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The most common size for an HA cluster is a two-node cluster, since that is the minimum required to provide redundancy, but many clusters consist of many more, sometimes dozens of nodes. The attached diagram is a good overview of a classic HA cluster, with the caveat that it does not make any mention of quorum/witness functionality (see above).
OpenSAF is focused on Service Availability beyond High Availability (HA) requirements. While little formal research is published to improve high availability and fault tolerance techniques for containers and cloud, [5] research groups are actively exploring these challenges with OpenSAF.
Container clusters need to be managed. This includes functionality to create a cluster, to upgrade the software or repair it, balance the load between existing instances, scale by starting or stopping instances to adapt to the number of users, to log activities and monitor produced logs or the application itself by querying sensors.
The failure of disk hardware or a given storage node in a cluster can create a single point of failure that can result in data loss or unavailability. Fault tolerance and high availability can be provided through data replication of one sort or another, so that data remains intact and available despite the failure of any single piece of equipment.
The Linux-HA (High-Availability Linux) project provides a high-availability solution for Linux, FreeBSD, OpenBSD, Solaris and Mac OS X which promotes reliability, availability, and serviceability (RAS). [1] The project's main software product is Heartbeat, a GPL-licensed portable cluster management program for high-availability clustering. Its ...
The basic architecture of VCS includes low-latency transport (LLT), the Global Membership Services and Atomic Broadcast Protocol (GAB), the High Availability Daemon (HAD), and Cluster Agents. LLT lies at the bottom of the architecture and acts as conduit between GAB and underlying network.
DRBD layers logical block devices (conventionally named /dev/drbdX, where X is the device minor number) over existing local block devices on participating cluster nodes. Writes to the primary node are transferred to the lower-level block device and simultaneously propagated to the secondary node(s). The secondary node(s) then transfers data to ...
The tradeoff between availability, consistency and latency, as described by the PACELC theorem. In database theory, the PACELC theorem is an extension to the CAP theorem.It states that in case of network partitioning (P) in a distributed computer system, one has to choose between availability (A) and consistency (C) (as per the CAP theorem), but else (E), even when the system is running ...