问题
Currently, we are evaluating datastax enteprise as our provider of Cassandra and Spark.We consider deploying Datastax cluster on AWS.
I have following questions:
1) In step 1 of Datastax on EC2 installation manual, I need to choose correct AMI Image: Currently there are 7 of them. Which is the correct one: (DataStax Auto-Clustering AMI 2.5.1-pv, DataStax Auto-Clustering AMI 2.6.3-1204-pv, DataStax Auto-Clustering AMI 2.6.3-1404-pv....)
2) The moment we launch the cluster, do we pay only for aws instances or also Datastax Enterprise licensing fee? I know there is a 30 days enterprise free trial, but nowhere in the installation process I saw a step where we can ask for the free trial? Is there some online calculator that we can use to calculate the cost of a cluster on a monthy basis (based on the instance types we create)
3) In the step 3 of the installation process Configure Instance Details, I am confused with terms instance and nodes. What is the difference between them? What happens if I choose:
a) 1 instance, --totalnodes 3 (in the user data)
b) 3 instance, --tatalnodes 3
c) 1 instance, --totalnodes 0 --analyticsnodes 3
d) 3 instance, --totalnodes 0 --analyticsnodes 3
4) We are interested in the use case where each of our 3 cassandra nodes has Spark. Is the proper user data configuration: --totalnodes 0 --analyticsnodes 3 Are then we going to have 0 nodes with only cassandra, and 3 nodes that have Cassandra and Spark? What is the Number of instances we should specify then?
5) In step 4 of installation process Add Storage, we are asked to add storage to the instance. But why do we need this storage? When choosing instance type, for example m3.large, I already know that my instance has 32GB of SSD storage, what is this then?
Thank you for your answers. If there is some email list to which I can send these questions, I would appreciate it.
回答1:
Use whichever AMI has the highest version number and the virtualization type you prefer (-pv or -hvm): http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/virtualization_types.html
You only pay for EC2 usage. DSE is free for testing and development. You do not need to request a trial license. If you want a production license or if you want to become a startup member, contact DataStax.
The AMI will install one "DSE node" per "EC2 instance". So if you want a six node cluster you need to specify 6 instances. To use your examples:
a) 1 instance, --totalnodes 3 (in the user data)
- This won't work
b) 3 instance, --tatalnodes 3
This will give you a three node Cassandra cluster (running on three instances). You have not specified search or analytics nodes so by default you will just get Cassandra nodes.
c) 1 instance, --totalnodes 0 --analyticsnodes 3
Won't work. Total nodes should equal number of instances and number of analytics nodes can't be greater than total nodes.
d) 3 instance, --totalnodes 0 --analyticsnodes 3
Won't work. Number of analytics nodes can't be greater than number of total nodes.
If you want a three-node cluster and you want all of them running both Cassandra and Spark use this:
3 instances, --totalnodes 3 --analyticsnodes 3
Adding storage is optional. And only possible with certain instance types. You should notice with m3.large that there is a default config and you can't actually make any changes to it.
Hope this helps!
来源：https://stackoverflow.com/questions/37482585/datastaxenteprise-node-vs-instance-correct-ami-image-why-do-i-need-storage