Availability
Availability Availability of a site shows if a site is accessible from the Internet.

Availability of a site shows if a site is accessible from the Internet. This term is also about access to a server, database or another entity. As all objects in the Internet are based on comlicated infrastructure, nothing can be available always. The question is how to measure it, what is normal and if we may affect it anyway. The measurement of availability is connected to terms Uptime and Downtime, which show for how long a site is unavailable. However, these values can not create the full view of the situation. There could be many reasons of unavailability - server or connection problems, application error, overload of the site and so on. To avoid or shorter the failures, it is needed to supervise the site and analyze the errors, if they happen. For these purposes there are special monitoring tools, which help to increase to availability of the site, collect statistics and provide necessary information about the errors for fast repair. These tools are called Website Monitoring services.

  • CM.Glossary.WebsiteMonitoring
  • CM.Glossary.Downtime
  • CM.Glossary.Uptime
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Snapshot - instrument for site supervision

How does the site look like when I’m not looking at it? What if it looks bad or does not work at all? HostTracker offers an instrument for site supervision - snapshot feature. Let’s take a look at its practical application.

How does the site look like when I’m not looking at it? What if it looks bad or does not work at all? HostTracker offers an instrument for site supervision - snapshot feature. Let’s take a look at its practical application.

What’s going on with my site?

Now it’s usual to use different services and applications for site maintenance and support, and sometimes they do report some problems. Often we feel the lack of information - Google Analytics or a similar service reports the downtime and renewal, but likely we will never know what exactly has happened. To investigate the issue, it is necessary to review the logs, write to hosting support and perform many others exhausting actions, frequently - with no result. There are also more interesting cases - when a site is not available from a certain country or is not downloaded completely. Such problems could long for months, or even years, till they are accidentally detected. One more important issue - content check. It will automatically review the content of the site and inform the responsible staff in case it has disappeared - for example, something has not been able to be downloaded from the database. But it’s hard to find the cause if the issue is short-term, because people usually do not sit in front of a laptop refreshing the page every minute. To resolve the problem, HostTracker offers a new feature - snapshot. It is very simple in use and does not require any additional adjustments. The service simply makes a snapshot of the checked page every time and saves it for review in two ways: page source code and html-view. This let you easily see how the page looks at the moment of failure, understand what’s wrong and fix the problem quickly without spending time for diagnostics. It saves lots of time for server administrator, developers and other concerned people.

How does it work

Doing the regular checks, our servers with predefined interval try to download the checked page. Additional algorithms could be used at the moment - the page could be parsed for keywords to make sure that this is the one we are looking for (there are cases when an error page returns 200, Ok, http code, or when redirection is activated in case of error). If there is no error - fine. But if there is, it will be written down into the HostTracker log, which is easily available from the web. Then, notification are sent and a snapshot is made.

The snapshots could also be found in the log - if several errors were detected, a different snapshot will be available from each one.


Though there are some remarks. First, we do not run javascript while making snapshot - same thing for regular check. Second, the error must be detectable. It means, the server must return something. In case of timeout or connection error - snapshot will not help, and only a corresponding record will remain in the log.

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Home > Blog > HostTracker_under_Azure

Those, who actively involved with the Web, should know HostTracker, a company from Ukraine, which has been supporting one of the leading global web monitoring services since 2004. Its goal is to monitor site health and accessibility in near-real-time access. Using alert message system, HostTracker allows to reduce downtimes, to improve quality of service for users, to quickly localize troubles...

​Those, who actively involved with the Web, should know HostTracker, a company from Ukraine, which has been supporting one of the leading global web monitoring services since 2004. Its goal is to monitor site health and accessibility in near-real-time access. Using alert message system, HostTracker allows to reduce downtimes, to improve quality of service for users, to quickly localize troubles, and etc.

Architecturally, HostTracker includes a server-based hub, acting both as a data collector and control center, and a series of software agents, launched in various regions – typically using the equipment operated by major providers, hosters and affiliates. The geographically distributed architecture provides common system reliability and also allows collecting data in terms of access speed, bandwidth and other key performance characteristics on regional level – a critically important feature for the international business.

The first version of HostTracker, which is still functioning and providing services for tens of thousands of customers, was Linux based. Today, it is supported by nine control servers, located and organized in two DPCs on collocation principle, and few dozens of agents. Considering that the final objective of web monitoring is focused on increasing the uptime of client-based web resources – whereas 95% of HostTracker customers were able to increase it up to 99% – then, performance and accessibility of the service itself are not just critical, but rather fundamental parameters that influence the whole business. Theoretically, HostTracker should demonstrate accessibility close to 100%. However, an extensive growth of the service made this task hard to solve.

HostTracker was facing constantly increasing network traffic – a problem for seamless operation of the service. Inability to add new control servers on-the-fly, difficulties when maintaining not uniform and multiple-aged hardware was another limiting factor. Moreover, the desire to develop the service through wider protocol and network service support was meeting certain obstacles. “Unfortunately, for Linux there was a limited choice of ready-to-use solutions and libraries, while inventing something completely new was difficult”, says Artem Prisyazhnyuk, HostTracker director. “We had an idea of reviewing the stack of technologies we used for a more sophisticated one and after taking a closer look at the .NET platform, its potential in terms of scalability and network support, I realized that was exactly the thing we had been looking for.”

It was sure that migrating to a completely different platform should be a complex task – the project extended over three years. However, it was like blessing in disguise: during this period, the world has seen the cloud computing that seemed an ideal tool for solving both the scalability problem and putting aside one’s own whole infrastructure. Besides, the PaaS model allowed to remove most of the effort in terms of administering the solution and to control the application as a self-contained entity, to the extent of complete automation, and thus, Windows Azure had in fact no alternatives.

As a result, the second version of HostTracker, commercial operation of which started in May 2012, is already functioning under Windows Azure. Its central ingredient is realized as Web Role and associated with SQL Azure Database – it provides external portal, analytics and report generation, control of monitoring applications. The latter are ensured with instances of Worker Role, which also use SQL Azure Database to store their data and to provide the service scalability depending on the network loading. Agents are functioning as they did before, with the viability of their transfer to Windows Azure being considered.
Now, HostTracker uses HTTP/HTTPS and ICMP protocols to monitor specific ports, including various methods (HEAD/POST/GET), and etc.
 

HostTracker instant check



Alarm reporting is available via email, SMS and instant messages. The customer can receive reports with statistics about resources being controlled and their performances. You can spend only 6 minutes to make monitoring settings for five sites, while the average response time in case of failure is limited by a couple of minutes, and it takes 1-3 minutes more to inform the customer about the problem. Using this service, anyone can check any site, including access from various regions.

 As a result, if on the one side the transfer to the .NET platform itself gave us the potential to modernize HostTracker, to optimize the application architecture and realize new internal functions, then, on the other side, the migration to the cloud allowed to refuse from less important, though time consuming activities such as administering the solution, and, first of all, to reach necessary performance indicators. Microsoft, for all basic Windows Azure services, declares 99,9% accessibility and guarantees monthly refunds, should this indicator be lower. This creates a firm ground for operating such services like HostTracker, as the accessibility is the most critical parameter for these applications. Using the cloud infrastructure also provides a better protection for the service: unauthorized access to the application and many types of attacks are effectively excluded, while the data safety is ensured by triple reservation.

HostTracker received another advantage from abandoning its own infrastructure. The service’s performance characteristics are also rather critical, for they directly affect the failure reporting system operation. In this respect, Windows Azure is virtually a drainless source of computing power. This means that by timely starting additional monitoring instances you can support HostTracker functioning parameters on the necessary level. Moreover, the cloud environment is exactly what you need in order to make this process almost fully automatic, excluding further need for direct control.

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