A Heartbeat (Engl. For "Heartbeat" ) is a network connection between two (or more) computers in a cluster to notify each other about the fact that they are operational and their tasks can meet yet, so are "alive". In the environment of network protocols such as B. HSRP or OSPF , " keepalive " and "hello" messages describe this function.
If there are no notifications from another computer, a program on the “surviving” computer assumes that this partner counterpart is no longer available (e.g. due to a defect or a program error ) and that it should ensure that it is Tasks are taken over by a still functioning computer.
It takes place on the network access layer , usually via null modem cable , Ethernet or Fiber Channel .
Outside of cluster technology, the term was also used for a function used for error analysis in Ethernet cabling via Yellowcable (10 Mbit / s ). The heartbeat could be switched on or off for each transceiver .
Split brain is a situation when the heartbeat connection between the computers (e.g. via Ethernet or serial interface ) is interrupted and does not come back within the required time. Although the computers each work perfectly, the control programs on these computers must assume that the other has failed.
After that, no node knows which role it should currently play and automatically makes itself the primary node. With active / passive configurations, this leads to the failure of the cluster and the services offered and, when using a shared data storage device ( storage backends such as DRBD ), can result in both systems trying to write to the same storage device at the same time.
If two or more computers require the same resource to perform a task, for example a network address, MAC address or a file system , it may be necessary to ensure that this resource is never used by more than one computer at the same time. In the English-language literature, the term node fencing is used for this , which means something like computer fences .
STONITH is one possibility of this exclusion. If both computers are connected to a STONITH device (usually via a serial interface), one computer can switch off the opposite computer in a split-brain situation. There are two ways to use the STONITH principle: on the application or hardware level. The latter has the advantage that it does not depend on software ( e.g. an SSH daemon). To minimize the impact of hardware failures, heartbeat networks are often set up with redundant switches and each system involved is connected with two or more network cards.
The naming of the hitherto most massive security gap on the Internet was based on a play on words. Since this security gap, which affected two thirds of all websites worldwide at the beginning of 2014, leads to an outflow - in other words, bleeding out - of vital user data during the heartbeat functionality, the term heartbleed bug became established .
- ↑ Federal Office for Information Security: BSIFB - Information - Information on the security gap "Heartb ... January 13, 2016. Archived from the original on January 13, 2016.
- Control program "Heartbeat" of the "High Availability Linux" project (English)
- MyWindowsHeartbeat , Open Source Heartbeat for Windows (English)
- Cluster Resource Manager The resource management program outsourced from the "High Availability Linux" project in 2007