Preface
Squid proxy server enables you to cache your web content and return it quickly on subsequent requests. System administrators often struggle with delays and too much bandwidth being used, but Squid solves these problems by handling requests locally. By deploying Squid in accelerator mode, requests are handled faster than on normal web servers, thus making your site perform quicker than everyone else's!
The Squid Proxy Server 3.1 Beginner's Guide will help you to install and configure Squid so that it is optimized to enhance the performance of your network. Caching usually takes a lot of professional know-how, which can take time and be very confusing. The Squid proxy server reduces the amount of effort that you will have to spend and this book will show you how best to use Squid, saving your time and allowing you to get most out of your network.
Whether you only run one site, or are in charge of a whole network, Squid is an invaluable tool which improves performance immeasurably. Caching and performance optimization usually requires a lot of work on the developer's part, but Squid does all that for you. This book will show you how to get the most out of Squid by customizing it for your network. You will learn about the different configuration options available and the transparent and accelerated modes that enable you to focus on particular areas of your network.
Applying proxy servers to large networks can be a lot of work as you have to decide where to place restrictions and who to grant access. However, the straightforward examples in this book will guide you through step-by-step so that you will have a proxy server that covers all areas of your network by the time you finish reading.
What this book covers
Chapter 1, Getting Started with Squid, discusses the basics of proxy servers and web caching and how we can utilize them to save bandwidth and improve the end user's browsing experience. We will also learn to identify the correct Squid version for our environment. We will explore various configuration options available for enabling or disabling certain features while we compile Squid from the source code. We will explore steps to compile and install Squid.
Chapter 2, Configuring Squid, explores the syntax used in the Squid configuration file, which is used to control Squid's behavior. We will explore the important directives used in the configuration file and will see related examples to understand them better. We will have a brief overview of the powerful access control lists which we will learn in detail in later chapters. We will also learn to fine-tune our cache to achieve a better HIT ratio to save bandwidth and reduce the average page load time.
Chapter 3, Running Squid, talks about running Squid in different modes and various command line options available for debugging purposes. We will also learn about rotating Squid logs to reclaim disk space by deleting old/obsolete log files. We will learn to install the init script to automatically start Squid on system startup.
Chapter 4, Getting Started with Squid's Powerful ACLs and Access Rules, explores the Access Control Lists in detail with examples. We will learn about various ACL types and to construct ACLs to identify requests and responses based on different criteria. We will also learn about mixing ACLs of various types with access rules to achieve desired access control.
Chapter 5, Understanding Log Files and Log Formats, discusses configuring Squid to generate customized log messages. We will also learn to interpret the messages logged by Squid in various log files.
Chapter 6, Managing Squid and Monitoring Traffic, explores the Squid's Cache Manager web interface in this chapter using which we can monitor our Squid proxy server and get statistics about different components of Squid. We will also have a look at a few log file analyzers which make analyzing traffic simpler compared to manually interpreting the access log messages.
Chapter 7, Protecting your Squid with Authentication, teaches us to protect our Squid proxy server with authentication using the various authentication schemes available. We will also learn to write custom authentication helpers using which we can build our own authentication system for Squid.
Chapter 8, Building a Hierarchy of Squid Caches, explores cache hierarchies in detail. We will also learn to configure Squid to act as a parent or a sibling proxy server in a hierarchy, and to use other proxy servers as a parent or sibling cache.
Chapter 9, Squid in Reverse Proxy Mode, discusses how Squid can accept HTTP requests on behalf of one or more web servers in the background. We will learn to configure Squid in reverse proxy mode. We will also have a look at a few example scenarios.
Chapter 10, Squid in Intercept Mode, talks about the details of intercept mode and how to configure the network devices, and the host operating system to intercept the HTTP requests and forward them to Squid proxy server. We will also have a look at the pros and cons of Squid in intercept mode.
Chapter 11, Writing URL Redirectors and Rewriters. Squid's behavior can be further customized using the URL redirectors and rewriter helpers. In this chapter, we will learn about the internals of redirectors and rewriters and we will create our own custom helpers.
Chapter 12, Troubleshooting Squid, discusses some common problems or errors which you may come across while configuring or running Squid. We will also learn about getting online help to resolve issues with Squid and filing bug reports.
What you need for this book
A beginner level knowledge of Linux/Unix operating system and familiarity with basic commands is all what you need. Squid runs almost on all Linux/Unix operating systems and there is a great possibility that your favorite operating system repository already has Squid.
On a server, the availability of free main memory and speed of hard disk play a major role in determining the performance of the Squid proxy server. As most of the cached objects stay on the hard disks, faster disks will result in low disk latency and faster responses. But faster hard disks (SCSI) are often very expensive as compared to ATA hard disks and we have to analyze our requirements to strike a balance between the disk speed we need and the money we are going to spend on it.
The main memory is the most important factor for optimizing Squid's performance. Squid stores a little bit of information about each cached object in the main memory. On average, Squid consumes up to 32 MB of the main memory for every GB of disk caching. The actual memory utilization may vary depending on the average object size, CPU architecture, and the number of concurrent users, and so on. While memory is critical for good performance, a faster CPU also helps, but is not really critical.
Who this book is for
If you are a Linux or Unix system administrator and you want to enhance the performance of your network or you are a web developer and want to enhance the performance of your website, this book is for you. You will be expected to have some basic knowledge of networking concepts, but may not have used caching systems or proxy servers until now.
Conventions
In this book, you will find several headings appearing frequently. To give clear instructions of how to complete a procedure or task, we use:
Time for action - heading
Action 1
Action 2
Action 3
Instructions often need some extra explanation so that they make sense, so they are followed with:
What just happened?
This heading explains the working of tasks or instructions that you have just completed.
You will also find some other learning aids in the book, including:
Pop quiz
These are short multiple choice questions intended to help you test your own understanding.
Have a go hero - heading
These set practical challenges and give you ideas for experimenting with what you have learned.
You will also find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.
Code words in text are shown as follows: "The directive visible_hostname is used to set the hostname."
A block of code is set as follows:
acl special_network src 192.0.2.0/24 tcp_outgoing_address 198.51.100.25 special_network tcp_outgoing_address 198.51.100.86
Any command-line input or output is written as follows:
$ mkdir /drive/squid_cache
New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "If we click on the Internal DNS Statistics link in the Cache Manager menu, we will be presented with various statistics about the requests performed by the internal DNS client".
Note
Warnings or important notes appear in a box like this.
Note
Tips and tricks appear like this.
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