On April 2, 2026, Amazon Web Services introduced Amazon ElastiCache Serverless now supports IPv6 and dual stack connectivity, adding support for IPv6 and dual stack connectivity on ElastiCache Serverless. This expands beyond the previous IPv4-only model and allows a cache to accept connections over both IPv4 and IPv6 simultaneously, enabling more flexible connectivity patterns.
In this post, I put the new dual stack capability to the test by verifying IPv4 and IPv6 connectivity on ElastiCache Serverless.
Setup
I started by enabling IPv6 at the VPC level by attaching an Amazon-provided IPv6 CIDR block, allowing resources inside the VPC to communicate over IPv6.
I then deployed an ElastiCache Serverless instance and selected dual stack as the Network Type during creation. This option was introduced in the April 2 update and allows the cache to handle both IPv4 and IPv6 connections at the same time. The selected subnets must support both IPv4 and IPv6 address space for this configuration to work.
Verification
From an EC2 instance with IPv6 enabled, I first verified that the cache resolves to an IPv6 address:
nslookup -type=AAAA <cache-endpoint>
Output:
The result shows AAAA records, indicating that the cache is reachable over IPv6.
Next, I validated connectivity using the approach recommended by Amazon Web Services for ElastiCache Serverless, using openssl s_client with filtered output for clarity.
IPv6 Connectivity
openssl s_client -connect <cache-endpoint>:6379 -6 2>&1 | grep -E "Connecting|CONNECTED|Verification|Protocol"
Output:
The CONNECTED status confirms that a TCP connection is successfully established, while Verification: OK indicates that the TLS certificate is valid.
IPv4 Connectivity
openssl s_client -connect <cache-endpoint>:6379 -4 2>&1 | grep -E "Connecting|CONNECTED|Verification|Protocol"
Output:
The IPv4 test also succeeds, showing that the same cache is reachable over IPv4 with a valid TLS session.
Analysis
From this test, the dual stack capability in Amazon ElastiCache Serverless works exactly as described by Amazon Web Services. The cache resolves to an IPv6 address and accepts TLS connections over both IPv6 and IPv4 simultaneously from the same endpoint. This reflects a gradual migration path where IPv6 can be introduced alongside IPv4 traffic without impacting existing application connectivity.
Beyond dual stack, IPv6-only configuration is also supported as a separate option, allowing workloads that fully transition to IPv6 to operate without relying on IPv4 addressing.
Conclusion
Based on this hands-on test, the dual stack capability in ElastiCache Serverless performs well in real usage. The same cache can be accessed over IPv4 and IPv6, with both paths functioning as expected, and this capability is available at no additional charge across all AWS Regions, making it easy to adopt IPv6 in existing ElastiCache Serverless workloads as part of a gradual transition.
