[[modules-transport]]
== Transport

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
http://en.wikipedia.org/wiki/C10k_problem[C10k problem], as well as
being the ideal solution for scatter (broadcast) / gather operations such
as search in ElasticSearch.

[float]
=== TCP Transport

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

[cols="<,<",options="header",]
|=======================================================================
|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`.
|=======================================================================

It also uses the common
<<modules-network,network settings>>.

[float]
=== Local Transport

This is a handy transport to use when running integration tests within
the JVM. It is automatically enabled when using
`NodeBuilder#local(true)`.