• This section contains modules responsible for various aspects of the functionality in Elasticsearch. Each module has settings which may be:

• Cluster level settings decide the allocation of shards to different nodes and reallocation of shards to rebalance cluster. These are the following settings to control shard allocation −

• This module helps a cluster to discover and maintain the state of all the nodes in it. The state of cluster changes when a node is added or deleted from a cluster. The cluster name setting is used to create logical difference between different clusters. There are some modules which help you to use the APIs provided by cloud vendors and those are −

• Azure discovery
• EC2 discovery
• Google compute engine discovery
• Zen discovery

• This module maintains the cluster state and the shard data across full cluster restarts. Following are the static settings of this module −

Setting	Possible value	Description
gateway.expected_ nodes	numeric value (by default 0)	The number of nodes that are expected to be in the cluster for the recovery of local shards.
gateway.expected_ master_nodes	numeric value (by default 0)	The number of master nodes that are expected to be in the cluster before start recovery.
gateway.expected_ data_nodes	numeric value (by default 0)	The number of data nodes expected in the cluster before start recovery.
gateway.recover_ after_time	String value (by default 5m)	This specifies the time for which the recovery process will wait to start regardless of the number of nodes joined in the cluster. gateway.recover_ after_nodes gateway.recover_after_ master_nodes gateway.recover_after_ data_nodes

• This module manages the communication between HTTP client and Elasticsearch APIs.
• This module can be disabled by changing the value of http.enabled to false. The following are the settings (configured in elasticsearch.yml) to control this module −

Sr.No	Setting & Description
1	http.port This is a port to access Elasticsearch and it ranges from 9200-9300.
2	http.publish_port This port is for http clients and is also useful in case of firewall.
3	http.bind_host This is a host address for http service.
4	http.publish_host This is a host address for http client.
5	http.max_content_length This is the maximum size of content in an http request. Its default value is 100mb.
6	http.max_initial_line_length This is the maximum size of URL and its default value is 4kb.
7	http.max_header_size This is the maximum http header size and its default value is 8kb.
8	http.compression This enables or disables support for compression and its default value is false.
9	http.pipelinig This enables or disables HTTP pipelining.
10	http.pipelining.max_events This restricts the number of events to be queued before closing an HTTP request.

• This module maintains the settings, which are set globally for every index. The following settings are mainly related to memory usage −

• This is used for preventing operation from causing an OutOfMemroyError.
• The setting mainly restricts the JVM heap size.
• For example, indices.breaker.total.limit setting, which defaults to 70% of JVM heap.

• This is used mainly when aggregating on a field.
• It is recommended to have enough memory to allocate it.
• The amount of memory used for the field data cache can be controlled using indices.fielddata.cache.size setting.

• This memory is used for caching the query results.
• This cache uses Least Recently Used (LRU) eviction policy. Indices.queries.cahce.size setting controls the memory size of this cache.

• This buffer stores the newly created documents in the index and flushes them when the buffer is full.
• Setting like indices.memory.index_buffer_size control the amount of heap allocated for this buffer.

• This cache is used to store local search data for every shard.
• Cache can be enabled during the creation of index or can be disabled by sending URL parameter.

• It controls the resources during recovery process. The following are the settings −

Setting	Default value
indices.recovery.concurrent_streams	3
indices.recovery.concurrent_small_file_streams	2
indices.recovery.file_chunk_size	512kb
indices.recovery.translog_ops	1000
indices.recovery.translog_size	512kb
indices.recovery.compress	true
indices.recovery.max_bytes_per_sec	40mb

• Time to Live (TTL) interval defines the time of a document, after which the document gets deleted. The following are the dynamic settings for controlling this process −

Setting	Default value
indices.ttl.interval	60s
indices.ttl.bulk_size	1000

Node

• Each node has an option to be data node or not.
• You can change this property by changing node.data setting.
• Setting the value as false defines that the node is not a data node.

The modules in this section are:

Cluster-level routing and shard allocation

Settings to control where, when, and how shards are allocated to nodes.

Discovery

How nodes discover each other to form a cluster.

Gateway

How many nodes need to join the cluster before recovery can start.

HTTP

Settings to control the HTTP REST interface.

Indices

Global index-related settings.

Network

Controls default network settings.

Node client

A Java node client joins the cluster, but doesn’t hold data or act as a master node.

Painless

A built-in scripting language for Elasticsearch that’s designed to be as secure as possible.

Plugins

Using plugins to extend Elasticsearch.

Scripting

Custom scripting available in Lucene Expressions, Groovy, Python, and Javascript. You can also write scripts in the built-in scripting language, Painless.

Snapshot/Restore

Backup your data with snapshot/restore.

Thread pools

Information about the dedicated thread pools used in Elasticsearch.

Transport

Configure the transport networking layer, used internally by Elasticsearch to communicate between nodes.

Tribe nodes

A tribe node joins one or more clusters and acts as a federated client across them.

Cross cluster Search

Cross cluster search enables executing search requests across more than one cluster without joining them and acts as a federated client across them.