[[modules-node]] == Node Any time that you start an instance of Elasticsearch, you are starting a _node_. A collection of connected nodes is called a <>. If you are running a single node of {es}, then you have a cluster of one node. Every node in the cluster can handle <> and <> traffic by default. The transport layer is used exclusively for communication between nodes; the HTTP layer is used by REST clients. All nodes know about all the other nodes in the cluster and can forward client requests to the appropriate node. By default, a node is all of the following types: master-eligible, data, ingest, and (if available) machine learning and transform. TIP: As the cluster grows and in particular if you have large {ml} jobs or {ctransforms}, consider separating dedicated master-eligible nodes from dedicated data nodes, {ml} nodes, and {transform} nodes. <>:: A node that has `node.master` set to `true` (default), which makes it eligible to be <>, which controls the cluster. <>:: A node that has `node.data` set to `true` (default). Data nodes hold data and perform data related operations such as CRUD, search, and aggregations. <>:: A node that has `node.ingest` set to `true` (default). Ingest nodes are able to apply an <> to a document in order to transform and enrich the document before indexing. With a heavy ingest load, it makes sense to use dedicated ingest nodes and to mark the master and data nodes as `node.ingest: false`. <>:: A node that has `xpack.ml.enabled` and `node.ml` set to `true`, which is the default behavior in the {es} {default-dist}. If you want to use {ml-features}, there must be at least one {ml} node in your cluster. For more information about {ml-features}, see {ml-docs}/index.html[Machine learning in the {stack}]. + IMPORTANT: If you use the {oss-dist}, do not set `node.ml`. Otherwise, the node fails to start. <>:: A node that has `node.transform` set to `true`. If you want to use {transforms}, there must be at least one {transform} node in your cluster. For more information, see <> and <>. [NOTE] [[coordinating-node]] .Coordinating node =============================================== Requests like search requests or bulk-indexing requests may involve data held on different data nodes. A search request, for example, is executed in two phases which are coordinated by the node which receives the client request -- the _coordinating node_. In the _scatter_ phase, the coordinating node forwards the request to the data nodes which hold the data. Each data node executes the request locally and returns its results to the coordinating node. In the _gather_ phase, the coordinating node reduces each data node's results into a single global resultset. Every node is implicitly a coordinating node. This means that a node that has all three `node.master`, `node.data` and `node.ingest` set to `false` will only act as a coordinating node, which cannot be disabled. As a result, such a node needs to have enough memory and CPU in order to deal with the gather phase. =============================================== [float] [[master-node]] === Master-eligible node The master node is responsible for lightweight cluster-wide actions such as creating or deleting an index, tracking which nodes are part of the cluster, and deciding which shards to allocate to which nodes. It is important for cluster health to have a stable master node. Any master-eligible node that is not a <> may be elected to become the master node by the <>. IMPORTANT: Master nodes must have access to the `data/` directory (just like `data` nodes) as this is where the cluster state is persisted between node restarts. [float] [[dedicated-master-node]] ==== Dedicated master-eligible node It is important for the health of the cluster that the elected master node has the resources it needs to fulfill its responsibilities. If the elected master node is overloaded with other tasks then the cluster may not operate well. In particular, indexing and searching your data can be very resource-intensive, so in large or high-throughput clusters it is a good idea to avoid using the master-eligible nodes for tasks such as indexing and searching. You can do this by configuring three of your nodes to be dedicated master-eligible nodes. Dedicated master-eligible nodes only have the `master` role, allowing them to focus on managing the cluster. While master nodes can also behave as <> and route search and indexing requests from clients to data nodes, it is better _not_ to use dedicated master nodes for this purpose. To create a dedicated master-eligible node in the {default-dist}, set: [source,yaml] ------------------- node.master: true <1> node.voting_only: false <2> node.data: false <3> node.ingest: false <4> node.ml: false <5> xpack.ml.enabled: true <6> node.transform: false <7> node.remote_client_client: false <8> ------------------- <1> The `node.master` role is enabled by default. <2> The `node.voting_only` role is disabled by default. <3> Disable the `node.data` role (enabled by default). <4> Disable the `node.ingest` role (enabled by default). <5> Disable the `node.ml` role (enabled by default). <6> The `xpack.ml.enabled` setting is enabled by default. <7> Disable the `node.transform` role. <8> Disable remote cluster connections (enabled by default). To create a dedicated master-eligible node in the {oss-dist}, set: [source,yaml] ------------------- node.master: true <1> node.data: false <2> node.ingest: false <3> node.remote_cluster_client: false <4> ------------------- <1> The `node.master` role is enabled by default. <2> Disable the `node.data` role (enabled by default). <3> Disable the `node.ingest` role (enabled by default). <4> Disable remote cluster connections (enabled by default). [float] [[voting-only-node]] ==== Voting-only master-eligible node A voting-only master-eligible node is a node that participates in <> but which will not act as the cluster's elected master node. In particular, a voting-only node can serve as a tiebreaker in elections. It may seem confusing to use the term "master-eligible" to describe a voting-only node since such a node is not actually eligible to become the master at all. This terminology is an unfortunate consequence of history: master-eligible nodes are those nodes that participate in elections and perform certain tasks during cluster state publications, and voting-only nodes have the same responsibilities even if they can never become the elected master. To configure a master-eligible node as a voting-only node, set the following setting: [source,yaml] ------------------- node.voting_only: true <1> ------------------- <1> The default for `node.voting_only` is `false`. IMPORTANT: The `voting_only` role requires the {default-dist} of {es} and is not supported in the {oss-dist}. If you use the {oss-dist} and set `node.voting_only` then the node will fail to start. Also note that only master-eligible nodes can be marked as voting-only. High availability (HA) clusters require at least three master-eligible nodes, at least two of which are not voting-only nodes. Such a cluster will be able to elect a master node even if one of the nodes fails. Since voting-only nodes never act as the cluster's elected master, they may require require less heap and a less powerful CPU than the true master nodes. However all master-eligible nodes, including voting-only nodes, require reasonably fast persistent storage and a reliable and low-latency network connection to the rest of the cluster, since they are on the critical path for <>. Voting-only master-eligible nodes may also fill other roles in your cluster. For instance, a node may be both a data node and a voting-only master-eligible node. A _dedicated_ voting-only master-eligible nodes is a voting-only master-eligible node that fills no other roles in the cluster. To create a dedicated voting-only master-eligible node in the {default-dist}, set: [source,yaml] ------------------- node.master: true <1> node.voting_only: true <2> node.data: false <3> node.ingest: false <4> node.ml: false <5> xpack.ml.enabled: true <6> node.transform: false <7> node.remote_cluster_client: false <8> ------------------- <1> The `node.master` role is enabled by default. <2> Enable the `node.voting_only` role (disabled by default). <3> Disable the `node.data` role (enabled by default). <4> Disable the `node.ingest` role (enabled by default). <5> Disable the `node.ml` role (enabled by default). <6> The `xpack.ml.enabled` setting is enabled by default. <7> Disable the `node.transform` role. <8> Disable remote cluster connections (enabled by default). [float] [[data-node]] === Data node Data nodes hold the shards that contain the documents you have indexed. Data nodes handle data related operations like CRUD, search, and aggregations. These operations are I/O-, memory-, and CPU-intensive. It is important to monitor these resources and to add more data nodes if they are overloaded. The main benefit of having dedicated data nodes is the separation of the master and data roles. To create a dedicated data node in the {default-dist}, set: [source,yaml] ------------------- node.master: false <1> node.voting_only: false <2> node.data: true <3> node.ingest: false <4> node.ml: false <5> node.transform: false <6> node.remote_cluster_client: false <7> ------------------- <1> Disable the `node.master` role (enabled by default). <2> The `node.voting_only` role is disabled by default. <3> The `node.data` role is enabled by default. <4> Disable the `node.ingest` role (enabled by default). <5> Disable the `node.ml` role (enabled by default). <6> Disable the `node.transform` role. <7> Disable remote cluster connections (enabled by default). To create a dedicated data node in the {oss-dist}, set: [source,yaml] ------------------- node.master: false <1> node.data: true <2> node.ingest: false <3> node.remote_cluster_client: false <4> ------------------- <1> Disable the `node.master` role (enabled by default). <2> The `node.data` role is enabled by default. <3> Disable the `node.ingest` role (enabled by default). <4> Disable remote cluster connections (enabled by default). [float] [[node-ingest-node]] === Ingest node Ingest nodes can execute pre-processing pipelines, composed of one or more ingest processors. Depending on the type of operations performed by the ingest processors and the required resources, it may make sense to have dedicated ingest nodes, that will only perform this specific task. To create a dedicated ingest node in the {default-dist}, set: [source,yaml] ------------------- node.master: false <1> node.voting_only: false <2> node.data: false <3> node.ingest: true <4> node.ml: false <5> node.transform: false <6> node.remote_cluster_client: false <7> ------------------- <1> Disable the `node.master` role (enabled by default). <2> The `node.voting_only` role is disabled by default. <3> Disable the `node.data` role (enabled by default). <4> The `node.ingest` role is enabled by default. <5> Disable the `node.ml` role (enabled by default). <6> Disable the `node.transform` role. <7> Disable remote cluster connections (enabled by default). To create a dedicated ingest node in the {oss-dist}, set: [source,yaml] ------------------- node.master: false <1> node.data: false <2> node.ingest: true <3> node.remote_cluster_client: false <4> ------------------- <1> Disable the `node.master` role (enabled by default). <2> Disable the `node.data` role (enabled by default). <3> The `node.ingest` role is enabled by default. <4> Disable remote cluster connections (enabled by default). [float] [[coordinating-only-node]] === Coordinating only node If you take away the ability to be able to handle master duties, to hold data, and pre-process documents, then you are left with a _coordinating_ node that can only route requests, handle the search reduce phase, and distribute bulk indexing. Essentially, coordinating only nodes behave as smart load balancers. Coordinating only nodes can benefit large clusters by offloading the coordinating node role from data and master-eligible nodes. They join the cluster and receive the full <>, like every other node, and they use the cluster state to route requests directly to the appropriate place(s). WARNING: Adding too many coordinating only nodes to a cluster can increase the burden on the entire cluster because the elected master node must await acknowledgement of cluster state updates from every node! The benefit of coordinating only nodes should not be overstated -- data nodes can happily serve the same purpose. To create a dedicated coordinating node in the {default-dist}, set: [source,yaml] ------------------- node.master: false <1> node.voting_only: false <2> node.data: false <3> node.ingest: false <4> node.ml: false <5> xpack.ml.enabled: true <6> node.transform: false <7> node.remote_cluster_client: false <8> ------------------- <1> Disable the `node.master` role (enabled by default). <2> The `node.voting_only` role is disabled by default. <3> Disable the `node.data` role (enabled by default). <4> Disable the `node.ingest` role (enabled by default). <5> Disable the `node.ml` role (enabled by default). <6> The `xpack.ml.enabled` setting is enabled by default. <7> Disable the `node.transform` role. <8> Disable remote cluster connections (enabled by default). To create a dedicated coordinating node in the {oss-dist}, set: [source,yaml] ------------------- node.master: false <1> node.data: false <2> node.ingest: false <3> node.remote_cluster_client: false <4> ------------------- <1> Disable the `node.master` role (enabled by default). <2> Disable the `node.data` role (enabled by default). <3> Disable the `node.ingest` role (enabled by default). <4> Disable remote cluster connections (enabled by default). [float] [[ml-node]] === [xpack]#Machine learning node# The {ml-features} provide {ml} nodes, which run jobs and handle {ml} API requests. If `xpack.ml.enabled` is set to `true` and `node.ml` is set to `false`, the node can service API requests but it cannot run jobs. If you want to use {ml-features} in your cluster, you must enable {ml} (set `xpack.ml.enabled` to `true`) on all master-eligible nodes. If you want to use {ml-features} in clients (including {kib}), it must also be enabled on all coordinating nodes. If you have the {oss-dist}, do not use these settings. For more information about these settings, see <>. To create a dedicated {ml} node in the {default-dist}, set: [source,yaml] ------------------- node.master: false <1> node.voting_only: false <2> node.data: false <3> node.ingest: false <4> node.ml: true <5> xpack.ml.enabled: true <6> node.transform: false <7> node.remote_cluster_client: false <8> ------------------- <1> Disable the `node.master` role (enabled by default). <2> The `node.voting_only` role is disabled by default. <3> Disable the `node.data` role (enabled by default). <4> Disable the `node.ingest` role (enabled by default). <5> The `node.ml` role is enabled by default. <6> The `xpack.ml.enabled` setting is enabled by default. <7> Disable the `node.transform` role. <8> Disable remote cluster connections (enabled by default). [discrete] [[transform-node]] === [xpack]#{transform-cap} node# {transform-cap} nodes run {transforms} and handle {transform} API requests. If you want to use {transforms} in your cluster, you must have `node.transform` set to `true` on at least one node. This is the default behavior. If you have the {oss-dist}, do not use these settings. For more information, see <>. To create a dedicated {transform} node in the {default-dist}, set: [source,yaml] ------------------- node.master: false <1> node.voting_only: false <2> node.data: false <3> node.ingest: false <4> node.ml: false <5> node.transform: true <6> node.remote_cluster_client: false <7> ------------------- <1> Disable the `node.master` role. <2> Disable the `node.voting_only`. <3> Disable the `node.data` role. <4> Disable the `node.ingest` role. <5> Disable the `node.ml` role. <6> Enable the `node.transform` role. <7> Disable remote cluster connections. [float] [[change-node-role]] === Changing the role of a node Each data node maintains the following data on disk: * the shard data for every shard allocated to that node, * the index metadata corresponding with every shard allocated to that node, and * the cluster-wide metadata, such as settings and index templates. Similarly, each master-eligible node maintains the following data on disk: * the index metadata for every index in the cluster, and * the cluster-wide metadata, such as settings and index templates. Each node checks the contents of its data path at startup. If it discovers unexpected data then it will refuse to start. This is to avoid importing unwanted <> which can lead to a red cluster health. To be more precise, nodes with `node.data: false` will refuse to start if they find any shard data on disk at startup, and nodes with both `node.master: false` and `node.data: false` will refuse to start if they have any index metadata on disk at startup. It is possible to change the roles of a node by adjusting its `elasticsearch.yml` file and restarting it. This is known as _repurposing_ a node. In order to satisfy the checks for unexpected data described above, you must perform some extra steps to prepare a node for repurposing when setting its `node.data` or `node.master` roles to `false`: * If you want to repurpose a data node by changing `node.data` to `false` then you should first use an <> to safely migrate all the shard data onto other nodes in the cluster. * If you want to repurpose a node to have both `node.master: false` and `node.data: false` then it is simplest to start a brand-new node with an empty data path and the desired roles. You may find it safest to use an <> to migrate the shard data elsewhere in the cluster first. If it is not possible to follow these extra steps then you may be able to use the <> tool to delete any excess data that prevents a node from starting. [float] == Node data path settings [float] [[data-path]] === `path.data` Every data and master-eligible node requires access to a data directory where shards and index and cluster metadata will be stored. The `path.data` defaults to `$ES_HOME/data` but can be configured in the `elasticsearch.yml` config file an absolute path or a path relative to `$ES_HOME` as follows: [source,yaml] ----------------------- path.data: /var/elasticsearch/data ----------------------- Like all node settings, it can also be specified on the command line as: [source,sh] ----------------------- ./bin/elasticsearch -Epath.data=/var/elasticsearch/data ----------------------- TIP: When using the `.zip` or `.tar.gz` distributions, the `path.data` setting should be configured to locate the data directory outside the {es} home directory, so that the home directory can be deleted without deleting your data! The RPM and Debian distributions do this for you already. [float] [[max-local-storage-nodes]] === `node.max_local_storage_nodes` The <> can be shared by multiple nodes, even by nodes from different clusters. It is recommended however to only run one node of {es} using the same data path. This setting is deprecated in 7.x and will be removed in version 8.0. By default, {es} is configured to prevent more than one node from sharing the same data path. To allow for more than one node (e.g., on your development machine), use the setting `node.max_local_storage_nodes` and set this to a positive integer larger than one. WARNING: Never run different node types (i.e. master, data) from the same data directory. This can lead to unexpected data loss. [float] == Other node settings More node settings can be found in <>. Of particular note are the <>, the <> and the <>.