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Transport

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Transport

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The transport module is used for internal communication between nodes within the cluster. Each call that goes from one node to the other uses the transport module (for example, when an HTTP GET request is processed by one node, and should actually be processed by another node that holds the data).

The transport mechanism is completely asynchronous in nature, meaning that there is no blocking thread waiting for a response. The benefit of using asynchronous communication is first solving the C10k problem, as well as being the ideal solution for scatter (broadcast) / gather operations such as search in Elasticsearch.

TCP Transport

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The TCP transport is an implementation of the transport module using TCP. It allows for the following settings:

Setting	Description
`transport.tcp.port`	A bind port range. Defaults to `9300-9400`.
`transport.publish_port`	The port that other nodes in the cluster should use when communicating with this node. Useful when a cluster node is behind a proxy or firewall and the `transport.tcp.port` is not directly addressable from the outside. Defaults to the actual port assigned via `transport.tcp.port`.
`transport.bind_host`	The host address to bind the transport service to. Defaults to `transport.host` (if set) or `network.bind_host`.
`transport.publish_host`	The host address to publish for nodes in the cluster to connect to. Defaults to `transport.host` (if set) or `network.publish_host`.
`transport.host`	Used to set the `transport.bind_host` and the `transport.publish_host` Defaults to `transport.host` or `network.host`.
`transport.tcp.connect_timeout`	The socket connect timeout setting (in time setting format). Defaults to `30s`.
`transport.tcp.compress`	Set to `true` to enable compression (LZF) between all nodes. Defaults to `false`.
`transport.ping_schedule`	Schedule a regular application-level ping message to ensure that transport connections between nodes are kept alive. Defaults to `5s` in the transport client and `-1` (disabled) elsewhere. It is preferable to correctly configure TCP keep-alives instead of using this feature, because TCP keep-alives apply to all kinds of long-lived connection and not just to transport connections.

It also uses the common network settings.

TCP Transport Profiles

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Elasticsearch allows you to bind to multiple ports on different interfaces by the use of transport profiles. See this example configuration

transport.profiles.default.port: 9300-9400
transport.profiles.default.bind_host: 10.0.0.1
transport.profiles.client.port: 9500-9600
transport.profiles.client.bind_host: 192.168.0.1
transport.profiles.dmz.port: 9700-9800
transport.profiles.dmz.bind_host: 172.16.1.2

The default profile is special. It is used as a fallback for any other profiles, if those do not have a specific configuration setting set, and is how this node connects to other nodes in the cluster.

The following parameters can be configured on each transport profile, as in the example above:

port: The port to bind to
bind_host: The host to bind
publish_host: The host which is published in informational APIs
tcp_no_delay: Configures the TCP_NO_DELAY option for this socket
tcp_keep_alive: Configures the SO_KEEPALIVE option for this socket
reuse_address: Configures the SO_REUSEADDR option for this socket
tcp_send_buffer_size: Configures the send buffer size of the socket
tcp_receive_buffer_size: Configures the receive buffer size of the socket

Long-lived idle connections

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Elasticsearch opens a number of long-lived TCP connections between each pair of nodes in the cluster, and some of these connections may be idle for an extended period of time. Nonetheless, Elasticsearch requires these connections to remain open, and it can disrupt the operation of the cluster if any inter-node connections are closed by an external influence such as a firewall. It is important to configure your network to preserve long-lived idle connections between Elasticsearch nodes, for instance by leaving tcp_keep_alive enabled and ensuring that the keepalive interval is shorter than any timeout that might cause idle connections to be closed, or by setting transport.ping_schedule if keepalives cannot be configured.

Transport Tracer

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The transport module has a dedicated tracer logger which, when activated, logs incoming and out going requests. The log can be dynamically activated by settings the level of the org.elasticsearch.transport.TransportService.tracer logger to TRACE:

PUT _cluster/settings
{
   "transient" : {
      "logger.org.elasticsearch.transport.TransportService.tracer" : "TRACE"
   }
}

You can also control which actions will be traced, using a set of include and exclude wildcard patterns. By default every request will be traced except for fault detection pings:

PUT _cluster/settings
{
   "transient" : {
      "transport.tracer.include" : "*",
      "transport.tracer.exclude" : "internal:discovery/zen/fd*"
   }
}

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