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MongoDB Container data loss issue – A Journey

Recently updated on November 3rd, 2021 at 10:49 am

Over the past month or so I noticed an issue with my Pac-Man Kubernetes application, which I use for demonstrations as a basic app front-end that writes to a database back end, running in Kubernetes.

  • When I restored my instances using Kasten, my Pac-Man high scores were missing.
  • This issue happened when I made some changes to my deployment files to configure authentication to the MongoDB using environment variables in my deployment file.

This blog post is a detail walk-through of the steps I took to troubleshoot the issue, and then rectify it!

Summary if you don’t want to read the post

If you are not looking to read through this blog post, here is the summary:

  • I changed MongoDB images, I needed to configure a new mount point location to match the MongoDB configuration
  • New MongoDB image is non-root, so had to use an Init container to configure the permissions on the PV first
Overview of the application

The application is made up of the following components:

  • Namespace
  • Deployment
    • MongoDB Pod
      • DB Authentication configured
      • Attached to a PVC
    • Pac-Man Pod
      • Nodejs web front end that connects back to the MongoDB Pod by looking for the Pod DNS address internally.
  • RBAC Configuration for Pod Security and Service Account
  • Secret which holds the data for the MongoDB Usernames and Passwords to be configured
  • Service
    • Type: LoadBalancer
      • Used to balance traffic to the Pac-Man Pods

Pac-Man Kubernetes Diagram

Confirming the behaviour

The behaviour I was seeing when my application was deployed:

  • Pac-Man web page – I could save a high score, and it would show in the high scores list
    • This showed the connectivity to the database was working, as the app would hang if it could not write to the database.
  • I would protect my application using Kasten. When I deleted the namespace, and restored everything, my application would be running, but there was no high scores to show.
  • This was apparent from deploying the branch version v0.5.0 and v0.5.1 from my GitHub.
  • Deploying the branch v0.2.0 would not product the same behaviour
    • This configuration did not have any database authentication setup, meaning MongoDB was open to the world if they could connect without a UN/Password.
Testing the Behaviour

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