If you want virtual port support then specify the port as "0". This causes Squid to forward the request to this server irregardles of what any redirectors or Host headers says. Leave this at off if you have multiple backend servers, and use a redirector or host table or private DNS to map the requests to the appropriate backend servers.
Note that the mapping needs to be a mapping between requested and backend from redirector domain names or caching will fail, as cacing is performed using the URL returned from the redirector.
Squid can be an accelerator for different HTTP servers by looking at this header. We recommend that this option remain disabled unless you are sure of what you are doing. However, you will need to enable this option if you run Squid as a transparent proxy.
Otherwise, virtual servers which require the Host: header will not be properly cached. The default is 10, which will rotate with extensions 0 through 9. This will enable you to rename the logfiles yourself just before sending the rotate signal. Note, the 'squid -k rotate' command normally sends a USR1 signal to the running squid process.
In certain situations e. Probably just as easy to change your kernel's default. Set to zero to use the default buffer size. Make this a "mailto" URL to your admin address, or maybe just a link to your organizations Web page. To include this in your error messages, you must rewrite the error template files found in the "errors" directory.
If memory is a premium on your system and you believe your malloc library outperforms Squid routines, disable this. All free requests that exceed this limit will be handled by your malloc library. Squid does not pre-allocate any memory, just safe-keeps objects that otherwise would be free d. If not set default or set to zero, Squid will keep all memory it can.
That is, there will be no limit on the total amount of memory used for safe-keeping. An overhead for maintaining memory pools is not taken into account when the limit is checked. This overhead is close to four bytes per object kept. By default it looks like this: X-Forwarded-For: If you have sibling relationships with caches in other administrative domains, this should be 'off'.
If you only have sibling relationships with caches under your control, then it is probably okay to set this to 'on'. To disable an action, set the password to "disable". To allow performing an action without a password, set the password to "none". Use the keyword "all" to set the same password for all actions. The default is 13 KB. Lowering this value increases the total number of buckets and also the storage maintenance rate.
These are counts, not percents. The defaults are and When the high water mark is reached, database entries will be deleted until the low mark is reached. There will be at least this much delay between successive pings to the same network. The default is five minutes. If your peer has configured Squid during compilation with '--enable-icmp' then that peer will send ICMP pings to origin server sites of the URLs it receives.
Then, when choosing a parent cache, Squid will choose the parent with the minimal RTT to the origin server. When this happens, the hierarchy field of the access. This option is off by default. By default they will be unbuffered.
Buffering them can speed up the writing slightly though you are unlikely to need to worry. This option may be disabled by using --disable-http-violations with the configure script. For example, to always directly forward requests for local servers use something like: acl local-servers dstdomain my.
You may need to use a deny rule to exclude a more-specific case of some other rule. Example: acl local-external dstdomain external. For example, to force the use of a proxy for all requests, except those in your local domain use something like: acl local-servers dstdomain foo.
You may now specify exactly which headers are to be allowed, or which are to be removed from outgoing requests. There are two methods of using this option. You may either allow specific headers thus denying all others , or you may deny specific headers thus allowing all others. By default, all headers are allowed no anonymizing is performed. Use this to fake one up. When a connection to a host is initiated, and that host has several IP addresses, the default connection timeout is reduced by dividing it by the number of addresses.
So, a site with 15 addresses would then have a timeout of 8 seconds for each address attempted. To avoid having the timeout reduced to the point where even a working host would not have a chance to respond, this setting is provided. The default value is three tries, the not recommended maximum is tries.
A warning message will be generated if it is set to a value greater than ten. By default it listens to port on the machine. If you don't wish to use SNMP, set this to "0".
All access to the agent is denied by default. If you're using that version of IOS, change this value to 3. Do NOT use this option if you're unsure how many interfaces you have, or if you know you have only one interface. For example, if you have one class 2 delay pool and one class 3 delays pool, you have a total of 2 delay pools. To enable this option, you must use --enable-delay-pools with the configure script. The first matched delay pool is always used, i.
I can't even believe you are reading this. Are you crazy? A value of 0 indicates no limit. Options: strip: The whitespace characters are stripped out of the URL. This is the behavior recommended by RFC The user receives an "Invalid Request" message. The whitespace characters remain in the URI. Note the whitespace is passed to redirector processes if they are in use.
Whenever the cache answers a customer request, that means the request did not need to be answered by your website origin server. Having a large percentage of cache hits results in performance benefits and reduced costs. From a cost-savings perspective, every request that receives a response from cache does not need to connect to your origin server, greatly reducing load.
With a finely-tuned caching configuration, your origin only needs to respond to requests for personalized actions such as checkout and and account pages. 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 server, 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 when the system boots up, 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 server. 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. To be able to restart Squid, damaged caches must be deleted.
Removing Squid from the system does not remove the cache hierarchy and log files. Setting up a local DNS server makes sense even if it does not manage its own domain. It then simply acts as a caching-only name server and is also able to resolve DNS requests via the root name servers without requiring any special configuration see Section How this can be done depends on whether you chose dynamic DNS during the configuration of the Internet connection.
This way, Squid can always find the local name server when it starts. With static DNS, no automatic DNS adjustments take place while establishing a connection, so there is no need to change any sysconfig variables. Defines settings in regard to cache memory, maximum and minimum object size, and more.
Define paths to access, cache, and cache store log files in addition with connection timeouts and client lifetime. To start Squid for the first time, no changes are necessary in this file, but external clients are initially denied access. The proxy is available for localhost. The default port is Many entries are commented and therefore begin with the comment character. The relevant specifications can be found at the end of the line. The given values usually correlate with the default values, so removing the comment signs without changing any of the parameters usually has no effect.
If possible, leave the commented lines as they are and insert the options along with the modified values in the line below. This way, the default values may easily be recovered and compared with the changes. Sometimes, Squid options are added, removed, or modified. Therefore, if you try to use the old squid. The following is a list of a selection of configuration options for Squid.
It provides a distributed in-memory database with an extensive command set that supports many common scenarios. These are described later in this document, in the section Using Redis caching. This section summarizes some of the key features that Redis provides.
Redis supports both read and write operations. In Redis, writes can be protected from system failure either by being stored periodically in a local snapshot file or in an append-only log file.
This is not the case in many caches which should be considered transitory data stores. All writes are asynchronous and do not block clients from reading and writing data. When Redis starts running, it reads the data from the snapshot or log file and uses it to construct the in-memory cache.
For more information, see Redis persistence on the Redis website. Redis does not guarantee that all writes will be saved in the event of a catastrophic failure, but at worst you might lose only a few seconds worth of data.
Remember that a cache is not intended to act as an authoritative data source, and it is the responsibility of the applications using the cache to ensure that critical data is saved successfully to an appropriate data store. For more information, see the Cache-aside pattern. Redis is a key-value store, where values can contain simple types or complex data structures such as hashes, lists, and sets. It supports a set of atomic operations on these data types.
Keys can be permanent or tagged with a limited time-to-live, at which point the key and its corresponding value are automatically removed from the cache.
For more information about Redis keys and values, visit the page An introduction to Redis data types and abstractions on the Redis website. Write operations to a Redis primary node are replicated to one or more subordinate nodes. Read operations can be served by the primary or any of the subordinates. In the event of a network partition, subordinates can continue to serve data and then transparently resynchronize with the primary when the connection is reestablished.
For further details, visit the Replication page on the Redis website. Redis also provides clustering, which enables you to transparently partition data into shards across servers and spread the load.
This feature improves scalability, because new Redis servers can be added and the data repartitioned as the size of the cache increases. This ensures availability across each node in the cluster. For more information about clustering and sharding, visit the Redis cluster tutorial page on the Redis website.
A Redis cache has a finite size that depends on the resources available on the host computer. When you configure a Redis server, you can specify the maximum amount of memory it can use. You can also configure a key in a Redis cache to have an expiration time, after which it is automatically removed from the cache.
This feature can help prevent the in-memory cache from filling with old or stale data. As memory fills up, Redis can automatically evict keys and their values by following a number of policies.
The default is LRU least recently used , but you can also select other policies such as evicting keys at random or turning off eviction altogether in which, case attempts to add items to the cache fail if it is full. Redis enables a client application to submit a series of operations that read and write data in the cache as an atomic transaction.
All the commands in the transaction are guaranteed to run sequentially, and no commands issued by other concurrent clients will be interwoven between them. However, these are not true transactions as a relational database would perform them. Transaction processing consists of two stages--the first is when the commands are queued, and the second is when the commands are run. During the command queuing stage, the commands that comprise the transaction are submitted by the client. If some sort of error occurs at this point such as a syntax error, or the wrong number of parameters then Redis refuses to process the entire transaction and discards it.
During the run phase, Redis performs each queued command in sequence. If a command fails during this phase, Redis continues with the next queued command and does not roll back the effects of any commands that have already been run.
This simplified form of transaction helps to maintain performance and avoid performance problems that are caused by contention. Redis does implement a form of optimistic locking to assist in maintaining consistency.
For detailed information about transactions and locking with Redis, visit the Transactions page on the Redis website. Redis also supports nontransactional batching of requests. The Redis protocol that clients use to send commands to a Redis server enables a client to send a series of operations as part of the same request.
This can help to reduce packet fragmentation on the network. When the batch is processed, each command is performed. If any of these commands are malformed, they will be rejected which doesn't happen with a transaction , but the remaining commands will be performed.
There is also no guarantee about the order in which the commands in the batch will be processed. Redis is focused purely on providing fast access to data, and is designed to run inside a trusted environment that can be accessed only by trusted clients. Redis supports a limited security model based on password authentication. It is possible to remove authentication completely, although we don't recommend this.
All authenticated clients share the same global password and have access to the same resources. If you need more comprehensive sign-in security, you must implement your own security layer in front of the Redis server, and all client requests should pass through this additional layer. Redis should not be directly exposed to untrusted or unauthenticated clients. You can restrict access to commands by disabling them or renaming them and by providing only privileged clients with the new names.
Redis does not directly support any form of data encryption, so all encoding must be performed by client applications. Additionally, Redis does not provide any form of transport security. If you need to protect data as it flows across the network, we recommend implementing an SSL proxy. For more information, visit the Redis security page on the Redis website. Azure Cache for Redis provides its own security layer through which clients connect.
The underlying Redis servers are not exposed to the public network. Azure Cache for Redis provides access to Redis servers that are hosted at an Azure datacenter.
You can provision a cache by using the Azure portal. The portal provides a number of predefined configurations. Using the Azure portal, you can also configure the eviction policy of the cache, and control access to the cache by adding users to the roles provided. These roles, which define the operations that members can perform, include Owner, Contributor, and Reader.
For example, members of the Owner role have complete control over the cache including security and its contents, members of the Contributor role can read and write information in the cache, and members of the Reader role can only retrieve data from the cache. Most administrative tasks are performed through the Azure portal. For this reason, many of the administrative commands that are available in the standard version of Redis are not available, including the ability to modify the configuration programmatically, shut down the Redis server, configure additional subordinates, or forcibly save data to disk.
The Azure portal includes a convenient graphical display that enables you to monitor the performance of the cache. For example, you can view the number of connections being made, the number of requests being performed, the volume of reads and writes, and the number of cache hits versus cache misses.
Using this information, you can determine the effectiveness of the cache and if necessary, switch to a different configuration or change the eviction policy. Additionally, you can create alerts that send email messages to an administrator if one or more critical metrics fall outside of an expected range. For example, you might want to alert an administrator if the number of cache misses exceeds a specified value in the last hour, because it means the cache might be too small or data might be being evicted too quickly.
For further information and examples showing how to create and configure an Azure Cache for Redis, visit the page Lap around Azure Cache for Redis on the Azure blog. If you're building ASP. The session state provider for Azure Cache for Redis enables you to share session information between different instances of an ASP.
NET web application, and is very useful in web farm situations where client-server affinity is not available and caching session data in-memory would not be appropriate.
Using the session state provider with Azure Cache for Redis delivers several benefits, including:. For more information, see ASP. NET applications that run outside of the Azure environment.
The latency of accessing the cache from outside of Azure can eliminate the performance benefits of caching data. NET web application. Using the output cache provider with Azure Cache for Redis can improve the response times of applications that render complex HTML output. Application instances that generate similar responses can use the shared output fragments in the cache rather than generating this HTML output afresh.
If you require an advanced configuration that is not covered by the Azure Redis cache such as a cache bigger than 53 GB you can build and host your own Redis servers by using Azure virtual machines. This is a potentially complex process because you might need to create several VMs to act as primary and subordinate nodes if you want to implement replication.
Furthermore, if you wish to create a cluster, then you need multiple primaries and subordinate servers. However, each set of pairs can be running in different Azure datacenters located in different regions, if you wish to locate cached data close to the applications that are most likely to use it. If you implement your own Redis cache in this way, you are responsible for monitoring, managing, and securing the service. Partitioning the cache involves splitting the cache across multiple computers.
This structure gives you several advantages over using a single cache server, including:. For a cache, the most common form of partitioning is sharding. In this strategy, each partition or shard is a Redis cache in its own right.
Data is directed to a specific partition by using sharding logic, which can use a variety of approaches to distribute the data. The Sharding pattern provides more information about implementing sharding. The page Partitioning: how to split data among multiple Redis instances on the Redis website provides further information about implementing partitioning with Redis. Redis supports client applications written in numerous programming languages.
If you are building new applications by using the. Redis client library. This library provides a. NET Framework object model that abstracts the details for connecting to a Redis server, sending commands, and receiving responses. It is available in Visual Studio as a NuGet package. To connect to a Redis server you use the static Connect method of the ConnectionMultiplexer class.
The connection that this method creates is designed to be used throughout the lifetime of the client application, and the same connection can be used by multiple concurrent threads. Do not reconnect and disconnect each time you perform a Redis operation because this can degrade performance. You can specify the connection parameters, such as the address of the Redis host and the password. If you are using Azure Cache for Redis, the password is either the primary or secondary key that is generated for Azure Cache for Redis by using the Azure portal.
After you have connected to the Redis server, you can obtain a handle on the Redis database that acts as the cache. The Redis connection provides the GetDatabase method to do this.
You can then retrieve items from the cache and store data in the cache by using the StringGet and StringSet methods. These methods expect a key as a parameter, and return the item either in the cache that has a matching value StringGet or add the item to the cache with this key StringSet. Depending on the location of the Redis server, many operations might incur some latency while a request is transmitted to the server and a response is returned to the client.
The StackExchange library provides asynchronous versions of many of the methods that it exposes to help client applications remain responsive. These methods support the Task-based Asynchronous pattern in the.
NET Framework. The following code snippet shows a method named RetrieveItem.
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