[role="xpack"]
[[tls-transport]]
==== Encrypting communications between nodes in a cluster

The transport networking layer is used for internal communication between nodes
in a cluster. When {security-features} are enabled, you must use TLS to ensure
that communication between the nodes is encrypted.

. <<node-certificates,Generate node certificates>>.

. Enable TLS and specify the information required to access the node’s
certificate.

** If the signed certificate is in PKCS#12 format, add the following information to the
`elasticsearch.yml` file on each node:
+
--
[source,yaml]
-----------------------------------------------------------
xpack.security.transport.ssl.enabled: true
xpack.security.transport.ssl.verification_mode: certificate <1>
xpack.security.transport.ssl.keystore.path: elastic-certificates.p12 <2>
xpack.security.transport.ssl.truststore.path: elastic-certificates.p12 <3>
-----------------------------------------------------------
<1> If you used the `--dns` or `--ip` options with the `elasticsearch-certutil cert` command
and you want to enable strict hostname checking, set the verification mode to
`full`.
See <<ssl-tls-settings, `xpack.security.transport.ssl.verification_mode`>> for a description of these values.

<2> If you created a separate certificate for each node, then you might need to
customize this path on each node. If the filename matches the node name, you can
use the `${node.name}.p12` format, for example.
<3> The `elasticsearch-certutil` outputs a PKCS#12 keystore which includes the
CA certificate as a trusted certificate entry. This allows for the keystore to
also be used as a truststore. In this case, the path value should match
the `keystore.path` value.
Note, however, that this is not the general rule. There are keystores that cannot be
used as truststores, only 
{ref}/security-settings.html#pkcs12-truststore-note[specifically crafted ones can]
--

** If the certificate is in PEM format, add the following information to the
`elasticsearch.yml` file on each node:
+
--
[source, yaml]
--------------------------------------------------
xpack.security.transport.ssl.enabled: true
xpack.security.transport.ssl.verification_mode: certificate <1>
xpack.security.transport.ssl.key: /home/es/config/node01.key <2>
xpack.security.transport.ssl.certificate: /home/es/config/node01.crt <3>
xpack.security.transport.ssl.certificate_authorities: [ "/home/es/config/ca.crt" ] <4>
--------------------------------------------------
<1> If you used the `--dns` or `--ip` options with the `elasticsearch-certutil cert` command
and you want to enable strict hostname checking, set the verification mode to
`full`.
See <<ssl-tls-settings, `xpack.security.transport.ssl.verification_mode`>> for a description of these values.
<2> The full path to the node key file. This must be a location within the
    {es} configuration directory.
<3> The full path to the node certificate. This must be a location within the
    {es} configuration directory.
<4> An array of paths to the CA certificates that should be trusted. These paths
    must be a location within the {es} configuration directory.
--

. If you secured the node's certificate with a password, add the password to
your {es} keystore:

** If the signed certificate is in PKCS#12 format, use the following commands:
+
--
[source,shell]
-----------------------------------------------------------
bin/elasticsearch-keystore add xpack.security.transport.ssl.keystore.secure_password

bin/elasticsearch-keystore add xpack.security.transport.ssl.truststore.secure_password
-----------------------------------------------------------
--

** If the certificate is in PEM format, use the following commands:
+
--
[source,shell]
-----------------------------------------------------------
bin/elasticsearch-keystore add xpack.security.transport.ssl.secure_key_passphrase
-----------------------------------------------------------
--

. Restart {es}.
+
--
You must perform a full cluster restart. Nodes which are configured to use TLS
cannot communicate with nodes that are using unencrypted networking (and
vice-versa). After enabling TLS you must restart all nodes in order to maintain
communication across the cluster.
--

[NOTE]
===============================
* All TLS-related node settings are considered to be highly sensitive and
therefore are not exposed via the
{ref}/cluster-nodes-info.html#cluster-nodes-info[nodes info API] For more
information about any of these settings, see <<security-settings>>.

* {es} monitors all files such as certificates, keys, keystores, or truststores 
that are configured as values of TLS-related node settings. If you update any of 
these files (for example, when your hostnames change or your certificates are 
due to expire), {es} reloads them. The files are polled for changes at 
a frequency determined by the global {es} `resource.reload.interval.high` 
setting, which defaults to 5 seconds.
===============================