Performance: 

- Automatic detection and recovery from cache node failures
- Automatic discovery of nodes within a cluster enabled for automatic discovery, so that no changes need to be made to your application when you add or remove nodes
- Integration with other AWS services such as Amazon EC2, Amazon CloudWatch, AWS CloudTrail, and Amazon SNS to provide a secure, high-performance, managed in-memory caching solution
- Each cache node has its own Domain Name Service (DNS) name and port

Scalability: 

- Every node runing an instance of Memcached can scale the nodes in a cluster up or down to a different instance type
- Memcached supports up to 300 nodes per customer for each AWS Region with each cluster having 1–40 nodes
- More than 40 nodes in a Memcached cluster, or more than 300 nodes totalFill out the ElastiCache Limit Increase Request form at: https://aws.amazon.com/contact-us/elasticache-node-limit-request/

Availability:

- Flexible Availability Zone placement of nodes and clusters
- Amazon ElastiCache for Memcached is available in multiple AWS Regions around the world
- It's recommended to use consistent hashing while partitioning data
- When you scale your Memcached cluster up or down, you must create a new cluster. Memcached clusters always start out empty unless your application populates it

Security: 

- All new ElastiCache clusters are launched in an Amazon Virtual Private Cloud (Amazon VPC) environment
- ElastiCache node access is restricted to applications running on whitelisted Amazon EC2 instances
- Access to cluster outside a VPC is controlled by security groups
- AWS is responsible for protecting the infrastructure that runs AWS services in the AWS Cloud
- You are also responsible for other factors including the sensitivity of your data
- Your company’s requirements, and applicable laws and regulations

Performance: 

- Redis (cluster mode enabled) supports partitioning your data across up to 500 shards.
- Integration with other AWS services such as Amazon EC2, Amazon CloudWatch, AWS CloudTrail, and Amazon SNS. This integration helps provide a managed in-memory caching solution that is high-performance and highly secure.
- ElastiCache for Redis manages backups, software patching, automatic failure detection, and recovery.
- You can have automated backups performed when you need them, or manually create your own backup snapshot. You can use these backups to restore a cluster. The ElastiCache for Redis restore process works reliably and efficiently.
- Data tiering provides a price-performance option for Redis workloads by utilizing lower-cost solid state drives (SSDs) in each cluster node in addition to storing data in memory. It is ideal for workloads that access up to 20 percent of their overall dataset regularly, and for applications that can tolerate additional latency when accessing data on SSD.

Scalability: 

- Automatic detection of and recovery from cache node failures
- You can get high availability with a primary instance and a synchronous secondary instance that you can fail over to when problems occur. You can also use read replicas to increase read scaling
- Redis (cluster mode enabled) clusters can have up to 500 shards

Availability: 

- Multi-AZ for a failed primary cluster to a read replica, in Redis clusters that support replication
- Flexible Availability Zone placement of nodes and clusters for increased fault tolerance
- By using the Global Datastore for Redis feature, you can work with fully managed, fast, reliable, and secure replication across AWS Regions. Using this feature, you can create cross-Region read replica clusters for ElastiCache for Redis to enable low-latency reads and disaster recovery across AWS Regions

Security: 

- For Redis version 3.2 and later, all versions support encryption in transit and encryption at rest encryption with authentication. This support helps you build HIPAA-compliant applications
- You can control access to your ElastiCache for Redis clusters by using AWS Identity and Access Management to define users and permissions
- All new ElastiCache clusters are launched in an Amazon Virtual Private Cloud (Amazon VPC) environment
- ElastiCache node access is restricted to applications running on whitelisted Amazon EC2 instances
- Access to cluster outside a VPC is controlled by security groups
- AWS is responsible for protecting the infrastructure that runs AWS services in the AWS Cloud
- You are also responsible for other factors including the sensitivity of your data
- Your company’s requirements, and applicable laws and regulations

resource "aws_elasticache_cluster" "memcached_engine" {
  cluster_id           = "cluster-memcached"
  engine               = "memcached"
  node_type            = "cache.m4.large"
  num_cache_nodes      = 4
  parameter_group_name = "default.memcached1.4"
  port                 = 11211
}

resource "aws_elasticache_cluster" "redis_engine" {
  cluster_id           = "cluster-redis"
  engine               = "redis"
  node_type            = "cache.m4.large"
  num_cache_nodes      = 2
  parameter_group_name = "default.redis3.2"
  engine_version       = "3.2.10"
  port                 = 6379
}

https://docs.aws.amazon.com/ElastiCache/latest/developerguide/limits.html 

https://en.wikipedia.org/wiki/Amazon_ElastiCache