Saturday, October 29, 2011

How to implement High Availability?

How to implement High Availability solution?

How to implement High Availability solution for your high traffic web pages or for your mission critical application?

You can use the new server and believe that the new server will not break. That may be true, but not later rely. You can use RAID. But this will only protect against disc crashes. If you drive controller but broke down as I mentioned in a previous article so you do not force anything. Probably best to design and implement server as High Available Cluster.

There are several solutions to this issue from different companies. Of course, every company claims that its solution is best.

Generally we can say that HA solved using certified hardware, software and configuration of these systems, an experienced professional should be resistant against unforeseen outages and hardware failures.

If we need to ensure the availability of a service or misssion critical application must use at least two computers. One computer will work and one for him to oversee. In case of failure of the working computer's function assumes that oversaw a computer. When it comes to recovery of a broken computer and the computer returns to its default settings.

HA Cluster can probably easiest to realize with the help of Heartbeat daemon or service. Heartbeat allows you to connect two computers to the cluster. For each machine is defined by a set of services, which has run on it. After starting the daemon will first try to communicate with the daemon on a second computer in the cluster, if it finds that it works, starts services that are run. He regularly with a demon on the other computer diagnostic messages exchanged. If the demon finds in the course of action that the other computer did not respond to him long enough, begins to act. Verifies that the second computer is really dead, and then your computer starts up services that run on a crashed computer. Sometimes it even takes over its IP address. Accidents should be seen more than a very short outage necessary to start the service. After recovering crashed computer services will start again on the original computer.

Saturday, October 22, 2011

High availability of applications

High availability of applications

If you have a problem with the fact that failure of mission-critical applications threaten the business. If you require guaranteed availability of the application is appropriate to apply cluster solution.

Failure of a server power failure, natural disaster are a nightmare to run mission critical applications and high aveilebilyty systems. Malfunction of critical applications can directly affect the business. Every IT department backs up, but recovery is quite often a lengthy process which is necessary to ensure identical hardware, install a new operating system, application and restore data. This process can take several days in order for a mission-critical applications and systems HAM unthinkable. Therefore it is necessary to ensure the permanent operation of applications.

 For these reasons, as the most cost-effective solution appears utilizing the properties of virtual infrastructure. Virtual inrastruktura encapsulates the operating system and applications installed on it and separates it from the hardware. This is possible even for the full runtime to move virtual machines from one server to another. If a server fails, the virtual machines that were run on it are automatically started and on another production server.

The high availability of virtual server infrastructure.

The high availability of virtual server infrastructure.

The term high availability is mainly used for servers connected in the cluster, which is a grouping of multiple servers (nodes) to ensure high availability of services operated within the above mentioned cluster.
When server virtualization is a topic of high availability and clustering is very important. Since the loss due to hardware error increases the number of virtual servers on that physical host not operate. For this reason it is an integral part of the cluster virtual server infrastructure. Most important is to determine which service will be provided in the high availability.

For some Failover Clusters, the virtual machine service. It is therefore necessary to determine whether to provide high availability virtual machine, or just in the virtual server service included.

Each of these cases requires the creation and configuration of the cluster at a different level and has its pros and cons. However, always need at least two physical host hypervisor role installed.

Sunday, October 16, 2011

Web farm, cluster and other systems for mission critical applications.

Once you're dealing with very high traffic site or some mission critical or Business critical applications it may be necessary to employ multiple servers. 

There are a variety of services, which definitely should not be inaccessible. For those of you who must run services, which will run for weeks, months and years without a single failure It's good to deploy a high availability system or use a solution such as web farm clustering, load balancing, or to use virtualization or cloud computing use.

Network Load Balancing (NLB)

allows you to connect up to 32 servers. These servers have a common virtual IP address. client, which communicates with the virtual address, in fact, can actually communicate with any node. This provides continuous service availability.
In case of any of the nodes, the client communicates with other nodes. The advantage of NLB is also the possibility of decomposition of the traffic load on each node. This solution is quite cheap, even the administration.


This technology allows you to combine 2, 4, or up to 8 servers. The servers are connected to one disc data storage system. Clustered service can run on one of the nodes and only if there is any failure, so the service is started on another node, and reads the disk array data. Cluster performance will not rise, but only for high availability services. Use of certified hardware is commonplace in this case.

Cluster is not a solution for everything and if you use this technology have actually doubled everything from the electricity supply, to infrastructure services such as DNS (Domain Name System).
I have seen cases where the system broke down at the clustered disk array controller and the  expensive system was at the moment for anything.

Cloud computing  see here