Website monitoring is the process of testing or tracking (monitoring) how end-users interact with a website or web application.

Website monitoring is often used by businesses to ensure that their customers are able to access their online

applications and perform actions such as searching, online shopping, checking an account balance, or simply researching.

Monitoring is essential to ensure that a website is available to users and downtime is minimized.

Users that rely on a website or an application for work or pleasure will get frustrated or even stop using the application if it is not reliably available.

Monitoring can cover many things that an application needs to function, like network connectivity, Domain Name System records, database connectivity, bandwidth, and computer resources like free RAM, CPU load, disk space, events, etc. Commonly measured metrics are response time and availability (or uptime), but consistency and reliability metrics are gaining popularity.

Website monitoring can be done from both inside and outside of a corporate firewall.

Traditional Network Management solutions focus on inside the firewall monitoring, whereas external performance monitoring will test and monitor performance issues across the Internet backbone and in some cases all the way to the end-user.

External performance monitoring is also known as end-user monitoring or end-to-end performance monitoring.

Real user monitoring measures the performance and availability experienced by actual users, diagnoses individual incidents, and tracks the impact of a change..

Website monitoring service can check HTTP pages, HTTPS, FTP, SMTP, POP3, IMAP, DNS, SSH, Telnet, SSL, TCP, PING, Domain Name Expiry, SSL Certificate Expiry and a range of other ports with great variety of check intervals from every 4 hours to every one minute. Typically, most website monitoring services test your server anywhere between once-per hour to once-per-minute.

Time performances: for example an HTTP page should answer in less than 1 second (for a download of 16Ko) to be considered as "good".

You may monitor a single page of your website, but you can also monitor a complete business process (often referred to as multi-step transactions).

Website monitoring services usually have a number of servers around the globe - USA, Europe, Asia, Australia and other locations. By having multiple servers in different geographic locations, monitoring service can determine if a Web server is available across different Networks worldwide. Some vendors claim that the more locations the better picture on your website availability while others say that three globally distributed stations are sufficient and more stations do not give more information.

There are two main types of website monitoring:

Synthetic monitoring also known as active monitoring, and Passive monitoring also known as real monitoring.

Synthetic monitoring (also known as active monitoring) is website monitoring that is done using a web browser emulation or scripted real web browsers. Behavioral scripts (or paths) are created to simulate an action or path that a customer or end-user would take on a site. Those paths are then continuously monitored at specified intervals for availability and response time measures.

Synthetic monitoring is valuable because it enables a webmaster to identify problems and determine if his website or web application is slow or experiencing downtime before that problem affects actual end-users or customers. This type of monitoring does not require actual web traffic so it enables companies to test web applications 24x7, or test new applications prior to a live customer-facing launch.

Because synthetic monitoring is a simulation of typical user behavior or navigation through a website, it is often best used to monitor commonly trafficked paths and critical business processes. Synthetic tests must be scripted in advance, so it is not feasible to measure performance for every permutation of a navigational path an end-user might take. This is more suited for passive monitoring. Synthetic testing is useful for measuring availability and response time of critical pages and transaction (how a site performs from all geographies) but doesn't monitor or capture actual end-user interactions.

Passive monitoring is a technique used to capture traffic from a network by generating a copy of that traffic, often from a span port or mirror port or via a network tap. Once the data (a stream of frames or packets) has been extracted, it can be used in many ways.

It can be analyzed in a sniffer such as Wireshark

It can be examined for flows of traffic, providing information on "top talkers" in a network as well as TCP round-trip time.

It can be reassembled according to an application's state machine into end-user activity (for example, into database queries, e-mail messages, and so on.) This kind of technology is common in Real User Monitoring when applied to the http protocol in web applications. In some cases, http reassembly is further analyzed for web analytics

Passive monitoring can be very helpful in troubleshooting performance problems once they have occurred. Passive monitoring differs from synthetic monitoring in that it relies on actual inbound web traffic to take measurements, so problems can only be discovered after they have occurred.

While initially viewed as competitive to synthetic monitoring approaches, most networking professionals now recognize that passive and synthetic monitoring are complementary.

As the information brought by website monitoring services is in most cases urgent and may be of crucial importance, various notification methods, often known as "alerts" are used: e-mail, IM, regular and cell phones, SMS, fax, pagers, Skype, etc.

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