Connect to Elastic Cache Cluster

It appears you're having trouble connecting to your ElastiCache cluster using the redis-cli command, but you're able to connect using telnet. This situation suggests a few potential issues and solutions:

1. TLS/SSL requirement: ElastiCache, especially for serverless configurations, often requires TLS encryption for connections. Try adding the --tls flag to your redis-cli command:

   src/redis-cli -c -h ENDPOINT -p 6379 --tls

2. Security group settings: Ensure that the security group associated with your ElastiCache cluster allows inbound traffic on port 6379 from your client's IP address or security group.

3. Network configuration: Verify that your client (likely an EC2 instance) is in the same VPC as the ElastiCache cluster, or that proper VPC peering and routing are set up if they're in different VPCs.

4. Cluster mode: The -c flag in your command suggests you're trying to connect to a cluster in cluster mode. Make sure your cluster is indeed configured for cluster mode, otherwise try removing the -c flag.

5. Redis version compatibility: Ensure that your redis-cli version is compatible with the Redis version running on your ElastiCache cluster.

If telnet is working but redis-cli is not, it suggests that network connectivity is established, but there might be an issue with the Redis protocol handshake or authentication. Double-check any authentication requirements for your cluster.

For further troubleshooting, you can try:

• Using verbose mode with redis-cli (add -v flag) to get more detailed output about the connection process.
• Checking ElastiCache logs for any error messages related to connection attempts.
• Verifying that the ENDPOINT you're using is correct and up-to-date.

If problems persist, you may need to review your ElastiCache configuration settings or consult AWS support for more specific assistance.
Sources
AWS port forwarding session does not work for redis cluster with cluster mode | AWS re:Post
Unable to connect to Redis through redis-cli | AWS re:Post
Not Able to connect Redis serverless Endpoint in ec2 ubuntu in same VPC | AWS re:Post