public String getReleaseVersion() {
        return this.releaseVersion;
    }
<p>
If the node group was deployed using a launch template with a custom AMI, then this is the AMI ID that was
specified in the launch template. For node groups that weren't deployed using a launch template, this is the
version of the Amazon EKS optimized AMI that the node group was deployed with.
</p>

@return If the node group was deployed using a launch template with a custom AMI, then this is the AMI ID that
        was specified in the launch template. For node groups that weren't deployed using a launch template, this
        is the version of the Amazon EKS optimized AMI that the node group was deployed with.
aws-java-sdk-eks/src/main/java/com/amazonaws/services/eks/model/Nodegroup.java