Securing Elasticsearch is crucial for protecting your data and ensuring secure communication within your Elasticsearch cluster and between clients. One of the most effective ways to achieve this is by configuring SSL/TLS encryption. This guide provides a detailed, beginner-friendly explanation of advanced SSL/TLS encryption configuration in Elasticsearch, complete with examples and outputs.

Introduction to SSL/TLS Encryption

SSL (Secure Sockets Layer) and TLS (Transport Layer Security) are cryptographic protocols designed to provide secure communication over a computer network. TLS is the successor to SSL and is more secure. In Elasticsearch, configuring SSL/TLS encryption helps to:

• Encrypt data in transit between nodes.
• Encrypt data in transit between clients and nodes.
• Ensure data integrity and prevent tampering.
• Authenticate nodes and clients.

Prerequisites

Before starting, ensure you have the following:

• Elasticsearch is installed and running.
• Basic understanding of Elasticsearch configuration files.
• OpenSSL installed for generating certificates.

Generating Certificates

Elasticsearch requires certificates for SSL/TLS encryption. You can generate these using OpenSSL or the Elasticsearch Certutil tool. We will use the Elasticsearch Certutil tool for this guide.

Step 1: Generate a Certificate Authority (CA)

First, create a Certificate Authority (CA) that will sign the certificates for your nodes.

bin/elasticsearch-certutil ca

This command will prompt you to enter a file name for the CA. For example, elastic-stack-ca.p12.

Step 2: Generate Node Certificates

Next, generate the certificates for your Elasticsearch nodes using the CA created in the previous step.

bin/elasticsearch-certutil cert --ca elastic-stack-ca.p12

This command will prompt you to enter a file name for the node certificates. For example, elastic-certificates.p12.

Step 3: Distribute Certificates

Distribute the generated elastic-certificates.p12 file to all your Elasticsearch nodes. This file contains the necessary certificates to enable SSL/TLS.

Configuring Elasticsearch for SSL/TLS

Step 1: Update Elasticsearch Configuration

Open the elasticsearch.yml configuration file on each node and add the following settings to enable SSL/TLS:

xpack.security.enabled: true

xpack.security.transport.ssl.enabled: true
xpack.security.transport.ssl.verification_mode: certificate
xpack.security.transport.ssl.keystore.path: /path/to/elastic-certificates.p12
xpack.security.transport.ssl.truststore.path: /path/to/elastic-certificates.p12

xpack.security.http.ssl.enabled: true
xpack.security.http.ssl.keystore.path: /path/to/elastic-certificates.p12
xpack.security.http.ssl.truststore.path: /path/to/elastic-certificates.p12
Replace /path/to/elastic-certificates.p12 with the actual path to your certificate file.

Step 2: Restart Elasticsearch

Restart each Elasticsearch node to apply the new configuration:

bin/elasticsearch

Verifying the SSL/TLS Configuration

To verify that SSL/TLS is correctly configured, you can use curl to make an HTTPS request to your Elasticsearch cluster.

Example Request

curl --cacert /path/to/elastic-stack-ca.crt -u elastic:password https://localhost:9200

If SSL/TLS is configured correctly, you should see a response from Elasticsearch similar to the following:

{
  "name" : "node-1",
  "cluster_name" : "my-cluster",
  "cluster_uuid" : "abcd1234",
  "version" : {
    "number" : "7.10.0",
    "build_flavor" : "default",
    "build_type" : "tar",
    "build_hash" : "abcdefg",
    "build_date" : "2020-11-10T22:14:56.825533Z",
    "build_snapshot" : false,
    "lucene_version" : "8.7.0",
    "minimum_wire_compatibility_version" : "6.8.0",
    "minimum_index_compatibility_version" : "6.0.0-beta1"
  },
  "tagline" : "You Know, for Search"
}

Configuring Client Authentication

To further secure your Elasticsearch cluster, you can configure client certificate authentication. This ensures that only clients with valid certificates can access the cluster.

Step 1: Generate Client Certificates

Use the Elasticsearch Certutil tool to generate client certificates.

bin/elasticsearch-certutil cert --ca elastic-stack-ca.p12

This command will prompt you to enter a file name for the client certificates. For example, client-certificates.p12.

Step 2: Configure Client Authentication

Open the elasticsearch.yml configuration file and add the following settings:

xpack.security.http.ssl.client_authentication: required
xpack.security.http.ssl.certificate_authorities: ["/path/to/elastic-stack-ca.crt"]

Restart Elasticsearch to apply the changes:

bin/elasticsearch

Step 3: Use Client Certificates with Curl

To make an authenticated request using client certificates, use the following curl command:

curl --cert /path/to/client.crt --key /path/to/client.key --cacert /path/to/elastic-stack-ca.crt https://localhost:9200

Configuring Kibana for SSL/TLS

If you are using Kibana with Elasticsearch, you need to configure Kibana to communicate with Elasticsearch over HTTPS.

Step 1: Update Kibana Configuration

Open the kibana.yml configuration file and add the following settings:

elasticsearch.hosts: ["https://localhost:9200"]
elasticsearch.ssl.certificateAuthorities: ["/path/to/elastic-stack-ca.crt"]
elasticsearch.username: "kibana_system"
elasticsearch.password: "password"

server.ssl.enabled: true
server.ssl.certificate: /path/to/kibana.crt
server.ssl.key: /path/to/kibana.key

Step 2: Restart Kibana

Restart Kibana to apply the new configuration:

bin/kibana

Advanced SSL/TLS Settings

Setting Up Mutual TLS

Mutual TLS (mTLS) adds an extra layer of security by requiring both server and client to authenticate each other using certificates.

Step 1: Configure Elasticsearch for mTLS

In the elasticsearch.yml file, enable client authentication:

xpack.security.http.ssl.client_authentication: required
xpack.security.http.ssl.certificate_authorities: ["/path/to/elastic-stack-ca.crt"]

Step 2: Configure Clients for mTLS

When making requests, ensure the client uses a certificate signed by the CA:

curl --cert /path/to/client.crt --key /path/to/client.key --cacert /path/to/elastic-stack-ca.crt https://localhost:9200

Tuning SSL/TLS Performance

Step 1: Enable Session Caching

Enable session caching to improve performance for repeated connections:

xpack.security.transport.ssl.session_cache_size: 1000
xpack.security.transport.ssl.session_cache_timeout: 5m

Step 2: Use Strong Cipher Suites

Ensure you use strong and secure cipher suites:

xpack.security.transport.ssl.supported_protocols: [ "TLSv1.2", "TLSv1.3" ]
xpack.security.http.ssl.supported_protocols: [ "TLSv1.2", "TLSv1.3" ]

Testing and Troubleshooting SSL/TLS

Testing SSL/TLS Configuration

You can use tools like OpenSSL to test your SSL/TLS configuration:

openssl s_client -connect localhost:9200 -CAfile /path/to/elastic-stack-ca.crt

Common Issues and Troubleshooting

Issue: Certificate Verification Failed

Ensure that the certificate paths are correct and that the certificates are valid. Use OpenSSL to check the certificate:

openssl x509 -in /path/to/elastic-stack-ca.crt -text -noout

Issue: Elasticsearch Fails to Start

Check Elasticsearch logs for error messages related to SSL configuration. Common issues include incorrect paths to certificate files or missing configuration settings.

Issue: Curl Command Fails with SSL Error

Ensure you are using the correct CA certificate and that the Elasticsearch node is accessible over HTTPS.

Conclusion

Securing Elasticsearch with advanced SSL/TLS encryption configuration is essential for protecting your data and ensuring secure communication. By following this guide, you can set up SSL/TLS encryption, configure client authentication, and tune performance settings.

This guide covered generating certificates, configuring Elasticsearch and Kibana for SSL/TLS, setting up mutual TLS, tuning performance, and troubleshooting common issues. By implementing these best practices, you can enhance the security of your Elasticsearch deployment and protect your data from unauthorized access and tampering.