Elasticsearch SSLException: SSL handshake failed - Common Causes & Fixes

Brief Explanation

The "SSLException: SSL handshake failed" error in Elasticsearch occurs when there's a problem establishing a secure SSL/TLS connection between Elasticsearch nodes or between a client and the Elasticsearch cluster. This error indicates that the SSL handshake process, which is crucial for setting up a secure communication channel, has failed.

Common Causes

1. Mismatched SSL/TLS versions
2. Expired or invalid SSL certificates
3. Incorrect certificate configuration
4. Hostname verification failures
5. Incompatible cipher suites
6. Firewall or network issues blocking SSL traffic

Troubleshooting and Resolution Steps

1. Verify SSL certificate validity:

   • Check expiration dates
   • Ensure certificates are issued by a trusted Certificate Authority (CA)

2. Confirm SSL/TLS version compatibility:

   • Ensure all nodes and clients use compatible SSL/TLS versions
   • Consider upgrading to the latest TLS version for better security

3. Review Elasticsearch SSL configuration:

   • Check elasticsearch.yml for correct SSL settings
   • Verify paths to keystore and truststore files

4. Validate hostname verification:

   • Ensure certificate Common Name (CN) or Subject Alternative Name (SAN) matches the hostname

5. Check network and firewall settings:

   • Confirm SSL ports (usually 9200 for HTTP and 9300 for transport) are open
   • Verify no firewall rules are blocking SSL traffic

6. Analyze Elasticsearch logs:

   • Look for detailed SSL-related error messages
   • Use debug logging for more information on SSL handshake process

7. Test SSL connection manually:

   • Use tools like openssl s_client to test SSL handshake

8. Update cipher suites if necessary:

   • Ensure compatible and secure cipher suites are enabled

Best Practices

• Regularly update and rotate SSL certificates
• Use strong, industry-standard encryption algorithms
• Implement proper certificate management processes
• Monitor SSL certificate expiration dates
• Use tools like Certbot for automatic certificate renewal
• Implement mutual TLS (mTLS) for enhanced security when appropriate

Frequently Asked Questions

Q: How can I check if my SSL certificate is valid?
A: You can use the openssl command to verify a certificate's validity. Run openssl x509 -in certificate.pem -text -noout to view certificate details, including expiration date.

Q: What SSL/TLS version should I use with Elasticsearch?
A: It's recommended to use TLS 1.2 or higher. Elasticsearch 7.x and above support TLS 1.3, which provides better security and performance.

Q: Can SSL handshake failures be caused by clock synchronization issues?
A: Yes, if the system clocks are significantly out of sync, it can cause SSL handshake failures due to certificate validation issues. Ensure all systems have synchronized time, preferably using NTP.

Q: How do I enable debug logging for SSL in Elasticsearch?
A: Add logger.org.elasticsearch.xpack.security: DEBUG to your log4j2.properties file to enable detailed SSL-related logging.

Q: Is it possible to use self-signed certificates with Elasticsearch?
A: Yes, you can use self-signed certificates, but it's not recommended for production environments. If you must use them, ensure all nodes and clients trust these certificates explicitly.