CKA 备考 - 5 - 为应用注入环境变量

通过分析实操题来学习、巩固cka中的考点。本次的重点是发布应用时为应用注入环境变量。

题目

使用 busybox 最新版本的镜像建立一个 pod, 并运行 sleep 命令，间隔为1小时，并为该pod配置一个环境变量，变量名为：PLANET, 值为: blue

解题思路

核心概念

1. run 命令

在 kubernetes 集群中，可以使用run命令直接部署一个pod，但这样的pod是不能通过ReplicaSet进行扩展，更糟糕的是Pod不具有自愈性。生产环境不建议直接用run命令。

2. 为Pod指定环境变量

创建 Pod 时，可以为其下的容器设置环境变量。通过配置文件的 env 或者 envFrom 字段来设置环境变量。

相关命令

1. kubectl run 命令

通过 kubectl run –help 可以获得如下的帮助信息:

Create and run a particular image in a pod.

Examples:
  # Start a nginx pod
  kubectl run nginx --image=nginx
  
  # Start a hazelcast pod and let the container expose port 5701
  kubectl run hazelcast --image=hazelcast/hazelcast --port=5701
  
  # Start a hazelcast pod and set environment variables "DNS_DOMAIN=cluster" and "POD_NAMESPACE=default" in the
container
  kubectl run hazelcast --image=hazelcast/hazelcast --env="DNS_DOMAIN=cluster" --env="POD_NAMESPACE=default"
  
  # Start a hazelcast pod and set labels "app=hazelcast" and "env=prod" in the container
  kubectl run hazelcast --image=hazelcast/hazelcast --labels="app=hazelcast,env=prod"
  
  # Dry run; print the corresponding API objects without creating them
  kubectl run nginx --image=nginx --dry-run=client
  
  # Start a nginx pod, but overload the spec with a partial set of values parsed from JSON
  kubectl run nginx --image=nginx --overrides='{ "apiVersion": "v1", "spec": { ... } }'
  
  # Start a busybox pod and keep it in the foreground, don't restart it if it exits
  kubectl run -i -t busybox --image=busybox --restart=Never
  
  # Start the nginx pod using the default command, but use custom arguments (arg1 .. argN) for that command
  kubectl run nginx --image=nginx -- <arg1> <arg2> ... <argN>
  
  # Start the nginx pod using a different command and custom arguments
  kubectl run nginx --image=nginx --command -- <cmd> <arg1> ... <argN>

Options:
      --allow-missing-template-keys=true: If true, ignore any errors in templates when a field or map key is missing in
the template. Only applies to golang and jsonpath output formats.
      --annotations=[]: Annotations to apply to the pod.
      --attach=false: If true, wait for the Pod to start running, and then attach to the Pod as if 'kubectl attach ...'
were called.  Default false, unless '-i/--stdin' is set, in which case the default is true. With '--restart=Never' the
exit code of the container process is returned.
      --cascade='background': Must be "background", "orphan", or "foreground". Selects the deletion cascading strategy
for the dependents (e.g. Pods created by a ReplicationController). Defaults to background.
      --command=false: If true and extra arguments are present, use them as the 'command' field in the container, rather
than the 'args' field which is the default.
      --dry-run='none': Must be "none", "server", or "client". If client strategy, only print the object that would be
sent, without sending it. If server strategy, submit server-side request without persisting the resource.
      --env=[]: Environment variables to set in the container.
      --expose=false: If true, service is created for the container(s) which are run
      --field-manager='kubectl-run': Name of the manager used to track field ownership.
  -f, --filename=[]: to use to replace the resource.
      --force=false: If true, immediately remove resources from API and bypass graceful deletion. Note that immediate
deletion of some resources may result in inconsistency or data loss and requires confirmation.
      --grace-period=-1: Period of time in seconds given to the resource to terminate gracefully. Ignored if negative.
Set to 1 for immediate shutdown. Can only be set to 0 when --force is true (force deletion).
      --image='': The image for the container to run.
      --image-pull-policy='': The image pull policy for the container. If left empty, this value will not be specified
by the client and defaulted by the server
  -k, --kustomize='': Process a kustomization directory. This flag can't be used together with -f or -R.
  -l, --labels='': Comma separated labels to apply to the pod(s). Will override previous values.
      --leave-stdin-open=false: If the pod is started in interactive mode or with stdin, leave stdin open after the
first attach completes. By default, stdin will be closed after the first attach completes.
  -o, --output='': Output format. One of:
json|yaml|name|go-template|go-template-file|template|templatefile|jsonpath|jsonpath-as-json|jsonpath-file.
      --overrides='': An inline JSON override for the generated object. If this is non-empty, it is used to override the
generated object. Requires that the object supply a valid apiVersion field.
      --pod-running-timeout=1m0s: The length of time (like 5s, 2m, or 3h, higher than zero) to wait until at least one
pod is running
      --port='': The port that this container exposes.
      --privileged=false: If true, run the container in privileged mode.
  -q, --quiet=false: If true, suppress prompt messages.
  -R, --recursive=false: Process the directory used in -f, --filename recursively. Useful when you want to manage
related manifests organized within the same directory.
      --restart='Always': The restart policy for this Pod.  Legal values [Always, OnFailure, Never].
      --rm=false: If true, delete resources created in this command for attached containers.
      --save-config=false: If true, the configuration of current object will be saved in its annotation. Otherwise, the
annotation will be unchanged. This flag is useful when you want to perform kubectl apply on this object in the future.
      --show-managed-fields=false: If true, keep the managedFields when printing objects in JSON or YAML format.
  -i, --stdin=false: Keep stdin open on the container(s) in the pod, even if nothing is attached.
      --template='': Template string or path to template file to use when -o=go-template, -o=go-template-file. The
template format is golang templates [http://golang.org/pkg/text/template/#pkg-overview].
      --timeout=0s: The length of time to wait before giving up on a delete, zero means determine a timeout from the
size of the object
  -t, --tty=false: Allocated a TTY for each container in the pod.
      --wait=false: If true, wait for resources to be gone before returning. This waits for finalizers.

Usage:
  kubectl run NAME --image=image [--env="key=value"] [--port=port] [--dry-run=server|client] [--overrides=inline-json]
[--command] -- [COMMAND] [args...] [options]

Use "kubectl options" for a list of global command-line options (applies to all commands).

解题步骤

方法1

直接执行以下命令

kubectl run envvar --image=busybox:latest --env="PLANET=blue"  --command -- sleep "3600"

注意: “–command” 一定要放在最后，否则后面的参数有可能会被当成命令的参数来处理，比如这样写: –command – sleep “3600” –env=”PLANET=blue” 的结果就是错误的

方法2

首先使用 –dry-run 选项生成一个指令文件：envvar.yml

kubectl run envvar --image=busybox:latest --dry-run=client -o yaml > envvar.yml

编辑 envvar.yml 文件, 以运行 sleep 及加入环境变量

apiVersion: v1
kind: Pod
metadata:
  labels:
    run: envvar
  name: envvar
spec:
  containers:
  - image: busybox:latest
    name: envvar
    args:
      - sleep
      - "3600"
    env:
      - name: PLANET
        value: "blue"

然后运行

运行

kubectl apply -f envvar.yml

验证结果

kubectl exec envvar -- env | grep PLANET