File system

As explained in Kubernetes in Action, Second Edition

A filesystem is a structure and set of operations for organizing, storing, and accessing files, including the isolated filesystem presented to a container.

A filesystem organizes, stores, and exposes files through operations such as reading and writing. In containers, each container starts with an isolated filesystem derived from its image. Mounting attaches another volume or storage filesystem at a location in that file tree. section 9.1 section 2.1.2

Container filesystems have several operational distinctions:

• Image files are present when a container starts, but changes made inside the container disappear when it is replaced after termination. section 9.1
• A volume preserves all or part of an application filesystem across container restarts when mounted into the pod and container. section 9.1
• Containers in one pod still have separate mount namespaces; mounting the same volume into both lets them share selected files. section 5.1.1
• A hostPath volume exposes a path from the node filesystem, such as /run/xtables.lock or /lib/modules, to a pod container. section 17.2.2

A node filesystem exposed through hostPath

A kube-proxy DaemonSet uses hostPath volumes to access the node’s /run/xtables.lock file and /lib/modules directory. This enables a per-node process to use host networking-related files and installed kernel modules. section 17.2.2

Figure 9.1 Mounting a filesystem into the file tree

Use the filesystem-mounting diagram to see how a volume becomes available at a location inside a container’s file tree. section 9.1

How Kubernetes in Action, Second Edition covers it

How deep it goes

Defines isolation, mounting, persistence, and mount namespaces, then demonstrates hostPath usage without detailing filesystem implementation internals.

Examples

Uses container restarts, shared pod volumes, and kube-proxy hostPath mounts for /run/xtables.lock and /lib/modules.

What it assumes

Assumes basic containers and pods while teaching isolated filesystems, mounting, persistence, and shared volume behavior.

What you can do after

Operate/configure container storage by mounting volumes for persistence or sharing and exposing node paths through hostPath.

How it connects

Connects filesystems with container images, containers, pods, volumes, mount namespaces, DaemonSets, and hostPath volumes.

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Also explained in

• 

  liveBookmanning.com
  Amazon Web Services in Action, Third Edition: An in-depth guide to AWSA filesystem is a data-management structure that organizes blocks into files and directories for operating-system access.
• 

  liveBookmanning.com
  Bootstrapping Microservices, Second Edition: With Docker, Kubernetes, GitHub Actions, and TerraformFile storage is a persistent storage mechanism that organizes data as files.
• 

  liveBookmanning.com
  100 Java Mistakes and How to Avoid ThemA filesystem is a system that organizes and provides access to files and directories on storage or through a mounted hierarchy.

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Related concepts

• copy instructionused by · The Dockerfile COPY instruction copies files or directories from a build context or another build stage into an image’s filesystem.
• bind mountused by · A bind mount makes an existing file or directory accessible at another filesystem location, commonly exposing host contents within a container.
• monitoringused by · Monitoring is the ongoing observation and measurement of a system’s behavior, state, or operational signals to assess its condition and detect changes or problems.
• container securityaddressed by · Container security is the practice of protecting container images, runtimes, workloads, hosts, configurations, and supporting infrastructure from vulnerabilities, compromise, and unauthorized activity.
• WASIused by · WASI, the WebAssembly System Interface, is a standardized collection of interfaces that enables WebAssembly programs to access operating-system-like resources portably.

This explainer was generated by Manning's knowledge graph from the text of Kubernetes in Action, Second Edition. The section links point to the parts of the book it draws on.