How to make an Appilcation that supports ZERO DOWN TIME ?

Question

I just want to know what are all the techniques or technologies available to make sure that our applications downt time is ZERO.

I mean system should not go down while upgrading, deployment, or any database changes.

Last year I think Google was down for around 2 hours due to some power failures on data centers, that impacts the Internet by 5%.

Manikavelu Velayutham · Answer

How to make the system available when we do any deployment or any database changes ? Consider a situation a user doing some transactions through an application at the sametime some fixes and enhancements are deployed to that application server. In this case how to maintain the application available when the fixes and enhancements will get reflected ? What happened to the data that were on the cache when the changes reflected in that application ?

Sam Hobbs · Answer

Are you only asking about applications? What about databases? A major part of keeping an application up is a database system that is designed to ensure that data is not lost. So a major part of the answer is to use a database system such as SQL Server that has features that support reliability and ensuring that those features are used effectively. A good database system such as SQL Server will write out all transactions immediately in real-time and in a manner that ensures data is not lost. Use of mirroring of hard drives I think is a necessity where data is written to two hard drives at the same time instead of just one. In the past transactions were written to tape. There must also be frequent backups and the backups must be coordinated with the transaction log so that the transactions that have occured after the backup (and only those transactions) can be processesd to re-create a lost database when something disastrous happens. Highly critical systems might send transactions over a network for backup purposes. Computers must have Uninteruptible Power Sources (UPSs) including a secondary power source such as a generator. A primnary UPS usually uses batteries. The UPS needs to have a monitor that sends a signal to the computer when primary power is lost so the system can do a graceful shutdown when possible. The system needs to have an application monitor software (a Windows service) that can re-start applications when needed and as needed and that can send alerts to people as needed.