Setting Up SSL/TLS on a Cluster

X-Pack 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:

  1. Generate a private key and X.509 certificate.
  2. Configure the node to:

    1. Identify itself using its signed certificate.
    2. Enable SSL on the transport and HTTP layers.
  3. Restart Elasticsearch.

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 X-Pack. 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 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:

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 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:

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:

instances:
  - name: "node1" 
    ip: 
      - "192.0.2.1"
    dns: 
      - "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" 

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.

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.

An optional array of strings that represent DNS names for this instance. The values will be added as Subject Alternative Names.

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:

bin/x-pack/certgen -in instances.yml 

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.

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.

To enable SSL, make the following changes in elasticsearch.yml:

  1. Specify the location of the node’s keystore and the password(s) needed to access the node’s certificate. For example:

    xpack.ssl.key:                     /home/es/config/x-pack/node01.key 
    xpack.ssl.certificate:             /home/es/config/x-pack/node01.crt 
    xpack.ssl.certificate_authorities: [ "/home/es/config/x-pack/ca.crt" ] 

    The full path to the node key file. This must be a location within the Elasticsearch configuration directory.

    The full path to the node certificate. This must be a location within the Elasticsearch configuration directory.

    An array of paths to the CA certificates that should be trusted. These paths must be a location within the Elasticsearch configuration directory.

  2. Enable SSL on the transport networking layer to ensure that communication between nodes is encrypted:

    xpack.security.transport.ssl.enabled: true
  3. Enable SSL on the HTTP layer to ensure that communication between HTTP clients and the cluster is encrypted:

    xpack.security.http.ssl.enabled: true
  4. Restart Elasticsearch.
Note

All SSL related node settings that are considered to be highly sensitive and therefore are not exposed via the nodes info API.