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This article introduces the relevant knowledge of "what is the Elasticsearch election mechanism". In the operation process of actual cases, many people will encounter such difficulties. Next, let Xiaobian lead you to learn how to deal with these situations. I hope you can read carefully and learn something!

ES Cluster Composition

ES cluster is composed of nodes. Node types can be configured as follows:

conf/elasticsearch.yml: node.master: true/false node.data: true/false

node.master: true --candidate node for master, can participate in elections, often referred to as master-eligible node in ES documentation

node.data: true --Data node that stores data for shards assigned to the node and is responsible for writing, querying, etc. of those shards.

Any node in a cluster can execute any request, and it is responsible for forwarding the request to the corresponding node for processing, so when node.master and node.data are both false, this node can act as a proxy-like node, accepting requests and forwarding, aggregating results, etc.

node discovery

ZenDiscovery is a set of modules implemented by ES itself for node discovery and master selection, without relying on Zookeeper and other tools.

In short, node discovery depends on the following configuration:

conf/elasticsearch.yml: discovery.zen.ping.unicast.hosts: [1.1.1.1, 1.1.1.2, 1.1.1.3]

This configuration can be seen as establishing an edge from this node to each node in the hosts. When all nodes in the whole cluster form a connectivity graph, all nodes can know which nodes are in the cluster and will not form islands. This is the official recommendation for all master-eligible nodes.

Master Election

As mentioned above, there may be multiple master candidate nodes in the cluster, and in this case, master election is required to ensure that only one is elected as master. If more than one node is elected as master, the cluster will have a brain split, which will destroy the consistency of the data, resulting in uncontrollable cluster behavior and various unexpected effects.

In order to avoid brain splitting, ES adopts the common distributed system idea, ensuring that the elected master is recognized by the candidate nodes of the majority (quorum), so as to ensure that there is only one master. This quorum is configured with the following configuration:

conf/elasticsearch.yml: discovery.zen.minimum_master_nodes: 2"Elasticsearch election mechanism is what" content introduced here, thank you for reading. If you want to know more about industry-related knowledge, you can pay attention to the website. Xiaobian will output more high-quality practical articles for everyone!

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