Kubernetes中YAML文件编写
1、YAML格式基本规范
YAML（YAML Ain't Markup Language）是一种用于数据序列化的格式，常用于配置文件、数据交换等场景。YAML的目标是易于阅读和书写，同时也易于与编程语言交互。YAML文件通常以.yaml或.yml作为文件扩展名。
YAML格式基本规范：
结构表示：
- 使用缩进表示层级关系，通常使用两个或四个空格的缩进，但必须在同一文档中保持一致。
- 不使用制表符（Tab）进行缩进。
键值对：
- 使用冒号加空格: 来分隔键和值。
- 键是唯一的，通常是字符串。
列表（数组）：
- 使用短横线加空格- 来表示列表项。
- 列表项通常会缩进，表示属于上一级的列表。
字典（映射）：
- 字典是一组键值对的集合。
- 字典的每个键值对都会缩进，表示属于上一级的字典。
数据类型：
- 支持字符串、布尔值、整数、浮点数、null、时间、日期等数据类型。
- 字符串通常不需要引号，但如果包含特殊字符，则需要用单引号或双引号括起来。
- 使用true/false表示布尔值。
- 使用null表示空值。
注释：
- 使用井号 # 开头表示注释，注释内容不会被解析。
多文档支持：
- 使用三个短横线---来分隔文件中的多个文档。
复杂结构：
- 字典和列表可以嵌套使用，形成复杂的结构。
这是一个简单的YAML示例，展示了一些基本的格式：
# 这是一个注释
person: # 字典的开始
name: John Doe # 字符串
age: 30 # 整数
married: true # 布尔值
children: # 列表的开始
- name: Jane Doe
age: 10
- name: Doe Junior
age: 5
# 它对应的JSON文件如下：
{
"person": {
"name": "John Doe",
"age": 30,
"married": true,
"children": [
{
"name": "Jane Doe",
"age": 10
},
{
"name": "Doe Junior",
"age": 5
}
]
}
}
2、K8S中YAML文件编写
YAML文件通常用于配置管理系统、部署工具、持续集成和持续部署（CI/CD）等场景，它们易于阅读和编辑。在Kubernetes中，YAML文件被广泛用于定义资源对象，如Deployments、Services、Pods等。
通过定义Deployment资源对象的过程，看下YAML文件编写的思路。
YAML文件的组成
YAML文件由apiVersion、kind、metadata、spec、status五部分组成，前四部分较常用。
root@k8s-master01:~# kubectl explain deployment
KIND: Deployment
VERSION: apps/v1
DESCRIPTION:
Deployment enables declarative updates for Pods and ReplicaSets.
FIELDS:
apiVersion <string>
APIVersion defines the versioned schema of this representation of an
object. Servers should convert recognized schemas to the latest internal
value, and may reject unrecognized values. More info:
https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources
kind <string>
Kind is a string value representing the REST resource this object
represents. Servers may infer this from the endpoint the client submits
requests to. Cannot be updated. In CamelCase. More info:
https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds
metadata <Object>
Standard object's metadata. More info:
https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
spec <Object>
Specification of the desired behavior of the Deployment.
status <Object>
Most recently observed status of the Deployment.
--dry-run生成YAML文件框架
通过--dry-run生成YAML文件框架
root@k8s-master01:~# kubectl create deployment jumpoint-web --image=nginx:latest --port=80 --replicas=2 --namespace=jumpoint-ns --dry-run=client --output=yaml
apiVersion: apps/v1
kind: Deployment
metadata:
creationTimestamp: null
labels:
app: jumpoint-web
name: jumpoint-web
namespace: jumpoint-ns
spec:
replicas: 2
selector:
matchLabels:
app: jumpoint-web
strategy: {}
template:
metadata:
creationTimestamp: null
labels:
app: jumpoint-web
spec:
containers:
- image: nginx:latest
name: nginx
ports:
- containerPort: 80
resources: {}
status: {}
通过explain获取YAML文件字段含义
# 若要查看metadata.labels字段的含义：
root@k8s-master01:~# kubectl explain deployment.metadata.labels
KIND: Deployment
VERSION: apps/v1
FIELD: labels <map[string]string>
DESCRIPTION:
Map of string keys and values that can be used to organize and categorize
(scope and select) objects. May match selectors of replication controllers
and services. More info: http://kubernetes.io/docs/user-guide/labels
# 若要查看deployment.spec.template.spec.containers字段下还有哪些字段可用
root@k8s-master01:~# kubectl explain deployment.spec.template.spec.containers
KIND: Deployment
VERSION: apps/v1
RESOURCE: containers <[]Object>
DESCRIPTION:
List of containers belonging to the pod. Containers cannot currently be
added or removed. There must be at least one container in a Pod. Cannot be
updated.
A single application container that you want to run within a pod.
FIELDS:
...
imagePullPolicy <string>
Image pull policy. One of Always, Never, IfNotPresent. Defaults to Always
if :latest tag is specified, or IfNotPresent otherwise. Cannot be updated.
More info:
https://kubernetes.io/docs/concepts/containers/images#updating-images
Possible enum values:
- `"Always"` means that kubelet always attempts to pull the latest image.
Container will fail If the pull fails.
- `"IfNotPresent"` means that kubelet pulls if the image isn't present on
disk. Container will fail if the image isn't present and the pull fails.
- `"Never"` means that kubelet never pulls an image, but only uses a local
image. Container will fail if the image isn't present
...
调整YAML文件内容
精简不用的字段、修改字段的内容、添加镜像的拉取策略等，将其保存到nginx-deployment.yaml文件中。
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: jumpoint-web-deployment-label
name: jumpoint-web
namespace: jumpoint-ns
spec:
replicas: 2
selector:
matchLabels:
app: jumpoint-web-pod-label
template:
metadata:
labels:
app: jumpoint-web-pod-label
spec:
containers:
- image: nginx:latest
name: jumpoint-web-container-name
imagePullPolicy: Always
ports:
- containerPort: 80
protocol: TCP
name: http
使用nginx-deployment.yaml文件创建Deployment资源对象。
root@k8s-master01:~/yaml-resources# kubectl create namespace jumpoint-ns
namespace/jumpoint-ns created
root@k8s-master01:~/yaml-resources# kubectl apply -f nginx-deployment.yaml
deployment.apps/jumpoint-web created
root@k8s-master01:~/yaml-resources# kubectl get deployments -n jumpoint-ns
NAME READY UP-TO-DATE AVAILABLE AGE
jumpoint-web 2/2 2 2 95s
root@k8s-master01:~/yaml-resources# kubectl get pods -n jumpoint-ns -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
jumpoint-web-66c66b4db4-f5dw4 1/1 Running 0 3m49s 10.200.2.14 k8s-node02-237 <none> <none>
jumpoint-web-66c66b4db4-x8jqj 1/1 Running 0 3m49s 10.200.1.13 k8s-node01-236 <none> <none>
root@k8s-master01-235:~/yaml-resources# kubectl describe deployment -n jumpoint-ns jumpoint-web
Name: jumpoint-web
Namespace: jumpoint-ns
CreationTimestamp: Tue, 30 Apr 2024 13:13:50 +0800
Labels: app=jumpoint-web-deployment-label
Annotations: deployment.kubernetes.io/revision: 1
Selector: app=jumpoint-web-pod-label
Replicas: 2 desired | 2 updated | 2 total | 2 available | 0 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 25% max unavailable, 25% max surge
Pod Template:
Labels: app=jumpoint-web-pod-label
Containers:
jumpoint-web-container-name:
Image: nginx:latest
Port: 80/TCP
Host Port: 0/TCP
Environment: <none>
Mounts: <none>
Volumes: <none>
Conditions:
Type Status Reason
---- ------ ------
Available True MinimumReplicasAvailable
Progressing True NewReplicaSetAvailable
OldReplicaSets: <none>
NewReplicaSet: jumpoint-web-66c66b4db4 (2/2 replicas created)
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal ScalingReplicaSet 3m19s deployment-controller Scaled up replica set jumpoint-web-66c66b4db4 to 2