This section summarizes our best practices and provides our recommendations for using OPDK with AWS cloud.
Cassandra is used as a backend and datastore for almost all the policies and is a critical part of the Apigee Edge runtime environment. This document focuses on optimizing Casssandra for the AWS environment.
Storage and I/O requirements
Most Cassandra I/O is sequential, but there are cases where you require random I/O. An example is when reading Sorted String Tables during read operations. SSD is the recommended storage mechanism for Cassandra, because it provides extremely low-latency response times for random read operations while supplying enough sequential write performance for compaction operations. Replication is also taken into consideration here.
Many instances in AWS EC2 comes with local storage in which the hard drive is physically attached to the hardware that the EC2 instance is hosted on. Apigee recommends leveraging both SSD and instance stores when running Cassandra in production. When you use an instance type with more than 1 SSD, you can use RAID0 to get more throughput and storage capacity.
Cassandra uses the Gossip protocol to exchange information with other nodes about network topology. The use of Gossip plus the distributed nature of Cassandra — which involves talking to multiple nodes for read and write operations — results in a lot of data transfer through the network. Apigee recommends using Instance type with at least 1Gbps network bandwidth and more than 1Gbps for production systems.
Use a VPC with CIDR of /16. Since subnets in AWS cannot span across more than 1 AZ, Apigee recommends the following:
- Create 1 subnet per Availability Zone (AZ)
- Use 3 private subnets for your Apigee installation, with one Cassandra node in each AZ. The 3 subnets should have enough CIDR blocks to accommodate horizontal expansion of the Cassandra cluster.
- Configure 3 public subnets with dedicated NAT for Cassandra to be able to talk to the internet for software download and security updates.
Unlike legacy master-slave architectures, Cassandra has a master-less architecture in which all nodes play an identical role, so there is no single point of failure. Consider spreading your Cassandra nodes across multiple AZs to enable high availability. By spreading nodes across AZs, you can still maintain availability and uptime in the case of disaster.
Choosing an instance family
When looking at Cassandra CPU requirements, it's useful to note that insert-heavy workloads are CPU-bound in Cassandra before becoming IO-bound. In other words, all write operations go to the commit log, but Cassandra is so efficient in writing that the CPU becomes the limiting factor. Cassandra is highly concurrent and uses as many CPU cores as available.
Apigee recommends using an instance family, which has a balance of both CPU and memory. Specifically, we recommend using C5 family instances if available in your AWS region and C3 as a fall back option. In some cases, 4xlarge is the optimal instance in both families that provides the best price/performance.
Apigee also recommends using a default tenancy for Cassandra instances. When you scale to more than 1 instance per AZ, most likely all your Cassandra instances will be placed on the same underlying hardware if you set tenancy to be dedicated. So, when hardware fails, you will likely lose all your instances in that AZ.
The following table summarizes the Apigee recommendations for using AWS with Apigee Edge for Private Cloud:
|Instance Family||C5d (preferred ) or C3|
|Instance Store||SSD (local storage) with RAID0|
|Node Placement||1 Cassandra node per AZ|
|VPC and Subnet||1 subnet per AZ and a VPC per region|
For more information, see Amazon instance types.