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Container prerequisites for Kubernetes

Before deploying applications to Kubernetes, workloads must be containerized using a runtime such as Docker.^[400-devops__06-Kubernetes__basics__README.md] This process requires adherence to specific architectural assumptions to ensure applications can be successfully scheduled and managed within the cluster.^[400-devops__06-Kubernetes__basics__README.md]

Core Container Assumptions

To function correctly within a Kubernetes environment, a container image and its configuration must meet the following requirements:

  • Definition: The application must be defined via a container definition file, such as a Dockerfile.^[400-devops__06-Kubernetes__basics__README.md]
  • Traffic Exposure: The application must serve traffic by exposing specific ports.^[400-devops__06-Kubernetes__basics__README.md]
  • Configuration Management: Configuration data and secrets must be handled via mounted files, secrets, or environment variables.^[400-devops__06-Kubernetes__basics__README.md]
  • Data Persistence: The container must be designed with the understanding that internal storage is ephemeral; when a container terminates, its internal state is lost.^[400-devops__06-Kubernetes__basics__README.md]
  • Entrypoint: The container requires a defined main process (the application) to run as the entrypoint.^[400-devops__06-Kubernetes__basics__README.md]

Managing State and Ephemeral Nature

A critical prerequisite for stateful applications, such as databases, is understanding that containers are ephemeral by default.^[400-devops__06-Kubernetes__basics__README.md] Just as software installed on a server stores files in specific directories, containerized stateful applications require external storage mechanisms to persist data beyond the lifecycle of the container.^[400-devops__06-Kubernetes__basics__README.md]

Sources

  • 400-devops__06-Kubernetes__basics__README.md