[[ssl-tls]]
=== Setting Up SSL/TLS on a Cluster

{security} enables you to encrypt traffic to, from, and within your Elasticsearch
cluster. Connections are secured using Transport Layer Security (TLS), which is
commonly referred to as "SSL".

WARNING: Clusters that do not have encryption enabled send all data in plain text
including passwords and will not be able to install a license that enables {security}.

To enable encryption, you need to perform the following steps on each node in
the cluster:

. <<installing-node-certificates, Generate a private key and X.509 certificate>>.

. <<configure-ssl, Configure the node>> to:
.. Identify itself using its signed certificate.
.. Enable SSL on the transport and HTTP layers.

. Restart Elasticsearch.

[[installing-node-certificates]]
==== Node Certificates

TLS requires X.509 certificates to perform encryption and authentication of the application
that is being communicated with. In order for the communication between nodes to be truly
secure, the certificates must be validated. The recommended approach for validating
certificate authenticity in a Elasticsearch cluster is to trust the certificate authority (CA)
that signed the certificate. By doing this, as nodes are added to your cluster they just need
to use a certificate signed by the same CA and the node is automatically allowed to join the
cluster. Additionally, it is recommended that the certificates contain subject alternative
names (SAN) that correspond to the node's ip address and dns name so that hostname verification
can be performed.

In order to simplify the process of generating certificates for the Elastic Stack, a command
line tool, `certgen` has been included with {xpack}. This tool takes care of the generating
a CA and signing certificates with the CA. `certgen` can be used interactively or in a silent
mode through the use of an input file. The `certgen` tool also supports generation of certificate
signing requests (CSR), so that a commercial or organization specific CA may be used to sign
the certificates. For more information, see {ref}/certgen.html[certgen].

NOTE: If you choose not to use `certgen`, the certificates that you obtain must allow for both
`clientAuth` and `serverAuth` if the extended key usage extension is present. The certificates
need to be in PEM format. Although not required, it is highly recommended that the certificate contain
the dns name(s) and/or ip address(es) of the node so that hostname verification may be used.

[[enable-ssl]]
==== Enabling SSL in the Node Configuration

Once you have the signed certificate, private key, and CA certificate you need to
modify the node configuration to enable SSL.

[[configure-ssl]]
To enable SSL, make the following changes in `elasticsearch.yml`:

. Specify the location of the node's keystore and the password(s) needed to
access the node's certificate. For example:
+
--
[source, yaml]
--------------------------------------------------
xpack.ssl.key:                     /home/es/config/x-pack/node01.key <1>
xpack.ssl.certificate:             /home/es/config/x-pack/node01.crt <2>
xpack.ssl.certificate_authorities: [ "/home/es/config/x-pack/ca.crt" ] <3>
--------------------------------------------------
<1> The full path to the node key file. This must be a location within the
    Elasticsearch configuration directory.
<2> The full path to the node certificate. This must be a location within the
    Elasticsearch configuration directory.
<3> An array of paths to the CA certificates that should be trusted. These paths
    must be a location within the Elasticsearch configuration directory.
--

. Enable SSL on the transport networking layer to ensure that communication
between nodes is encrypted:
+
[source, yaml]
--------------------------------------------------
xpack.security.transport.ssl.enabled: true
--------------------------------------------------
+
. Enable SSL on the HTTP layer to ensure that communication between HTTP clients
and the cluster is encrypted:
+
[source, yaml]
--------------------------------------------------
xpack.security.http.ssl.enabled: true
--------------------------------------------------
+

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

NOTE: All SSL related node settings that are considered to be highly sensitive
      and therefore are not exposed via the
      {ref}/cluster-nodes-info.html#cluster-nodes-info[nodes info API].