Troubleshooting TLS Failures

TLS ensures encrypted communication between Redis clients and servers. In Redis Software, TLS errors commonly result from certificate mismatches, incorrect client configurations, unsupported protocol versions, or misaligned cipher suites. This guide walks through a systematic approach to identifying and resolving TLS failures. Key sections include Step-by-Step Troubleshooting, Common Error Patterns and Fixes, and Helpful CLI Examples.

Step-by-Step Troubleshooting

1. Identify Symptoms

Typical TLS failure messages include:

• SSL handshake failed, wrong version number, tlsv1 alert, certificate verify failed

• Unrecognized option or bad number of args for: '--tls' (client misconfiguration)

• Errors can be logged in redis-server, event_log.log, dmcproxy.log, or cluster_wd.log

Use supervisorctl status and rladmin status to check server component health.

2. Verify redis-cli Has TLS Support

Run from your client host when building: make BUILD_TLS=yes

To ensure you're using a TLS-enabled build of redis-cli to test TLS connections.

3. Confirm Redis Enterprise TLS Configuration

Use rladmin to verify whether TLS is enabled for a database or endpoint.

• Run:

  rladmin status endpoints

  • Check the SSL column:

    • All means TLS is enforced for all connections.

    • Replica means TLS is used only for replica connections.

    • No means TLS is not enabled.

To view additional TLS-related cluster-level configuration:

• Refer to:

  rladmin info cluster

  • This provides information on the cluster’s configuration, including TLS-related aspects (cipher suites, minimum TLS versions, etc.).

For full instructions on enabling and configuring TLS in Redis Software, see:
Enable TLS – Redis Docs

For broader deployment guidance, review Redis Security Best Practices.

4. Run a Basic redis-cli Test

For non-client authenticated (mTLS) connections:

For mutual TLS (mTLS):

redis-cli -h <hostname> -p <port> --tls \
 --cacert proxy_cert.pem \
 --cert redis_user.crt \
 --key redis_user_private.key

5. Check Network and DNS Resolution

From the client host, run:

Validate that the Redis endpoint resolves correctly and is reachable over the network.

6. Validate Certificates

• Verify expiration:

  openssl x509 -in redis.crt -noout -enddate

• Check key strength (RHEL9/OpenSSL 3.0+ requires ≥2048-bit RSA keys):

  openssl rsa -in redis.key -text -noout

For more command options, see OpenSSL CLI Reference

Important: Weak keys will cause hard failures with no workaround—replace with 2048-bit or stronger keys.

For details on enforced key requirements, see RHEL 9 System Crypto Policies.

7. Cross-Check Protocol and Cipher Compatibility

Redis Software may reject clients if their TLS protocol version or cipher suites do not match cluster requirements.

View current TLS and cipher configuration:

rladmin info cluster

• Review:

  • min_data_TLS_version

  • min_control_TLS_version

  • data_cipher_list

  • control_cipher_suites or cipher_suites (depends on version)

If clients are failing due to mismatched TLS or ciphers, you may need to update cluster settings.
Refer to:

• Configure TLS protocol

• Configure cipher suites

Certificate Authority Managed Internode TLS Behavior

Beginning with Redis Software 8, clusters that use customer-managed internode TLS certificates must ensure that all nodes share a consistent CA chain to maintain connectivity.
If nodes fail to join, replace, or establish intra-cluster TLS handshakes, verify:

• The CA chain is identical across all participating nodes.

• Any rotated or renewed certificates have propagated to every node in the cluster.

Clusters that previously relied on self-signed internode certificates may require updated trust stores when transitioning to CA-issued certificates.
This validation prevents handshake failures and node rejoin errors after upgrades or certificate rotations.

Read more on Customer-provided certificates for internode encryption 

Common TLS Errors and Fixes

Helpful TLS Diagnostic CLI Commands

# Test connectivity using OpenSSL
openssl s_client -connect <host>:<port> -CAfile /path/to/ca.crt

# Check cert expiration
openssl x509 -in server.crt -noout -enddate

# Check key strength
openssl rsa -in server.key -text -noout

# Inspect Redis cluster TLS settings
rladmin cluster config