We live in a world of process isolation and tools that make utilizing it extremely simple, with apps like Docker we can perform dependency management with dependency isolation. As I am slowly becoming a fanboy of containerization, I look forward to the day when typing ps on my local workstation or remote server is nearly synonymous with commands like docker ps or kubectl get services.
Case: Cassandra development and your local workstation.
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I use Apache Cassandra almost daily for my job. A lot of our services require this high performance, highly available database. The command line tool cqlsh is the official tool for interacting with Cassandra. cqlsh is an easy and intuitive terminal into Apache Cassandra, but it has dependencies, one of which is Python. Over the years of local development on my MacBook Pro, I have had many tools that require Python and Python libraries. Some of these tools I installed years ago require older versions of Python, or older Python libraries not able to run in newer Python versions. Python is a great language, but sooner or later you run into dependency nightmares, (see The Nine Circles of Python Dependency Hell) including missing libs, version conflicts, and the list goes on. It makes sense to resolve these issues or use a Python version manager like Ruby’s RVM if you are actively developing locally in Python. But wait, I’m not developing in Python at the moment, I just want to run cqlsh, and it is not the weekend, so I am not motivated to Google my Python version conflicts and library dependency errors because I have a ton of work to get done. Yes, my problems, likely caused by something dumb I did playing around with the questionable code I found in the far-off corners of Github.
So I’m going to ignore my confused local install of cqlsh, the broken state of my Python and the mess I made of its libraries. I’m just going to run:
docker run -it --rm cassandra cqlsh node1.example.com -u itsme -p mypassword`
It’s a one time pull of the Cassandra Docker image and once done the --rm flag cleans up the stopped container.
But that’s a lot of command for me to think about when I just need my cqlsh so I add a simple alias to my .bashrc
alias cqlsh='docker run -it --rm cassandra cqlsh`
From now on I run the command cqlsh and get just that, will all its dependencies in isolation, not worried about Python versions or state of my local workstation. Just keep Docker running well, and I’m good.
The alias above is helpful for the times I just want a cqlsh terminal to issue a few commands. However, I often need to pass cql scripts into cqlsh. So I updated my alias to always mount my current directory into a /src directory in the container. All I have have to remember is that that path to a local file is ./src and not ./.
alias cqlsh='docker run -it --rm -v "$(pwd)":/src cassandra cqlsh
This allows me to run commands that pass in files, like:
$ cqlsh node1.example.com 9042 -f /src/setup_some_keyspace_and_tables.cql
The Cassandra Docker image is 323MB, and when run without a command will start up a fully functional Cassandra node, which is useful for testing. However, if this is not something you need, then a 323MB image is a bit overkill. You can always make a small Docker image using [Alpine Linux], adding only the packages you need. However, that is a subject of another article I suppose.
Advanced Platform Development with Kubernetes
What You'll Learn
- Build data pipelines with MQTT, NiFi, Logstash, MinIO, Hive, Presto, Kafka and Elasticsearch
- Leverage Serverless ETL with OpenFaaS
- Explore Blockchain networking with Ethereum
- Support a multi-tenant Data Science platform with JupyterHub, MLflow and Seldon Core
- Build a Multi-cloud, Hybrid cluster, securely bridging on-premise and cloud-based Kubernetes nodes
This blog post, titled: "Don't Install cqlsh: Containers as utility applications" by Craig Johnston, is licensed under a Creative Commons Attribution 4.0 International License.
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