[[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.

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.

NOTE: If you choose not to use the `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.

[[generating-signed-certificates]]
===== Generating Certificates with `certgen`

The `certgen` tool can be used to generate a CA and signed certificates for your nodes. The tool
can be used interactively:

[listing]
....
bin/x-pack/certgen
This tool assists you in the generation of X.509 certificates and certificate
signing requests for use with SSL in the Elastic stack. Depending on the command
line option specified, you may be prompted for the following:

* The path to the output file
    * The output file is a zip file containing the signed certificates and
      private keys for each instance. If a Certificate Authority was generated,
      the certificate and private key will also be included in the output file.
* Information about each instance
    * An instance is any piece of the Elastic Stack that requires a SSL certificate.
      Depending on your configuration, Elasticsearch, Logstash, Kibana, and Beats
      may all require a certificate and private key.
    * The minimum required value for each instance is a name. This can simply be the
      hostname, which will be used as the Common Name of the certificate. A full
      distinguished name may also be used.
    * IP addresses and DNS names are optional. Multiple values can be specified as a
      comma separated string. If no IP addresses or DNS names are provided, you may
      disable hostname verification in your SSL configuration.
* Certificate Authority private key password
    * The password may be left empty if desired.

Let's get started...

Please enter the desired output file [/home/es/config/x-pack/certificate-bundle.zip]:
Enter instance name: node01
Enter name for directories and files [node01]:
Enter IP Addresses for instance (comma-separated if more than one) []: 10.10.0.1
Enter DNS names for instance (comma-separated if more than one) []: node01.mydomain.com,node01
Would you like to specify another instance? Press 'y' to continue entering instance information: y
Enter instance name: node02
Enter name for directories and files [node02]:
Enter IP Addresses for instance (comma-separated if more than one) []: 10.10.0.2
Enter DNS names for instance (comma-separated if more than one) []: node02.mydomain.com
Would you like to specify another instance? Press 'y' to continue entering instance information:
Certificates written to /Users/jmodi/dev/tmp/elasticsearch-5.0.0-alpha5-SNAPSHOT/config/x-pack/certificate-bundle.zip

This file should be properly secured as it contains the private keys for all
instances and the certificate authority.

After unzipping the file, there will be a directory for each instance containing
the certificate and private key. Copy the certificate, key, and CA certificate
to the configuration directory of the Elastic product that they will be used for
and follow the SSL configuration instructions in the product guide.

For client applications, you may only need to copy the CA certificate and
configure the client to trust this certificate.
....

The usage of `certgen` above generates a zip file with the CA certificate, private key, two signed certificates and keys
in PEM format for `node01` and `node02`.

[[generating-csr]]
===== Generating Certificate Signing Requests with `certgen`

When using a commercial or organization specific CA, the `certgen` tool may be used to generate
certificate signing requests (CSR) for the nodes in your cluster:

[listing]
....
bin/x-pack/certgen -csr
This tool assists you in the generation of X.509 certificates and certificate
signing requests for use with SSL in the Elastic stack. Depending on the command
line option specified, you may be prompted for the following:

* The path to the output file
    * The output file is a zip file containing the certificate signing requests
      and private keys for each instance.
* Information about each instance
    * An instance is any piece of the Elastic Stack that requires a SSL certificate.
      Depending on your configuration, Elasticsearch, Logstash, Kibana, and Beats
      may all require a certificate and private key.
    * The minimum required value for each instance is a name. This can simply be the
      hostname, which will be used as the Common Name of the certificate. A full
      distinguished name may also be used.
    * IP addresses and DNS names are optional. Multiple values can be specified as a
      comma separated string. If no IP addresses or DNS names are provided, you may
      disable hostname verification in your SSL configuration.

Let's get started...

Please enter the desired output file [/home/es/config/x-pack/csr-bundle.zip]:
Enter instance name: node01
Enter name for directories and files [node01]:
Enter IP Addresses for instance (comma-separated if more than one) []: 10.10.0.1
Enter DNS names for instance (comma-separated if more than one) []: node01.mydomain.com,node01
Would you like to specify another instance? Press 'y' to continue entering instance information: y
Enter instance name: node02
Enter name for directories and files [node02]:
Enter IP Addresses for instance (comma-separated if more than one) []: 10.10.0.2
Enter DNS names for instance (comma-separated if more than one) []: node02.mydomain.com
Would you like to specify another instance? Press 'y' to continue entering instance information:
Certificate signing requests written to /Users/jmodi/dev/tmp/elasticsearch-5.0.0-alpha5-SNAPSHOT/config/x-pack/csr-bundle.zip

This file should be properly secured as it contains the private keys for all
instances.

After unzipping the file, there will be a directory for each instance containing
the certificate signing request and the private key. Provide the certificate
signing requests to your certificate authority. Once you have received the
signed certificate, copy the signed certificate, key, and CA certificate to the
configuration directory of the Elastic product that they will be used for and
follow the SSL configuration instructions in the product guide.
....

The usage of `certgen` above generates a zip file with two CSRs and private
keys. The CSRs should be provided to the CA in order to obtain the signed
certificates. The signed certificates will need to be in PEM format in order to
be used.

===== Using `certgen` in Silent Mode

`certgen` supports a silent mode of operation to enable easier batch operations. In order
to use this mode, a YAML file containing the information about the instances needs to be
created matching the format shown below:

[source, yaml]
--------------------------------------------------
instances:
  - name: "node1" <1>
    ip: <2>
      - "192.0.2.1"
    dns: <3>
      - "node1.mydomain.com"
  - name: "node2"
    ip:
      - "192.0.2.2"
      - "198.51.100.1"
  - name: "node3"
  - name: "node4"
    dns:
      - "node4.mydomain.com"
      - "node4.internal"
  - name: "CN=node5,OU=IT,DC=mydomain,DC=com"
    filename: "node5" <4>
--------------------------------------------------
<1> The name of the instance. This can be a simple string value or can be a Distinguished Name (DN). This is the only required field.
<2> An optional array of strings that represent IP Addresses for this instance. Both IPv4 and IPv6 values are allowed. The values will
be added as Subject Alternative Names.
<3> An optional array of strings that represent DNS names for this instance. The values will be added as Subject Alternative Names.
<4> The filename to use for this instance. This name will be the name of the directory in the zip file that this instance's files will
stored in and it will used be used in the naming of the files within the directory. This filename should not have an extension. Note: If
the `name` provided for the instance does not represent a valid filename, then the `filename` field must be present.

With the YAML file ready, the `certgen` tool can be used to generate certificates or certificate signing requests. Simply pass the file's
path to `certgen` using the `-in` option. For example:

[source, sh]
--------------------------------------------------
bin/x-pack/certgen -in instances.yml <1>
--------------------------------------------------
<1> Generates a CA certificate and private key in addition to certificates and private keys for the instances
contained in the YAML file. The other options to the tool can be specified in addition to the `-in` option. For all of the available
options, run `bin/x-pack/certgen -h`.

[[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.

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].
