Logstash Error: SSL Handshake Error - Common Causes & Fixes

Brief Explanation

An SSL Handshake Error in Logstash occurs when there's a problem establishing a secure SSL/TLS connection between Logstash and another service or component. This error indicates that the SSL/TLS negotiation process failed, preventing encrypted communication.

Common Causes

1. Mismatched SSL/TLS versions
2. Invalid or expired SSL certificates
3. Incorrect certificate authority (CA) configuration
4. Hostname verification failures
5. Firewall or network issues blocking SSL/TLS traffic

Troubleshooting and Resolution Steps

1. Verify SSL/TLS versions:

   • Ensure both Logstash and the remote service support compatible SSL/TLS versions
   • Update to the latest versions if possible

2. Check certificate validity:

   • Verify that the SSL certificates are valid and not expired
   • Ensure the certificate's Common Name (CN) or Subject Alternative Name (SAN) matches the hostname

3. Review CA configuration:

   • Confirm that the correct CA certificates are installed and configured in Logstash
   • Verify the trust chain is complete and valid

4. Enable hostname verification:

   • Set ssl_verify_mode to full in your Logstash configuration
   • Ensure the hostname in the certificate matches the connection hostname

5. Investigate network issues:

   • Check firewall rules to allow SSL/TLS traffic on required ports
   • Verify network connectivity between Logstash and the remote service

6. Enable debug logging:

   • Set log.level: debug in logstash.yml
   • Analyze the debug logs for detailed SSL/TLS negotiation information

7. Use OpenSSL for testing:

   • Run openssl s_client -connect host:port to test SSL/TLS connectivity
   • Analyze the output for any certificate or handshake issues

Best Practices

• Regularly update Logstash and related components to ensure up-to-date SSL/TLS support
• Use strong cipher suites and disable outdated SSL/TLS versions
• Implement proper certificate management, including timely renewals
• Use hostname verification to prevent man-in-the-middle attacks
• Monitor SSL/TLS connections and set up alerts for certificate expiration

Frequently Asked Questions

Q: How can I check if my SSL certificate is valid?
A: You can use the OpenSSL command line tool: openssl x509 -in certificate.pem -text -noout. This will display the certificate details, including validity dates and subject information.

Q: What SSL/TLS versions should I use with Logstash?
A: It's recommended to use TLS 1.2 or higher. Avoid using SSL 3.0 and TLS 1.0 as they have known vulnerabilities.

Q: How do I enable debug logging for SSL/TLS in Logstash?
A: Set log.level: debug in your logstash.yml file. You can also add --log.level=debug to your Logstash command line arguments.

Q: Can I use self-signed certificates with Logstash?
A: Yes, but it's not recommended for production environments. If you must use self-signed certificates, ensure you properly configure the trust store in Logstash to recognize the certificate.

Q: How often should I rotate my SSL certificates?
A: Best practice is to rotate SSL certificates annually or more frequently. Many organizations opt for automated certificate management with shorter lifespans, such as 90 days, to enhance security.