your pocket before night fall, all by yourself, in your new real estate and foreclosure cleanup business. Put your lawn mower on the back of your truck (a truck that should hold your company’s magnet signs), and hit every home and business within a ten mile radius, offering a Special Today Only rate for lawn care.

Worst Case Scenario: Those eventual customers that may say no today will now know your business name and have your company flier, which should list all of your real estate and foreclosure cleanup services.

Remember, you should already be targeting your primary foreclosure cleanup client base via email, snail-mail, phone, and through your online marketing efforts. But, keeping in mind your primary focus of making money TODAY, if your price is right, you will be busier than you can shake a stick at with just lawn care — and you will come home with that $300 bucks in your pocket!

Plan of Action Example: If you specialize in interior cleanup, get on the phone and plan to call 500 realtors today. Yes, it will be a lot of calls, and you may not make it through even a quarter of the list, but if your Today Only Special is low enough, and you strategically target your list, you will get cleanup business. Always remember that business is simply a numbers game: the more prospects you target, the more business you will get.

If you want to specialize in exterior cleanup and you know the dump yard only charges you $37 for exterior debris dumping, call 200 real estate brokers and offer an incredible Weekend Only deal on exterior debris removal to the broker’s list of realtors. Make it a special they can’t refuse and see what positive results you have.

Greasing the Pipes: Remember, as a business owner, you must concentrate on how you can make money TODAY to survive. All the while you will be greasing the pipes (a term my multi-million dollar small business mentor used quite often) for future foreclosure cleaning business.

Many wishes of great success in your foreclosure cleanup business!