Saturday, March 4, 2017

Running the Cassandra Database as a systemd service

Running the Cassandra Database as a systemd service

If the Cassandra Database stops for whatever reason, systemd can attempt to restart it. The systemd unit file can ensure that our Cassandra service stays running. The systemd-cloud-watch utility will be sure to log all restarts to AWS CloudWatch.
Here is the systemd unit file for Cassandra.


Description=Cassandra Service


ExecStartPre=- /sbin/swapoff -a
ExecStartPre=- /bin/chown -R cassandra /opt/cassandra
ExecStart=/opt/cassandra/bin/cassandra  -p /opt/cassandra/PID


The above will tells systemd to restart the Cassandra Database in one minute if it goes down. Since we are using OS log aggregation to AWS Cloudwatch every time Cassandra goes down or is restarted by systemd, we will get log messages that we can create alerts and trigger in CloudWatch to then run AWS Lambdas that work with the rest of the AWS ecosystem. Critical bugs in queries or UDF or UFA could cause Cassandra to go down. These could be hard to track down and sporadic. Logging aggregation helps.

Redux - Past Articles in this Cassandra Tutorial: Cassandra Cluster DevOps/DBA series

The first article in this Cassandra tutorial series was about setting up a Cassandra cluster with Vagrant (also appeared on DZone with some additional content DZone Setting up a Cassandra Cluster with Vagrant. The second article in this series was about setting up SSL for a Cassandra cluster using Vagrant (which also appeared with more content as DZone Setting up a Cassandra Cluster with SSL). The third article in this series was about configuring and using Ansible (building on the first two articles). This article (the 4th) will cover applying the tools and techniques from the first three articles to produce an image (EC2 AMI to be precise) that we can deploy to AWS/EC2. To do this explanation, we will use Packer, Ansible, and the Aws Command Line tools. The AWS command line tools are essential for doing DevOps with AWS.

Check out more information about the Cassandra Database

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