It is also possible to configure cache hierarchies, so a cache can forward object requests to sibling caches or to a parent cache—causing it to request objects from another cache in the local network or directly from the source. Choosing the appropriate topology for the cache hierarchy is very important, because it is not desirable to increase the overall traffic on the network.
For a very large network, it would make sense to configure a proxy server for every subnet and connect them to a parent proxy, which in turn is connected to the proxy cache of the ISP. To find the most appropriate server from which to request objects, a cache sends an ICP request to all sibling proxies.
The sibling proxies answer these requests via ICP responses. If multiple HIT responses were found, the proxy server decides from which server to download, depending on factors such as which cache sent the fastest answer or which one is closer. If no satisfactory responses are received, the request is sent to the parent cache. The more objects maintained in the network, the greater the possibility of finding the desired one. Objects like these are not cached because they change each time they are accessed.
To determine how long objects should remain in the cache, objects are assigned one of several states. Other headers specifying that objects must not be cached can be used as well.
Objects in the cache are normally replaced, because of a lack of free disk space, using algorithms such as LRU last recently used.
This means that the proxy expunges those objects that have not been requested for the longest time. System requirements largely depend on the maximum network load that the system must bear. Therefore, examine load peaks, as during those times, load might be more than four times the day's average. When in doubt, slightly overestimate the system's requirements. Having Squid working close to the limit of its capabilities can lead to a severe loss in quality of service.
The following sections point to system factors in order of significance:. The amount of memory RAM required by Squid directly correlates with the number of objects in the cache. Therefore, it is very important to have sufficient memory for the Squid process, because system performance is dramatically reduced if the swap disk is used.
Squid also stores cache object references and frequently requested objects in the main memory to speed up retrieval of this data. In addition to that, there is other data that Squid needs to keep in memory, such as a table with all the IP addresses handled, an exact domain name cache, the most frequently requested objects, access control lists, buffers, and more. Squid is tuned to work best with lower processor core counts 4—8 physical cores , with each providing high performance.
Technologies providing virtual cores such as hyperthreading can hurt performance. To make the best use of multiple CPU cores, it is necessary to set up multiple worker threads writing to different caching devices. By default, multi-core support is mostly disabled. In a small cache, the probability of a HIT finding the requested object already located there is small, because the cache is easily filled and less requested objects are replaced by newer ones.
If, for example, 1 GB is available for the cache and the users use up only 10 MB per day surfing, it would take more than one hundred days to fill the cache. The easiest way to determine the necessary cache size is to consider the maximum transfer rate of the connection. If all this traffic ended up in the cache, in one hour it would add up to MB. Assuming that all this traffic is generated in only eight working hours, it would reach 3.
Because the connection is normally not used to its upper volume limit, it can be assumed that the total data volume handled by the cache is approximately 2 GB. Hence, in this example, 2 GB of disk space is required for Squid to keep one day's worth of browsing data cached. Speed plays an important role in the caching process, so this factor deserves special attention. For use as a proxy, hard disks with high rotation speeds or SSDs are the best choice.
When using hard disks, it can be better to use multiple smaller hard disks, each with a single cache directory to avoid excessive read times. Using a RAID system allows increasing reliability at expense of speed. However, for performance reasons, avoid software RAID5 and similar settings. File system choice is usually not decisive.
However, using the mount option noatime can improve performance—Squid provides its own time stamps and thus does not need the file system to track access times. If not already installed, install the package squid. To ensure a smooth start-up, the network should be configured in a way that at least one name server and the Internet can be reached.
Problems can arise if a dial-up connection is used with a dynamic DNS configuration. If you want Squid to start together with the system, enable the service with systemctl enable squid. The output of this command should indicate that Squid is loaded and active running. The output of this command should be 0 , but may contain additional warnings or messages. To test the functionality of Squid on the local system, choose one of the following ways:. To test, you can use squidclient , a command-line tool that can output the response to a Web request, similar to wget or curl.
Unlike those tools, squidclient will automatically connect to the default proxy setup of Squid, localhost However, if you changed the configuration of Squid, you need to configure squidclient to use different settings using command line options.
For more information, see squidclient --help. The output shown in Example The example above contains two X-Cache lines. You can ignore the first X-Cache header. It is produced by the internal caching software of the originating Web server.
Using a browser: Set up localhost as the proxy and as the port. You can then load a page and check the response headers in the Network panel of the browser's Inspector or Developer Tools. The headers should be reproduced similarly to the way shown in Example However, in doing so, consider that Squid is made completely accessible to anyone by this action.
Therefore, define ACLs access control lists that control access to the proxy. After modifying the configuration file, Squid must be reloaded or restarted. For more information on ACLs, see Section Terminating Squid with kill or killall can damage the cache. For more in-depth configuration of Squid, see the References section. Prior to editing the configuration file, you should make a copy of the original file and protect it from writing so you will have the original settings as a reference, and to re-use as necessary.
Make this copy and protect it from writing using the following commands:. In this example it is set to weezie. Share 1. Tweet 0. Share 0. Hi, How do I add multiple proxy servers? Hi, very good article. Many thanks, Best regards,. Leave a Reply Cancel reply Your email address will not be published.
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Second, enter the IP address and the netmask to which these clients send their requests. In this example, Web services port 80 are redirected to the proxy port port If there are more networks or services to add, they must be separated by a blank space in the respective entry. Start Squid as shown in Section To verify that all ports are correctly configured, perform a port scan on the machine from any computer outside your network.
Only the Web services port 80 should be open. The cache manager cachemgr. It is also a more convenient way to manage the cache and view statistics without logging the server. First, a running Web server on your system is required. To check if Apache is already running, as root enter the command rcapache status. If a message like this appears:. Apache is running on the machine. The last step to set it up is to copy the file cachemgr. For bit, this works as follows:.
In a bit environment, the file cachemgr. There are some default settings in the original file required for the cache manager.
These rules assume that the Web server and Squid are running on the same machine. If the communication between the cache manager and Squid originates at the Web server on another computer, include an extra ACL as in Example Then add the rules in Example Configure a password for the manager for access to more options, like closing the cache remotely or viewing more information about the cache.
Restart Squid every time the configuration file is changed. Do this easily with rcsquid reload. Press continue and browse through the different statistics. This section is not intended to explain an extensive configuration of squidGuard, only to introduce it and give some advice for using it.
It lets you define multiple access rules with different restrictions for different user groups on a Squid cache. Before it can be used, install squidGuard. Experiment later with more complicated configuration settings. Using Apache is strongly recommended. Now, configure Squid to use squidGuard. The more processes you set, the more RAM is required. Try low numbers e.
Last, have Squid load the new configuration by running rcsquid reload. Now, test your settings with a browser. It works with native Squid access log files. Log in as root then enter cat access. It is important when piping more than one log file that the log files are chronologically ordered with older files first. These are some options of the program:. If you have multiple similar files like access. To solve this issue, you may use the syntax access.
More information about the various options can be found in the program's manual page with man calamaris. This puts the report in the directory of the Web server. Apache is required to view the reports. In addition, mailing lists are available for Squid at squid-users squid-cache. Contents Contents. Warning: Terminating Squid Terminating Squid with kill or killall can damage the cache.
Otherwise it adds a line to the header like X-Forwarded-For: The following are some simple examples: acl mysurfers srcdomain. All clients must use a proxy, regardless of whether they are aware of it.
Example Which accesses to services should be redirected to a local port on the firewall machine? This option can be used to force all internal users to surf via your squid proxy, or transparently redirect incoming webtraffic to a secure webserver. Checking for service httpd: OK Server uptime: 1 day 18 hours 29 minutes 39 seconds. Block access to some listed or blacklisted Web servers or URLs for some users. Block access to URLs matching a list of regular expressions or words for some users.
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