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A Practical Guide to Kubernetes

Defining Pods through Declarative Syntax

Explore how to define Kubernetes Pods using declarative YAML syntax. Understand the key components such as apiVersion, metadata, and spec for containers. Learn to create, view, and describe Pods to effectively manage containerized applications in a cluster environment.

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Pods as wrappers for containers

Even though a Pod can contain any number of containers, the most common use case is to use the single-container-in-a-Pod model. In such a case, a Pod is a wrapper around one container. From Kubernetes’ perspective, a Pod is the smallest unit. We cannot tell Kubernetes to run a container. Instead, we ask it to create a Pod that wraps around a container.

Looking into a Pod’s definition

Let’s look at a simple Pod db.yml definition:

YAML
apiVersion: v1
kind: Pod
metadata:
  name: db
  labels:
    type: db
    vendor: MongoLabs
spec:
  containers:
  - name: db
    image: mongo:3.3
    command: ["mongod"]
    args: ["--rest", "--httpinterface"]

Let’s analyze the various sections in the output definition of a Pod:

  • Lines 1–2: We use v1 of Kubernetes Pods API. Both apiVersion and kind are mandatory. That way, Kubernetes knows what we want to do (create a Pod) and which API version to use.

  • Lines 3–7: The next ...