VMware HA : ‘V’irtually ‘M’ore - High Availability
Today i want to discuss something about High Availability feature of VMware. First of all….what is high availability? why we need to concentrate on this thing? how can we accomplish this thing with the help of vmware? Come, Let’s support…. by providing High Availability in the environment where you are working on….
What is High Availability ?
High Availability is nothing but, the continuity of the service. That means the service should be available to the users 24x7 without any interruption.
Why we need to concentrate on this thing?
Now a days every business / company / organization is integrated with internet marketing. By depending on internet marketing these guys are making more money. Which means internet became a medium to the user / customer and the company / business. So a company can make money from all over the world with out having their offices / stores located in each locality. Instead of these they are putting their servers in each location, because these are the guys who are providing services to the users / customers.
If the user faces any interruption in the service, that means the company is losing its business. To avoid such things each and every company concentrating on providing high availability for their environments in the means of Clustering, Redundancy at all levels (Software and Hardware) and Load Balancing etc. For that reason as a systems engineer we need to concentrate on these things too….
How can we accomplish this High Availability in our environments?
There are lot of technologies available today to provide HA to the environment. Major thing is we need to know about those technologies. For example Clustering, Grid Computing, Load Balancing, Hardware Redundancy, Software redundancy, DR Sites and Finally VMware HA…. :)
How can we accomplish this High Availability with VMware HA?
After eating lot of your time, i am coming to the point now. i have discussed these things because there are lot of people who wants to come into this industry with lot of ambition, but without ignition. I want to support them, by igniting their knowledge… Finally lets talk about vmware HA.
As usual it is also a very good feature from VMware. With this we can provide High Availability to the virtual machines which are running in/on ESX cluster. We have lot of features like VMotion, DRS, SMP etc, but why we need this one. We need this because we need our services running without interruption. Assume like, for some reason if any one of the ESX server in the cluster goes down suddenly, what happens to the virtual machines which are running on that particular server? Are they continue to run or go down. Yes, they also goes down. But with the help of VMware HA, these vm’s can be restarted immediately on the other ESX servers in the same cluster. But here you will get a down time of 5 –10 mins. Because server crash is an unexpected thing.
How it works?
When you add a ESX server to the HA enabled cluster in the VC, what happens is VC installs an agent called HA agent on each ESX server. Using this HA agent, all the servers are knowing about each other by sending heartbeat packets saying that “I am ALIVE”. For every 5 seconds, each and every server in the cluster will send this packet to all other servers. So that every server knows about the other. If for some reason like, server crash or server hang or if the server is in maintenance mode this packet will never be sent by the server. At that moment, each and every live server in the cluster will be aware of the dead server. Immediately HA agents calculate the resources, and try to restart the vm’s on all the running servers.
Note : HA feature is not dependent on VC or VMotion.
If the host gets disconnected from the VC, at that moment also the HA agent will be running on the host. But the only thing is the resources data of that host will not be updated in the database. Because VC is using SQL/Oracle database to store the vm, resource, host, cluster, datacenter & what not ever information.
And remember, in restarting the VM’s HA is never be using VMotion.
……………. Thats all for now, i will discuss more in the next article.
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