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What is caching or content caching?

Caching (or content caching) is a widely used technology that stores copies of data in temporary storage locations (also known as caches), so that data can be accessed easily and quickly compared to retrieving data from the original storage. Depending on the type and purpose of the cache, the data stored in the cache may include files or file fragments (such as HTML files, scripts, images, documents, etc.), database operations or records, API calls, DNS records, and so on.

Caching can be in the form of hardware or software. Software-based caching, which is the focus of this article, can be implemented at different layers of the application stack.

Caching can be imposed on the client side (or in the application presentation layer), such as browser caching or cached applications (or offline mode). Most, if not all, modern browsers come with an implementation of HTTP caching. You may have heard the popular phrase "clear cache" when you visit a Web application to enable you to view the latest data or content on a Web site or application, rather than when the browser uses old copies of locally stored content.

Another example of client caching is DNS caching, which occurs at the operating system (OS) level. It is a temporary store of DNS lookup information about previous operating systems or Web browsers.

Caching can also be implemented at the network level in LAN or WAN through proxies. A common example of such caching is CDN (content delivery Network), which is a globally distributed network of Web proxy servers.

Third, you can also implement caching on the source server or back-end server. Server-level caching takes different forms, including:

Web server cache (for caching images, documents, scripts, etc.).

Application caching or memory (used to read files from disk, read data from other services or processes, request data from API, etc.).

Database caching (provides in-memory access to commonly used data, such as requested database rows, query results, and other operations).

Note that cached data can be stored on any storage system, including databases, files, system memory, etc., but it should be faster than the main source. In this respect, memory caching is the most efficient and commonly used form of caching.

Why use caching?

Caching has many advantages, including:

At the database level, it improves the read performance of cached data to microseconds. You can also use writeback caching to improve write performance, in which case the data is written to memory at specified intervals and then to disk or primary storage. But its data integrity can have a catastrophic impact. For example, when the system crashes before the data is committed to the main storage. At the application level, caching can store frequently read data in the application process itself, reducing data lookup time from a few seconds to a few microseconds, especially on the network. Caching helps reduce server load, latency, and network bandwidth, given the performance of the entire application and server, because cached data is provided to the client, thereby improving response time and delivery speed to the client. Caching also allows content availability (especially through CDN), as well as many other benefits.

1. Redis

Redis (full REmote DIctionary Server) is a free, open source, fast, high-performance, flexible distributed memory computing system that can be used in most, if not all, programming languages.

It is a data structure store in memory, used as a cache engine, a persistent disk database in memory, and a message broker. Although Redis is developed and tested on Linux (the recommended deployment platform) and OS X, it can also run on other POSIX systems (such as * BSD) without any external dependencies.

Redis supports many data structures, such as strings, hashes, lists, collections, sorted collections, bitmaps, streams, etc. This allows programmers to use specific data structures to solve specific problems. It supports automatic operations on its data structures, such as appending to strings, pushing elements to lists, increasing hashes, calculating set intersections, and so on.

Its main features include Redis master-slave replication (asynchronous by default), using the high availability and automatic failover provided by Redis Sentinel, Redis clustering (you can scale horizontally by adding more cluster nodes), and data partitioning (distributing data among multiple Redis instances). It also has support for transactions, Lua scripting, a range of persistence options, and client-server communication encryption.

As a disk database that can be persisted in memory, Redis works best with in-memory datasets. However, you can use it with disk databases, such as MySQL,PostgreSQL, and so on. For example, you can get a lot of small data for write operations in Redis and keep other blocks in the disk database.

Redis supports security in a number of ways: one is to use the protected Mode feature to protect Redis instances from external network access. It also supports client-server authentication (configuring passwords in the server and providing passwords in the client) and TLS on all communication channels (such as client connections, replication links, Redis Cluster bus protocols, etc.).

Redis has many use cases, including database caching, full-page caching, user session data management, API response storage, publish / subscribe messaging systems, message queues, and so on. These can be applied to games, social networking applications, RSS feeds, real-time data analysis, user recommendations, etc.

2. Memcached

Memcached is a free, open source, simple but powerful distributed memory object caching system. It is a key-value store in memory that stores a small amount of data, such as the results of database calls, API calls, or page rendering. It can run on Unix-like operating systems, including Linux and OS X, or on Microsoft Windows.

As a developer tool, it is designed to increase the speed of dynamic Web applications by caching content (least recently used (LRU) cache by default), thereby reducing the database load on disk-it acts as a short-term memory application for the following tasks. It provides API, the most popular programming language.

Memcached supports strings as the only data type. It has a client-server architecture, half of which takes place on the client side and the other half on the server side. It is important that the customer knows how to select a server to write or read for the project. In addition, if the client cannot connect to the server, the client knows exactly what to do.

Although it is a distributed caching system and therefore supports clustering, Memcached servers are disconnected from each other (that is, they do not know each other). This means that there is no replication support like Redis. They also know how to store and retrieve projects and manage when to expel or reuse memory. You can increase available memory by adding more servers.

Starting with Memcached 1.5.13, it supports authentication and encryption through TLS, but this feature is still in the experimental stage.

3. Apache Ignite

Apache Ignite, also a free open source, horizontally scalable distributed in-memory key storage, cache and multi-model database system, provides powerful processing API that can be used for computing on distributed data. It is also an in-memory data grid that can be used in memory or with Ignite native persistence. It can run on systems like UNIX, such as Linux and Windows.

It has multi-tier storage, complete SQL support and ACID (atomicity, consistency, isolation, durability) transactions across multiple cluster nodes (supported only at the key API level), co-location processing and machine learning. It supports automatic integration with any third-party database, including any RDBMS (such as MySQL,PostgreSQL,Oracle database, etc.) or NoSQL storage.

It is important to note that although Ignite is used as an SQL data store, it is not entirely a SQL database. Compared with traditional databases, it can obviously deal with constraints and indexes. It supports primary and secondary indexes, but only the primary index is used to enforce uniqueness. In addition, it does not support foreign key constraints.

Ignite also supports security by allowing you to enable authentication on the server and provide user credentials on the client. SSL socket communication is also supported to provide secure connections between all Ignite nodes.

Ignite has many use cases, including caching systems, system workload acceleration, real-time data processing and analysis. It can also be used as a graphics-centric platform.

4.Couchbase Server

Couchbase Server is also an open source, distributed, NoSQL document-oriented participating database that stores data as projects in key-value format. It runs on Linux and other operating systems such as Windows and Mac OS X. It uses the rich document-oriented query language N1QL, which provides powerful query and indexing services to support sub-millisecond operations on data.

Its remarkable features are fast key storage with managed cache dedicated indexer powerful query engine scale-out architecture (multi-dimensional extension) big data and SQL integration full-stack security and high availability.

Couchbase Server comes with native multi-instance cluster support, where the cluster manager tool coordinates all node activities and provides only cluster-wide interfaces to clients. Importantly, you can add, remove, or replace nodes as needed without downtime. It also supports data replication across cluster nodes and selective data replication across data centers.

It uses dedicated Couchbase server ports, different authentication mechanisms (using credentials or certificates), role-based access control (to check each authenticated user to check the system-defined roles assigned to them), auditing, logs and sessions, and security through TLS.

Its use cases include a unified programming interface, full-text search, parallel query processing, document management, indexing and so on. It is designed to provide low latency data management for large interactive Web, mobile and IoT applications.

5.Hazelcast IMDG

Hazelcast IMDG (in-memory data Grid) is an open source, lightweight, fast and scalable in-memory data grid middleware that provides flexible and scalable distributed in-memory computing. Hazelcast IMDG can also run on Linux,Windows and Mac OS X, as well as on any other platform on which Java is installed. It supports various flexible language native data structures, such as Map,Set,List,MultiMap,RingBuffer and HyperLogLog.

Hazelcast is peer-to-peer, supports simple scalability, cluster settings (with options for collecting statistics, monitoring through JMX protocol, and managing clusters using useful utilities), distributed data structures and events, data allocation and transaction capabilities. This is also redundant because it keeps a backup of each data entry on multiple members. To expand the cluster, simply start another instance, and the data and backups are automatically and evenly balanced.

It provides a useful set of API to access the CPU in the cluster for maximum processing speed. It also provides distributed implementation of a large number of developer-friendly interfaces from Java, such as Map,Queue,ExecutorService,Lock and JCache.

Its security features include cluster member and client authentication, as well as access control checks for client operations through JAAS-based security features. It also allows you to intercept socket connections and remote operations performed by clients, encrypt socket-level communication between cluster members, and enable SSL / TLS socket communication. But according to official documentation, most of these security features are provided in the enterprise version.

Its most popular use cases are caching and data storage in distributed memory. However, it can also be deployed for Web session clustering, NoSQL replacement, parallel processing, simple messaging, and more.

6.Mcrouter

Mcrouter is a free open source Memcached protocol router used to extend Memcached deployments developed and maintained by Facebook. It has the functions of Memcached ASCII protocol, flexible routing, multi-cluster support, multi-level cache, connection pool, multiple hash schemes, prefix routing, replication pool, production traffic shadow, online reconfiguration and target health monitoring / automatic failover.

In addition, it supports cold cache warm-up, rich statistics and debugging commands, reliable delete stream quality of service, large values, broadcast operations, and IPv6 and SSL support.

It has been used as a core component of the cache infrastructure in Facebook and Instagram, processing nearly 5 billion requests per second at peak times.

7.Varnish Cache

Varnish Cache is an open source flexible, modern and versatile Web application accelerator located between the Web client and the original server. It runs on all modern Linux,FreeBSD and Solaris (x86 only) platforms. It is an excellent caching engine and content accelerator that you can deploy in front of Web servers such as NGINX,Apache to listen on the default HTTP port to receive client requests and forward them to the Web server and deliver the Web server response client.

While acting as an intermediary between the client and the original server, Varnish Cache provides many benefits, the basic element of which is caching Web content in memory to reduce the load on the Web server and increase delivery speed to the client.

After receiving the HTTP request from the client, it forwards the request to the back-end Web server. After the Web server responds, Varnish caches the content in memory and passes the response to the client. When a client requests the same content, Varnish will serve it from the cache promotion application response. If it cannot provide the contents of the cache, the request is forwarded to the back end, and then the response is cached and passed to the client.

Varnish has VCL (Varnish configuration language, a flexible domain-specific language) for configuring how requests are handled and the Varnish module (VMODS), which is an extension of Varnish Cache.

In terms of security, Varnish Cache supports logging, request checking and restrictions, authentication and authorization through VMODS, but it lacks native support for SSL / TLS. You can use a SSL / TLS agent such as Hitch or NGINX to enable HTTPS for Varnish Cache.

You can also use Varnish Cache as Web application firewalls, DDoS attack defenses, hot link protectors, load balancers, integration points, single sign-on gateways, authentication and authorization policy mechanisms, quick fixes for unstable backends, and HTTP request routers.

8.Squid Caching Proxy

Squid is another free, open source, outstanding and widely used proxy and caching solution for Linux. It is a feature-rich Web proxy cache server software that provides proxy and caching services for popular network protocols, including HTTP,HTTPS and FTP. It can also run on other UNIX platforms and Windows.

Just like Varnish Cache, it receives requests from the client and passes them to the specified back-end server. When the back-end server responds, it stores a copy of the content in the cache and then passes it to the client. Future requests for the same content will be processed from the cache to deliver the content to the client more quickly. Therefore, it can optimize the data flow between the client and the server to improve performance, and cache common content to reduce network traffic and save bandwidth.

Squid has functions, such as distributing load on the proxy server's hierarchy of communication with each other, generating data about Web usage patterns (for example, statistics about the most visited sites), enabling you to analyze, capture, block, replace, or modify messages that are being proxied.

It also supports security features such as rich access control, authorization and authentication, SSL / TLS support, and activity logging.

9.NGINX

NGINX (pronounced Engine-X) is an open source, high-performance, full-featured, and very popular integrated solution for setting up the Web infrastructure. It is a HTTP server, a reverse proxy server, a mail proxy server and a general TCP / UDP proxy server.

NGINX provides basic caching capabilities, where the cached content is stored in a persistent cache on disk. What's interesting about content caching in NGINX is that when it can't get fresh content from the original server, it can be configured to pass stale content from its cache.

NGINX provides a variety of security features to protect your Web system, including SSL termination, restricting access using HTTP basic authentication, authentication based on sub-request results, JWT authentication, restricted access to proxy HTTP resources, geographically restricted access, and more.

It is typically deployed as reverse proxies, load balancers, SSL finalizers / security gateways, application accelerators / content caches and API gateways in the application stack. It is also used for streaming media.

10. Apache Traffic Server

Last but not least, we have Apache Traffic Server, an open source, fast, extensible and extensible cache proxy server that supports HTTP/1.1 and HTTP/2.0. It aims to improve network efficiency and performance by caching frequently accessed content at the edge of the network for enterprises, ISP (Internet server providers), backbone network providers, and so on.

It supports forward and reverse proxies for HTTP/HTTPS communications. It can also be configured to run in one or both modes simultaneously. It has persistent cache, plug-in API; supports ICP (Internet cache protocol), ESI (including edges), Keep-Alive and so on.

In terms of security, Traffic Server supports controlling client access by allowing you to configure clients that allow proxy caching, SSL termination of connections between clients and themselves, and between themselves and the original server. It also supports authentication and basic authorization through plug-ins, logging (every request received and every error detected), and monitoring.

Traffic Server can be used as Web proxy cache, forward proxy, reverse proxy, transparent proxy, load balancer, or in cache hierarchies.

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