[[modules-transport]]
=== Transport

REST clients send requests to your {es} cluster over <<modules-http,HTTP>>, but
the node that receives a client request cannot always handle it alone and must
normally pass it on to other nodes for further processing. It does this using
the transport networking layer. The transport layer is used for all internal
communication between nodes within a cluster, all communication with the nodes
of a <<modules-remote-clusters,remote cluster>>, and also by the
`TransportClient` in the {es} Java API.

[[transport-settings]]
==== Transport settings

The following settings can be configured for the internal transport that
communicates over TCP. These settings also use the common
<<modules-network,network settings>>.

`transport.port`::
(<<static-cluster-setting,Static>>)
A bind port range. Defaults to `9300-9400`.

`transport.publish_port`::
(<<static-cluster-setting,Static>>)
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.port` is not directly
addressable from the outside. Defaults to the actual port assigned via
`transport.port`.

`transport.bind_host`::
(<<static-cluster-setting,Static>>)
The host address to bind the transport service to. Defaults to
`transport.host` (if set) or `network.bind_host`.

`transport.publish_host`::
(<<static-cluster-setting,Static>>)
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`::
(<<static-cluster-setting,Static>>)
Used to set the `transport.bind_host` and the `transport.publish_host`.

`transport.connect_timeout`::
(<<static-cluster-setting,Static>>)
The connect timeout for initiating a new connection (in
time setting format). Defaults to `30s`.

`transport.compress`::
(<<static-cluster-setting,Static>>)
Set to `true` to enable compression (`DEFLATE`) between
all nodes. Defaults to `false`.

`transport.ping_schedule`::
(<<static-cluster-setting,Static>>)
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 connections and not just to
transport connections.

`transport.tcp.no_delay`::
(<<static-cluster-setting,Static>>)
Enable or disable the {wikipedia}/Nagle%27s_algorithm[TCP no delay]
setting. Defaults to `network.tcp.no_delay`.

`transport.tcp.keep_alive`::
(<<static-cluster-setting,Static>>)
Configures the `SO_KEEPALIVE` option for this socket, which
determines whether it sends TCP keepalive probes.
Defaults to `network.tcp.keep_alive`.

`transport.tcp.keep_idle`::
(<<static-cluster-setting,Static>>)
Configures the `TCP_KEEPIDLE` option for this socket, which
determines the time in seconds that a connection must be idle before
starting to send TCP keepalive probes. Defaults to `network.tcp.keep_idle` if set,
or the system default otherwise.
This value cannot exceed `300` seconds. In cases where the system default
is higher than `300`, the value is automatically lowered to `300`. Only applicable on
Linux and macOS, and requires Java 11 or newer.

`transport.tcp.keep_interval`::
(<<static-cluster-setting,Static>>)
Configures the `TCP_KEEPINTVL` option for this socket,
which determines the time in seconds between sending TCP keepalive probes.
Defaults to `network.tcp.keep_interval` if set, or the system default otherwise.
This value cannot exceed `300` seconds. In cases where the system default is higher than `300`,
the value is automatically lowered to `300`. Only applicable on Linux and macOS,
and requires Java 11 or newer.

`transport.tcp.keep_count`::
(<<static-cluster-setting,Static>>)
Configures the `TCP_KEEPCNT` option for this socket, which
determines the number of unacknowledged TCP keepalive probes that may be
sent on a connection before it is dropped. Defaults to `network.tcp.keep_count`
if set, or the system default otherwise. Only applicable on Linux and macOS, and
requires Java 11 or newer.

`transport.tcp.reuse_address`::
(<<static-cluster-setting,Static>>)
Should an address be reused or not. Defaults to `network.tcp.reuse_address`.

`transport.tcp.send_buffer_size`::
(<<static-cluster-setting,Static>>)
The size of the TCP send buffer (specified with <<size-units,size units>>).
Defaults to `network.tcp.send_buffer_size`.

`transport.tcp.receive_buffer_size`::
(<<static-cluster-setting,Static>>)
The size of the TCP receive buffer (specified with <<size-units,size units>>).
Defaults to `network.tcp.receive_buffer_size`.

[[transport-profiles]]
===== Transport profiles

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

[source,yaml]
--------------
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 which to bind.
* `bind_host`: The host to which to bind.
* `publish_host`: The host which is published in informational APIs.

Profiles also support all the other transport settings specified in the
<<transport-settings,transport settings>> section, and use these as defaults.
For example, `transport.profiles.client.tcp.reuse_address` can be explicitly
configured, and defaults otherwise to `transport.tcp.reuse_address`.

[[long-lived-connections]]
===== Long-lived idle connections

A transport connection between two nodes is made up of a number of long-lived
TCP connections, some of which may be idle for an extended period of time.
Nonetheless, Elasticsearch requires these connections to remain open, and it
can disrupt the operation of your 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. Devices which drop connections when they reach
a certain age are a common source of problems to Elasticsearch clusters, and
must not be used.

[[request-compression]]
===== Request compression

By default, the `transport.compress` setting is `false` and network-level
request compression is disabled between nodes in the cluster. This default
normally makes sense for local cluster communication as compression has a
noticeable CPU cost and local clusters tend to be set up with fast network
connections between nodes.

The `transport.compress` setting always configures local cluster request
compression and is the fallback setting for remote cluster request compression.
If you want to configure remote request compression differently than local
request compression, you can set it on a per-remote cluster basis using the
<<remote-cluster-settings,`cluster.remote.${cluster_alias}.transport.compress` setting>>.


[[response-compression]]
===== Response compression

The compression settings do not configure compression for responses. {es} will
compress a response if the inbound request was compressed--even when compression
is not enabled. Similarly, {es} will not compress a response if the inbound
request was uncompressed--even when compression is enabled.


[[transport-tracer]]
==== Transport tracer

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

[source,console]
--------------------------------------------------
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:

[source,console]
--------------------------------------------------
PUT _cluster/settings
{
   "transient" : {
      "transport.tracer.include" : "*",
      "transport.tracer.exclude" : "internal:coordination/fault_detection/*"
   }
}
--------------------------------------------------
