Implementing SSL and High Availability in a Multi-Node OpenSearch Cluster

Problem:

A financial services client encountered critical SSL-related errors while deploying a two-node OpenSearch 1.3.6 cluster for high availability. Despite both nodes appearing operational, accessing indices or interacting with the cluster through a Java application resulted in errors such as:

• SSLHandshakeException: Insufficient buffer remaining for AEAD cipher fragment
• IBMCertPathBuilderException: unable to find valid certification path to requested target

The deployment was initially configured with demo certificates and then attempted with Venafi-generated JKS certificates. Configuration mismatches, certificate trust issues, and improper file permissions created persistent errors during node startup and communication, halting production deployment.

Process:

Step 1: Initial Troubleshooting

The support team began by analyzing logs and configuration files. It was quickly identified that an unsupported Java version and incomplete SSL certificate chain were causing the initial errors. They advised switching to Java 11 and explicitly setting TLSv1.2 in the configuration.

Step 2: Certificate Verification

Subsequent issues included curl errors like unable to get local issuer certificate and security plugin errors due to improper certificate signing. The team recommended replacing demo certs with signed ones from Venafi and ensuring both nodes trusted each other’s certificates through correct keystore and truststore configuration.

Step 3: Debugging Node Communication

Despite certificate updates, handshake errors persisted. The support expert discovered:

• Wildcard certificates (e.g., CN=*.smbcgroup.com) were required to avoid SAN mismatch errors.
• Config files needed to be nearly identical except for node.name and network.host.
• Truststore mismatches and incorrect OID/DNS values in certificates prevented secure transport communication.

Step 4: Security Index Initialization

A critical step — initializing the security index — had been missed. The support team guided the client through executing the securityadmin.sh script with correct parameters and certificate files. This enabled user management APIs and resolved internal security module load errors.

Step 5: Final Hardening and Validation

After further collaboration, the expert helped the client:

• Generate wildcard certificates using the provided script with custom CSR parameters.
• Ensure identical opensearch.yml configurations across nodes except for node name and host.
• Set file permissions and group memberships correctly for certificate access.

The client was also advised to delete the data folder before restarts to avoid UUID mismatches.

Solution:

Through methodical troubleshooting and precise configuration changes, the support team guided the client in building a secure and functional OpenSearch cluster. The issues related to certificate trust, host mismatches, permission errors, and uninitialized security plugins were systematically resolved. The final cluster was validated as healthy (status: green) with both nodes functioning securely.

All configuration changes and certificate generation steps were documented and shared to support future deployments and avoid similar errors.

Conclusion:

Implementing SSL in a multi-node OpenSearch setup requires meticulous attention to certificate signing, hostname consistency, and config symmetry. The client’s attempt to secure their cluster with Venafi certificates introduced complex challenges – all of which were resolved through collaborative troubleshooting, correct security index initialization, and use of wildcard certificates. This case underscores the importance of aligning OpenSearch security practices with real-world certificate authority constraints and ensuring consistency across cluster nodes.