Failover: Difference between revisions
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{{Short description|Automatic switching from failed computer system to standby computers}} | {{Short description|Automatic switching from failed computer system to standby computers}} | ||
[[File:Duckfone.png|thumb|[[4G]] cellular failover for network resiliency]] | |||
'''Failover''' is switching to a [[redundancy (engineering)|redundant]] or standby [[computer]] [[ | '''Failover''' is switching to a [[redundancy (engineering)|redundant]] or standby [[computer]] [[server (computing)|server]], [[system]], hardware component or network upon the failure or [[abnormal end|abnormal termination]] of the previously active [[application software|application]],<ref> | ||
For application-level failover, see for example {{cite book | For application-level failover, see for example {{cite book | ||
|last= Jayaswal | |last= Jayaswal | ||
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|quote= Although it is impossible to prevent some data loss during an application failover, certain steps can [...] minimize it.}}. | |quote= Although it is impossible to prevent some data loss during an application failover, certain steps can [...] minimize it.}}. | ||
</ref> server, system, hardware component, or network in a [[computer network]]. Failover and [[switchover]] are essentially the same operation, except that failover is automatic and usually operates without warning, while switchover requires human intervention. | </ref> server, system, hardware component, or network in a [[computer network]]. Failover and [[switchover]] are essentially the same operation, except that failover is automatic and usually operates without warning, while switchover requires human intervention. | ||
[[ | == History == | ||
The term "failover", although probably in use by engineers much earlier, can be found in a 1962 declassified [[NASA]] report.<ref>[https://archive.org/details/NasaAudioHighlightReels NASA Postlaunch Memorandum Report for Mercury-Atlas], June 15, 1962.</ref> The term "switchover" can be found in the 1950s<ref>Petroleum Engineer for Management - Volume 31 - Page D-40</ref> when describing '"Hot" and "Cold" Standby Systems', with the current meaning of immediate switchover to a running system (hot) and delayed switchover to a system that needs starting (cold). A conference proceedings from 1957 describes computer systems with both Emergency Switchover (i.e. failover) and Scheduled Failover (for maintenance).<ref>[https://books.google.com/books?id=qzxNAAAAYAAJ&q=switchover Proceedings of the Western Joint Computer Conference], Macmillan 1957</ref> | |||
At the server level, failover automation usually uses a | ==Failover== | ||
[[Systems design]]ers usually provide failover capability in servers, systems or networks requiring [[high availability]] and a high degree of [[reliability engineering|reliability]]. | |||
At the server level, failover automation usually uses a [[heartbeat (computing)|heartbeat]] system that connects two servers, either through using a separate cable (for example, [[RS-232]] serial ports/cable) or a network connection. In the most common design, as long as a regular "pulse" or heartbeat continues between the main server and the second server, the second server will not bring its systems online; however a few systems actively use all servers and can failover their work to remaining servers after a failure. There may also be a third "spare parts" server that has running spare components for "hot" switching to prevent downtime. The second server takes over the work of the first as soon as it detects an alteration in the heartbeat of the first machine. Some systems have the ability to send a notification of failover. | |||
Certain systems, intentionally, do not failover entirely automatically, but require human intervention. This "automated with manual approval" configuration runs automatically once a human has approved the failover. | Certain systems, intentionally, do not failover entirely automatically, but require human intervention. This "automated with manual approval" configuration runs automatically once a human has approved the failover. | ||
==Failback== | |||
'''Failback''' is the process of restoring a system, component, or service previously in a state of failure back to its original, working state, and having the standby system go from functioning back to standby. | '''Failback''' is the process of restoring a system, component, or service previously in a state of failure back to its original, working state, and having the standby system go from functioning back to standby. | ||
The use of [[ | ==Usage== | ||
The use of [[platform virtualization|virtualization]] software has allowed failover practices to become less reliant on physical hardware through the process referred to as [[migration (virtualization)|migration]] in which a running virtual machine is moved from one physical host to another, with little or no disruption in service. | |||
Failover and failback technology are also regularly used in the Microsoft SQL Server database, in which SQL Server Failover Cluster Instance (FCI) is installed/configured on top of the Windows Server failover Cluster (WSFC). The SQL Server groups and resources running on WSFC can manually be failover to the second node<ref>https://www.dbsection.com/how-to-failover-cluster-from-one-node-to-another/</ref> for any planned maintenance on the first node or automatically failover to the second node in case of any issues on the first node. In the same way, a failback operation can be performed to the first node once the issue is resolved or maintenance is done on it. | |||
==See also== | ==See also== | ||
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* [[Computer cluster]] | * [[Computer cluster]] | ||
* [[Data integrity]] | * [[Data integrity]] | ||
* [[Fail-safe]] | |||
* [[Fault-tolerance]] | * [[Fault-tolerance]] | ||
* [[Fencing (computing)]] | * [[Fencing (computing)]] | ||
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==References== | ==References== | ||
{{Reflist | {{Reflist}} | ||
{{Authority control}} | {{Authority control}} | ||
[[Category:Computer networking]] | [[Category:Computer networking]] | ||
[[Category:Fault-tolerant computer systems]] | [[Category:Fault-tolerant computer systems]] | ||
Latest revision as of 22:30, 12 June 2025
Failover is switching to a redundant or standby computer server, system, hardware component or network upon the failure or abnormal termination of the previously active application,[1] server, system, hardware component, or network in a computer network. Failover and switchover are essentially the same operation, except that failover is automatic and usually operates without warning, while switchover requires human intervention.
History
The term "failover", although probably in use by engineers much earlier, can be found in a 1962 declassified NASA report.[2] The term "switchover" can be found in the 1950s[3] when describing '"Hot" and "Cold" Standby Systems', with the current meaning of immediate switchover to a running system (hot) and delayed switchover to a system that needs starting (cold). A conference proceedings from 1957 describes computer systems with both Emergency Switchover (i.e. failover) and Scheduled Failover (for maintenance).[4]
Failover
Systems designers usually provide failover capability in servers, systems or networks requiring high availability and a high degree of reliability.
At the server level, failover automation usually uses a heartbeat system that connects two servers, either through using a separate cable (for example, RS-232 serial ports/cable) or a network connection. In the most common design, as long as a regular "pulse" or heartbeat continues between the main server and the second server, the second server will not bring its systems online; however a few systems actively use all servers and can failover their work to remaining servers after a failure. There may also be a third "spare parts" server that has running spare components for "hot" switching to prevent downtime. The second server takes over the work of the first as soon as it detects an alteration in the heartbeat of the first machine. Some systems have the ability to send a notification of failover.
Certain systems, intentionally, do not failover entirely automatically, but require human intervention. This "automated with manual approval" configuration runs automatically once a human has approved the failover.
Failback
Failback is the process of restoring a system, component, or service previously in a state of failure back to its original, working state, and having the standby system go from functioning back to standby.
Usage
The use of virtualization software has allowed failover practices to become less reliant on physical hardware through the process referred to as migration in which a running virtual machine is moved from one physical host to another, with little or no disruption in service.
Failover and failback technology are also regularly used in the Microsoft SQL Server database, in which SQL Server Failover Cluster Instance (FCI) is installed/configured on top of the Windows Server failover Cluster (WSFC). The SQL Server groups and resources running on WSFC can manually be failover to the second node[5] for any planned maintenance on the first node or automatically failover to the second node in case of any issues on the first node. In the same way, a failback operation can be performed to the first node once the issue is resolved or maintenance is done on it.
See also
- Computer cluster
- Data integrity
- Fail-safe
- Fault-tolerance
- Fencing (computing)
- High-availability cluster
- IT disaster recovery
- Load balancing
- Log shipping
- Safety engineering
- Teleportation (virtualization)
References
- ↑ For application-level failover, see for example Script error: No such module "citation/CS1"..
- ↑ NASA Postlaunch Memorandum Report for Mercury-Atlas, June 15, 1962.
- ↑ Petroleum Engineer for Management - Volume 31 - Page D-40
- ↑ Proceedings of the Western Joint Computer Conference, Macmillan 1957
- ↑ https://www.dbsection.com/how-to-failover-cluster-from-one-node-to-another/