If your primary objective is to setup a simple Cassandra cluster, then you probably want to start here:
However, if you have an existing AWS cluster to which you want to add Cassandra, then read on.
In my case, I wanted to add Cassandra to an existing HPCC cluster. More specifically, I wanted to be able to spin-up an HPCC + Cassandra cluster with a single command. To accomplish this, I decided to add a bit of python scripting on top of Cloud Formation.
Amazon has a facility called Cloud Formation. Cloud Formation reads a JSON template file, and creates instances as described in that file. (pretty slick) Within that JSON, you can execute shell commands that do the heavy lifting. The JSON file can define parameters that the administrator can then provide via the management console, or via AWS CLI.
(IMHO, I suggest installing AWS CLI)
Running a Cloud FormationFirst, I started with Tim Humphrie's EasyFastHPCCoAWS. That cloud formation template is a great basis. It installs AWS CLI, and copies the contents of an S3 bucket down into /home/ec2-users. Have a look at the template file. To get that up and running, it is a simple matter of creating a PlacementGroup, a KeyPair, and an S3 bucket, into which you copy the contents of the github repo. For simplicity, I named all of those the same thing: "realtime-hpcc".
Now, with a single command, I can fire up a low-cost HPCC cluster with the following:
Note, I specified the template via https url. I also specified a stack-name, which is what you'll use when querying AWS for status, which you can do with the following command:
With that you get a nice, clean JSON back that looks something like this:
The "StackStatus" is the key property. You'll want to wait until that says, "CREATE_COMPLETE".
Once it completes, you can go into the management console and see your EC2 instances.
If something went wrong, you can go have a look in /var/log/user-data.log. Tim's template conveniently redirects the output of the shell commands to that log file.
Installing CassandraNOW -- to actually get Cassandra installed on the machines, I simply forked Tim's work and altered the Cloud Formation template to include the datastax repo and a yum install of Cassandra. And the next time I created my cluster: poof magic voodoo, Cassandra was installed!
Next I needed to configure the Cassandra instances into a cluster. At first, I tried to do this using a shell script executed as part of the cloud formation, but that proved difficult because I wanted the IP addresses for all the nodes, not just the one on which the script was running. I shifted gears and decided to orchestrate the configuration from python after the cloud had already formed.
I wrote a quick little python script (configure_local_cassandra.py) that takes four parameters: the location of the cassandra.yaml file, the cluster name, the private IPs of the Cassandra nodes, and the IP of the node itself. The python script updates the cassandra config, substituting those values into the template file. I added this to the S3 bucket, and Cloud Formation took care of deploying the template and the python script to the machines. (thanks to Tim's template)
Configuring CassandraWith that script and the template in place on each machine, the final piece is the script that gathers the IP addresses for the nodes and calls the python script via ssh. For this, we use the aws ec2 cli, and fetch the JSON for all of our instances. The aws ec2 command looks like this:
I wrote a python script (configure_cassandra_cluster.py) that parses that JSON and run commands on each of the nodes via ssh.
To make everything simple, I added a bunch of shell scripts that wrap all the command lines (so I don't need to remember all the parameters). The shell scripts are as follow
To keep simple, I also added a bunch of shell scripts that wrap all the command lines (so I don't need to remember all the parameters). The shell scripts allow you to create a cluster, get the status of a cluster, and delete a cluster using a single command line:
create_stack.sh, get_status.sh, delete_stack.sh
Putting it all together...
To summarize, the create_stack.sh script uses aws cloudformation to create the cluster.
Then, you can watch the status of the cluster with, get_status.sh.
Once formed, the configure_cassandra_cluster.py script installs, configures and starts Cassandra.
After that, you should be able to run ecl using Casssandra!
Feel free to take these scripts, and apply them to other things. And kudos to Tim Humphries for the cloud formation template.