Planning a DataStax Enterprise cluster on Amazon EC2

DataStax AMI deployments

DataStax no longer hosts the DataStax ComboAMI. You can install DataStax Enterprise in two ways:

Create your instances using an AMI for a supported platform and from a trusted source. Then use the appropriate install method for your platform.
Use the Lifecycle Manager in OpsCenter to easily provision a DataStax Enterprise cluster for versions 4.7 and later:
1. Create your instances using an AMI for a supported platform and from a trusted source.
2. Use the Lifecycle Manager to provision and configure your cluster.

Use AMIs from trusted sources

Use only AMIs for supported platforms and from a trusted source. Random AMIs pose a security risk and may perform slower than expected due to the way the EC2 install is configured. The following are examples of trusted AMIs:

EC2 deployments for multiple regions/availability zones

For these deployments use any of the supported platforms on each node:

It is best practice to use the same platform on all nodes. If your cluster was instantiated using the DataStax AMI (no longer supported), use Ubuntu for the additional nodes. Configure the cluster as a multiple datacenter cluster using the Ec2MultiRegionSnitch.

Guidelines for production clusters

For production clusters on EC2, use these guidelines for choosing the instance types:

Development and light production: m3.large
Moderate production: m3.xlarge
SSD production with light data: c3.2xlarge
Largest heavy production: m3.2xlarge (PV) or i2.2xlarge (HVM)
Micro, small, and medium types are not supported.

Note: The main difference between m1 and m3 instance types for use with DataStax Enterprise is that m3 instance types have faster, smaller SSD drives and m1 instance types have slower, larger rotational drives. Use m1 instance types when you have higher tolerance for latency SLAs and you require smaller cluster sizes, or both. For more aggressive workloads use m3 instance types with appropriately sized clusters.

EBS volumes recommended for production

SSD-backed general purpose volumes (GP2) or provisioned IOPS volumes (PIOPS) are suitable for production workloads. These volume types are designed to deliver consistent, low latency performance:

GP2	PIOPS
The best choice for most workloads and have the advantage of guaranteeing 10,000 IOPS when volumes larger than 3.5TB are attached to instances. Designed to deliver single-digit millisecond latencies. Designed to deliver the provisioned performance 99.0% of the time.	Designed to deliver single-digit millisecond latencies. Designed to deliver the provisioned performance 99.9% of the time.

EBS magnetic volumes not recommended

EBS magnetic volumes are not recommended for DataStax Enterprise data storage volumes for the following reasons:

EBS magnetic volumes contend directly for network throughput with standard packets. This contention means that EBS throughput is likely to fail when a network link is saturated.
EBS magnetic volumes have unreliable performance. I/O performance can be exceptionally slow, causing the system to back load reads and writes until the entire cluster becomes unresponsive.
Adding capacity by increasing the number of EBS volumes per host does not scale. You can easily surpass the ability of the system to keep effective buffer caches and concurrently serve requests for all of the data it is responsible for managing.

Note: Use only ephemeral instance-store or the recommended EBS volume types for DataStax Enterprise data storage.

For more information and graphs related to ephemeral versus EBS performance, see Systematic Look at EC2 I/O.

Disk Performance Optimization

To ensure high disk performance to mounted drives, it is recommended that you pre-warm your drives by writing once to every drive location before production use. Depending on EC2 conditions, you can get moderate to enormous increases in throughput. See Optimizing Disk Performance in the Amazon Elastic Compute Cloud Documentation.

Storage recommendations

DataStax Enterprise supports JBOD (just a bunch of disks). JBOD excels at tolerating partial failures in a disk array. Configure using the in the cassandra.yaml file. Addition information is available in the Handling Disk Failures In Cassandra 1.2 blog and Recovering from a single disk failure using JBOD.

Note: JBOD support allows you to use standard disks. However, RAID0 may provide better throughput because it splits every block to be on another device. This means that writes are written in parallel fashion instead of written serially on disk.

EC2 security group

When deploying DataStax Enterprise on EC2, you must create security rules that open ports to other nodes in the same security group. An EC2 Security Group acts as a firewall that allows you to choose which protocols and ports are open in your cluster. You can specify the protocols and ports either by a range of IP addresses or by security group. For more information, see the Amazon EC2 help on Security Groups.

Warning: Specifying a Source IP of 0.0.0.0/0 opens externally accessible ports to incoming traffic from any IP address. The risk of data loss is high.

The Securing DataStax Enterprise ports table provides a list of ports that should be opened to internode and client communications.

Note: Generally, when you have firewalls between machines, it is difficult to run JMX across a network and maintain security. This is because JMX connects on port 7199, handshakes, and then uses any port within the 1024+ range. Instead use SSH to execute commands remotely to connect to JMX locally or use the DataStax OpsCenter.