[[modules-network]]
=== Networking

Each {es} node has two different network interfaces. Clients send requests to
{es}'s REST APIs using its <<http-settings,HTTP interface>>, but nodes
communicate with other nodes using the <<transport-settings,transport
interface>>. The transport interface is also used for communication with
<<remote-clusters,remote clusters>>.

You can configure both of these interfaces at the same time using the
`network.*` settings. If you have a more complicated network, you might need to
configure the interfaces independently using the `http.*` and `transport.*`
settings. Where possible, use the `network.*` settings that apply to both
interfaces to simplify your configuration and reduce duplication.

By default {es} binds only to `localhost` which means it cannot be accessed
remotely. This configuration is sufficient for a local development cluster made
of one or more nodes all running on the same host. To form a cluster across
multiple hosts, or which is accessible to remote clients, you must adjust some
<<common-network-settings,network settings>> such as `network.host`.

[WARNING]
.Be careful with the network configuration!
=============================
Never expose an unprotected node to the public internet. If you do, you are
permitting anyone in the world to download, modify, or delete any of the data
in your cluster.
=============================

Configuring {es} to bind to a non-local address will <<dev-vs-prod,convert some
warnings into fatal exceptions>>. If a node refuses to start after configuring
its network settings then you must address the logged exceptions before
proceeding.

[[common-network-settings]]
==== Commonly used network settings

Most users will need to configure only the following network settings.

`network.host`::
(<<static-cluster-setting,Static>>, string)
Sets the address of this node for both HTTP and transport traffic. The node
will bind to this address and will also use it as its publish address. Accepts
an IP address, a hostname, or a <<network-interface-values,special value>>.
+
Defaults to `_local_`. However, note that <<configuring-stack-security,security
auto-configuration>> will add `http.host: 0.0.0.0` to your `elasticsearch.yml`
configuration file, which overrides this default for HTTP traffic.

`http.port`::
(<<static-cluster-setting,Static>>, integer)
The port to bind for HTTP client communication. Accepts a single value or a
range. If a range is specified, the node will bind to the first available port
in the range.
+
Defaults to `9200-9300`.

`transport.port`::
(<<static-cluster-setting,Static>>, integer)
The port to bind for communication between nodes. Accepts a single value or a
range. If a range is specified, the node will bind to the first available port
in the range. Set this setting to a single port, not a range, on every
master-eligible node.
+
Defaults to `9300-9400`.

[[remote_cluster.port]]
`remote_cluster.port`::
(<<static-cluster-setting,Static>>, integer)
The port to bind for remote cluster client communication. Accepts a single value.
+
Defaults to `9443`.

[[network-interface-values]]
==== Special values for network addresses

You can configure {es} to automatically determine its addresses by using the
following special values. Use these values when configuring
`network.host`, `network.bind_host`, `network.publish_host`, and the
corresponding settings for the HTTP and transport interfaces.

`_local_`::
  Any loopback addresses on the system, for example `127.0.0.1`.

`_site_`::
  Any site-local addresses on the system, for example `192.168.0.1`.

`_global_`::
  Any globally-scoped addresses on the system, for example `8.8.8.8`.

`_[networkInterface]_`::
  Use the addresses of the network interface called `[networkInterface]`. For
  example if you wish to use the addresses of an interface called `en0` then
  set `network.host: _en0_`.

`0.0.0.0`::
  The addresses of all available network interfaces.

NOTE: In some systems these special values resolve to multiple addresses. If
so, {es} will select one of them as its publish address and may change its
selection on each node restart. Ensure your node is accessible at every possible
address.

NOTE: Any values containing a `:` (e.g. an IPv6 address or some of the
<<network-interface-values,special values>>) must be quoted because `:` is a
special character in YAML.

[[network-interface-values-ipv4-vs-ipv6]]
===== IPv4 vs IPv6

These special values yield both IPv4 and IPv6 addresses by default, but you can
also add an `:ipv4` or `:ipv6` suffix to limit them to just IPv4 or IPv6
addresses respectively. For example, `network.host: "_en0:ipv4_"` would set this
node's addresses to the IPv4 addresses of interface `en0`.

[TIP]
.Discovery in the Cloud
================================

More special settings are available when running in the Cloud with either the
{plugins}/discovery-ec2.html[EC2 discovery plugin] or the
{plugins}/discovery-gce-network-host.html#discovery-gce-network-host[Google Compute Engine discovery plugin]
installed.

================================

[[modules-network-binding-publishing]]
==== Binding and publishing

{es} uses network addresses for two distinct purposes known as binding and
publishing. Most nodes will use the same address for everything, but more
complicated setups may need to configure different addresses for different
purposes.

When an application such as {es} wishes to receive network communications, it
must indicate to the operating system the address or addresses whose traffic it
should receive. This is known as _binding_ to those addresses. {es} can bind to
more than one address if needed, but most nodes only bind to a single address.
{es} can only bind to an address if it is running on a host that has a network
interface with that address. If necessary, you can configure the transport and
HTTP interfaces to bind to different addresses.

Each {es} node has an address at which clients and other nodes can contact it,
known as its _publish address_. Each node has one publish address for its HTTP
interface and one for its transport interface. These two addresses can be
anything, and don't need to be addresses of the network interfaces on the host.
The only requirements are that each node must be:

* Accessible at its HTTP publish address by all clients that will discover it
  using sniffing.

* Accessible at its transport publish address by all other nodes in its
  cluster, and by any remote clusters that will discover it using
  <<sniff-mode>>.

If you specify the transport publish address using a hostname then {es} will
resolve this hostname to an IP address once during startup, and other nodes
will use the resulting IP address instead of resolving the name again
themselves. To avoid confusion, use a hostname which resolves to the node's
address in all network locations.

===== Using a single address

The most common configuration is for {es} to bind to a single address at which
it is accessible to clients and other nodes. In this configuration you should
just set `network.host` to that address. You should not separately set any bind
or publish addresses, nor should you separately configure the addresses for the
HTTP or transport interfaces.

===== Using multiple addresses

Use the <<advanced-network-settings, advanced network settings>> if you wish to
bind {es} to multiple addresses, or to publish a different address from the
addresses to which you are binding. Set `network.bind_host` to the bind
addresses, and `network.publish_host` to the address at which this node is
exposed. In complex configurations, you can configure these addresses
differently for the HTTP and transport interfaces.

[[advanced-network-settings]]
==== Advanced network settings

These advanced settings let you bind to multiple addresses, or to use different
addresses for binding and publishing. They are not required in most cases and
you should not use them if you can use the <<common-network-settings,commonly
used settings>> instead.

`network.bind_host`::
(<<static-cluster-setting,Static>>, string)
The network address(es) to which the node should bind in order to listen for
incoming connections. Accepts a list of IP addresses, hostnames, and
<<network-interface-values,special values>>. Defaults to the address given by
`network.host`. Use this setting only if binding to multiple addresses or using
different addresses for publishing and binding.

`network.publish_host`::
(<<static-cluster-setting,Static>>, string)
The network address that clients and other nodes can use to contact this node.
Accepts an IP address, a hostname, or a <<network-interface-values,special
value>>. Defaults to the address given by `network.host`. Use this setting only
if binding to multiple addresses or using different addresses for publishing
and binding.

NOTE: You can specify a list of addresses for `network.host` and
`network.publish_host`. You can also specify one or more hostnames or
<<network-interface-values,special values>> that resolve to multiple addresses.
If you do this then {es} chooses one of the addresses for its publish address.
This choice uses heuristics based on IPv4/IPv6 stack preference and
reachability and may change when the node restarts. Ensure
each node is accessible at all possible publish addresses.

[[tcp-settings]]
===== Advanced TCP settings

Use the following settings to control the low-level parameters of the TCP
connections used by the HTTP and transport interfaces.

`network.tcp.keep_alive`::
(<<static-cluster-setting,Static>>, boolean)
Configures the `SO_KEEPALIVE` option for network sockets, which determines
whether each connection sends TCP keepalive probes. Defaults to `true`.

`network.tcp.keep_idle`::
(<<static-cluster-setting,Static>>, integer)
Configures the `TCP_KEEPIDLE` option for network sockets, which determines the
time in seconds that a connection must be idle before starting to send TCP
keepalive probes. Defaults to `-1`, which means to use the system default. This
value cannot exceed `300` seconds. Only applicable on Linux and macOS.

`network.tcp.keep_interval`::
(<<static-cluster-setting,Static>>, integer)
Configures the `TCP_KEEPINTVL` option for network sockets, which determines the
time in seconds between sending TCP keepalive probes. Defaults to `-1`, which
means to use the system default. This value cannot exceed `300` seconds. Only
applicable on Linux and macOS.

`network.tcp.keep_count`::
(<<static-cluster-setting,Static>>, integer)
Configures the `TCP_KEEPCNT` option for network sockets, which determines the
number of unacknowledged TCP keepalive probes that may be sent on a connection
before it is dropped. Defaults to `-1`, which means to use the system default.
Only applicable on Linux and macOS.

`network.tcp.no_delay`::
(<<static-cluster-setting,Static>>, boolean)
Configures the `TCP_NODELAY` option on network sockets, which determines
whether {wikipedia}/Nagle%27s_algorithm[TCP no delay] is enabled. Defaults to
`true`.

`network.tcp.reuse_address`::
(<<static-cluster-setting,Static>>, boolean)
Configures the `SO_REUSEADDR` option for network sockets, which determines
whether the address can be reused or not. Defaults to `false` on Windows and
`true` otherwise.

`network.tcp.send_buffer_size`::
(<<static-cluster-setting,Static>>, <<byte-units,byte value>>)
Configures the size of the TCP send buffer for network sockets. Defaults to
`-1` which means to use the system default.

`network.tcp.receive_buffer_size`::
(<<static-cluster-setting,Static>>, <<byte-units,byte value>>)
Configures the size of the TCP receive buffer. Defaults to `-1` which means to
use the system default.

include::http.asciidoc[]

include::transport.asciidoc[]

include::remote-cluster-network.asciidoc[]

include::network/tracers.asciidoc[]

include::network/threading.asciidoc[]
