Encrypting Communications in Elasticsearch

X-Pack security enables you to encrypt traffic to, from, and within your Elasticsearch cluster. Connections are secured using Transport Layer Security (TLS/SSL).

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 X-Pack security.

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

  1. Install X-Pack into Elasticsearch.
  2. Generate a private key and X.509 certificate.
  3. Configure each node to:

    1. Identify itself using its signed certificate.
    2. Required: Enable SSL on the transport layer.
    3. Recommended: Enable SSL on the HTTP layer.
  4. Restart Elasticsearch.

For more information about encrypting communications across the Elastic Stack, see Encrypting Communications.

Generating 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, certutil has been included with X-Pack. This tool takes care of generating a CA and signing certificates with the CA. certutil can be used interactively or in a silent mode through the use of an input file. The certutil tool also supports generation of certificate signing requests (CSR), so that a commercial- or organization-specific CA can be used to sign the certificates. For example:

  1. Optional: Create a certificate authority for your Elasticsearch cluster.

    For example, use the certutil ca command:

    bin/x-pack/certutil ca

    You can configure the cluster to trust all nodes that have a certificate that has been signed by this CA.

    The command outputs a single file, with a default name of elastic-stack-ca.p12. This file is a PKCS#12 keystore that contains the public certificate for your CA and the private key that is used to sign the certificates for each node.

    The certutil command also prompts you for a password to protect the file and key. If you plan to add more nodes to your cluster in the future, retain a copy of the file and remember its password.

  2. Generate a certificate and private key for each node in your cluster.

    For example, use the certutil cert command:

    bin/x-pack/certutil cert --ca elastic-stack-ca.p12

    The output is a single PKCS#12 keystore that includes the node certificate, node key, and CA certificate.

    You are also prompted for a password. You can enter a password for your certificate and key, or you can leave the password blank by pressing Enter.

    By default certutil generates certificates that have no hostname information in them (that is, they do not have any Subject Alternative Name fields). This means that you can use the certificate for every node in your cluster, but you must turn off hostname verification as shown in the configuration below.

    If you want to use hostname verification within your cluster, run the certutil cert command once for each of your nodes and provide the --name, --dns and --ip options.

    You should secure the output files, since they contain the private keys for your instance.

    Alternatively, if you want to use a commercial or organization-specific CA, you can use the certutil csr command to generate certificate signing requests (CSR) for the nodes in your cluster. For more information, see certutil.

  3. Copy the node certificate to the appropriate locations.

    Copy the applicable .p12 file into a directory within the Elasticsearch configuration directory on each node. For example, /home/es/config/certs. There is no need to copy the CA file to this directory.

    For each additional Elastic product that you want to configure, copy the certificates to the relevant configuration directory. For more information, see Enabling TLS on Elasticsearch Nodes.

If you choose not to use certutil, 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 or PKCS#12 format. Although not required, it is highly recommended that the certificate contain the DNS names and/or IP addresses of the node so that hostname verification can be used.

Enabling TLS on Elasticsearch Nodes

Once you have the signed certificate, private key, and CA certificate you need to modify the node configuration to enable Transport Layer Security (TLS/SSL).

  1. Specify the information required to access the node’s certificate.

    • If the certificate is in PKCS#12 format, add the following information to the elasticsearch.yml file on each node:

      xpack.ssl.keystore.path: certs/elastic-certificates.p12 
      xpack.ssl.truststore.path: certs/elastic-certificates.p12 

      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 certs/${node.name}.p12 format, for example.

      The certutil output includes the CA certificate inside the PKCS#12 keystore, therefore the keystore can also be used as the truststore. This name should match the keystore.path value.

    • If the certificate is in PEM format, add the following information to the elasticsearch.yml file on each node:

      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. If you secured the node’s certificate with a password, add the password to your Elasticsearch keystore:

    bin/elasticsearch-keystore add xpack.ssl.keystore.secure_password
    bin/elasticsearch-keystore add xpack.ssl.truststore.secure_password
  3. Enable TLS on the transport networking layer to ensure that communication between nodes is encrypted. Make the following changes in elasticsearch.yml:

    xpack.security.transport.ssl.enabled: true
    xpack.security.transport.ssl.verification_mode: certificate 

    If you used the --dns or --ip options with the certutil cert command and you want to enable strict hostname checking, set the verification mode to full.

  4. Optional: Enable TLS on the HTTP layer to ensure that communication between HTTP clients and the cluster is encrypted.

    Enabling TLS on the HTTP layer is strongly recommended but is not required. If you enable TLS on the HTTP layer in Elasticsearch, then you might need to make configuration changes in other parts of the Elastic Stack and in any Elasticsearch clients that you use.

    Make the following changes in elasticsearch.yml:

    xpack.security.http.ssl.enabled: true
  5. Restart Elasticsearch.

    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.

All TLS-related node settings are considered to be highly sensitive and therefore are not exposed via the nodes info API For more information about any of these settings, see Security settings.

For information about configuring other products in the Elastic Stack, see Setting Up TLS on a Cluster.