k8s学习-k8s资源对象与yaml结构

简介: k8s学习-k8s资源对象与yaml结构

资源对象

概念

Kubernetes对象是持久化的实体。 Kubernetes使用这些实体去表示整个集群的状态。Kubernetes 对象是“目标性记录”——一旦创建对象,Kubernetes系统将不断工作以确保对象存在

对象规约(spec)

期望的状态

你必须在创建对象时设置其内容,描述你希望对象所具有的特征

状态(status)

当前观测到的状态

由 Kubernetes 系统和组件设置并更新的。 在任何时刻,Kubernetes 控制平面 都一直都在积极地管理着对象的实际状态,以使之达成期望状态

yaml

模板

模板可以使用run命令生成,或者使用get命令获取已有的资源对象的json或yaml文件。

命令

kubectl run nginx-test --image=nginx --port=80 --replicas=3 --dry-run -o yaml > nginx-test.yaml

截图

yaml内容

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx-test
  name: nginx-test
spec:
  containers:
  - image: nginx
    name: nginx-test
    ports:
    - containerPort: 80
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}

可以看到,一个对象的yaml文件,一般包含apiVersion、Kind、metadata、spec和status(非必须)。

api version

运行以下命令就能看到当前k8s支持的api版本,你的可能和博主不一样哈

命令

kubectl api-versions

截图

文字版

admissionregistration.k8s.io/v1
admissionregistration.k8s.io/v1beta1
apiextensions.k8s.io/v1
apiextensions.k8s.io/v1beta1
apiregistration.k8s.io/v1
apiregistration.k8s.io/v1beta1
apps/v1
authentication.k8s.io/v1
authentication.k8s.io/v1beta1
authorization.k8s.io/v1
authorization.k8s.io/v1beta1
autoscaling/v1
autoscaling/v2beta1
autoscaling/v2beta2
batch/v1
batch/v1beta1
certificates.k8s.io/v1beta1
coordination.k8s.io/v1
coordination.k8s.io/v1beta1
crd.projectcalico.org/v1
discovery.k8s.io/v1beta1
events.k8s.io/v1beta1
extensions/v1beta1
networking.k8s.io/v1
networking.k8s.io/v1beta1
node.k8s.io/v1beta1
policy/v1beta1
rbac.authorization.k8s.io/v1
rbac.authorization.k8s.io/v1beta1
scheduling.k8s.io/v1
scheduling.k8s.io/v1beta1
storage.k8s.io/v1
storage.k8s.io/v1beta1
v1

Kind

Kind分为三类:

  • 对象代表系统中的持久实体。例如,Pod, ReplicationController, Service, Namespace等。
  • 列表是一种(通常)或多种(偶尔)类型的资源的集合。例如,PodList, ServiceList,等。
  • 简单种类用于对象上的特定操作和非持久实体。

具体支持哪些,可以查看k8s学习-kubectl命令常用选项详解与实战的资源类型一部分。

metadata

所有字段

metadata的所有字段如下:

annotations  <map[string]string>
     Annotations is an unstructured key value map stored with a resource that
     may be set by external tools to store and retrieve arbitrary metadata. They
     are not queryable and should be preserved when modifying objects. More
     info: http://kubernetes.io/docs/user-guide/annotations
   clusterName  <string>
     The name of the cluster which the object belongs to. This is used to
     distinguish resources with same name and namespace in different clusters.
     This field is not set anywhere right now and apiserver is going to ignore
     it if set in create or update request.
   creationTimestamp    <string>
     CreationTimestamp is a timestamp representing the server time when this
     object was created. It is not guaranteed to be set in happens-before order
     across separate operations. Clients may not set this value. It is
     represented in RFC3339 form and is in UTC. Populated by the system.
     Read-only. Null for lists. More info:
     https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
   deletionGracePeriodSeconds   <integer>
     Number of seconds allowed for this object to gracefully terminate before it
     will be removed from the system. Only set when deletionTimestamp is also
     set. May only be shortened. Read-only.
   deletionTimestamp    <string>
     DeletionTimestamp is RFC 3339 date and time at which this resource will be
     deleted. This field is set by the server when a graceful deletion is
     requested by the user, and is not directly settable by a client. The
     resource is expected to be deleted (no longer visible from resource lists,
     and not reachable by name) after the time in this field, once the
     finalizers list is empty. As long as the finalizers list contains items,
     deletion is blocked. Once the deletionTimestamp is set, this value may not
     be unset or be set further into the future, although it may be shortened or
     the resource may be deleted prior to this time. For example, a user may
     request that a pod is deleted in 30 seconds. The Kubelet will react by
     sending a graceful termination signal to the containers in the pod. After
     that 30 seconds, the Kubelet will send a hard termination signal (SIGKILL)
     to the container and after cleanup, remove the pod from the API. In the
     presence of network partitions, this object may still exist after this
     timestamp, until an administrator or automated process can determine the
     resource is fully terminated. If not set, graceful deletion of the object
     has not been requested. Populated by the system when a graceful deletion is
     requested. Read-only. More info:
     https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
   finalizers   <[]string>
     Must be empty before the object is deleted from the registry. Each entry is
     an identifier for the responsible component that will remove the entry from
     the list. If the deletionTimestamp of the object is non-nil, entries in
     this list can only be removed. Finalizers may be processed and removed in
     any order. Order is NOT enforced because it introduces significant risk of
     stuck finalizers. finalizers is a shared field, any actor with permission
     can reorder it. If the finalizer list is processed in order, then this can
     lead to a situation in which the component responsible for the first
     finalizer in the list is waiting for a signal (field value, external
     system, or other) produced by a component responsible for a finalizer later
     in the list, resulting in a deadlock. Without enforced ordering finalizers
     are free to order amongst themselves and are not vulnerable to ordering
     changes in the list.
   generateName <string>
     GenerateName is an optional prefix, used by the server, to generate a
     unique name ONLY IF the Name field has not been provided. If this field is
     used, the name returned to the client will be different than the name
     passed. This value will also be combined with a unique suffix. The provided
     value has the same validation rules as the Name field, and may be truncated
     by the length of the suffix required to make the value unique on the
     server. If this field is specified and the generated name exists, the
     server will NOT return a 409 - instead, it will either return 201 Created
     or 500 with Reason ServerTimeout indicating a unique name could not be
     found in the time allotted, and the client should retry (optionally after
     the time indicated in the Retry-After header). Applied only if Name is not
     specified. More info:
     https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#idempotency
   generation   <integer>
     A sequence number representing a specific generation of the desired state.
     Populated by the system. Read-only.
   labels       <map[string]string>
     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
   managedFields        <[]Object>
     ManagedFields maps workflow-id and version to the set of fields that are
     managed by that workflow. This is mostly for internal housekeeping, and
     users typically shouldn't need to set or understand this field. A workflow
     can be the user's name, a controller's name, or the name of a specific
     apply path like "ci-cd". The set of fields is always in the version that
     the workflow used when modifying the object.
   name <string>
     Name must be unique within a namespace. Is required when creating
     resources, although some resources may allow a client to request the
     generation of an appropriate name automatically. Name is primarily intended
     for creation idempotence and configuration definition. Cannot be updated.
     More info: http://kubernetes.io/docs/user-guide/identifiers#names
   namespace    <string>
     Namespace defines the space within each name must be unique. An empty
     namespace is equivalent to the "default" namespace, but "default" is the
     canonical representation. Not all objects are required to be scoped to a
     namespace - the value of this field for those objects will be empty. Must
     be a DNS_LABEL. Cannot be updated. More info:
     http://kubernetes.io/docs/user-guide/namespaces
   ownerReferences      <[]Object>
     List of objects depended by this object. If ALL objects in the list have
     been deleted, this object will be garbage collected. If this object is
     managed by a controller, then an entry in this list will point to this
     controller, with the controller field set to true. There cannot be more
     than one managing controller.
   resourceVersion      <string>
     An opaque value that represents the internal version of this object that
     can be used by clients to determine when objects have changed. May be used
     for optimistic concurrency, change detection, and the watch operation on a
     resource or set of resources. Clients must treat these values as opaque and
     passed unmodified back to the server. They may only be valid for a
     particular resource or set of resources. Populated by the system.
     Read-only. Value must be treated as opaque by clients and . More info:
     https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#concurrency-control-and-consistency
   selfLink     <string>
     SelfLink is a URL representing this object. Populated by the system.
     Read-only. DEPRECATED Kubernetes will stop propagating this field in 1.20
     release and the field is planned to be removed in 1.21 release.
   uid  <string>
     UID is the unique in time and space value for this object. It is typically
     generated by the server on successful creation of a resource and is not
     allowed to change on PUT operations. Populated by the system. Read-only.
     More info: http://kubernetes.io/docs/user-guide/identifiers#uids

常用的有以下几个:

  • annotaions:注解。
  • clusterName:集群名称。
  • labels:标签。
  • name:名称(namespace中唯一)。
  • namespace:命名空间(大部分情况下使用kubectl中的-n指定,不写到yaml中)。
  • ownerReferences:依赖于这个对象的其他对象。
  • uid:唯一字符串。

这里再介绍下常用的label、annotations。

labels

标签(Labels) 是附加到 Kubernetes 对象(比如 Pods)上的键值对。 标签旨在用于指定对用户有意义且相关的对象的标识属性,但不直接对核心系统有语义含义。 标签可以用于组织和选择对象的子集。标签可以在创建时附加到对象,随后可以随时添加和修改。 每个对象都可以定义一组键/值标签。每个键对于给定对象必须是唯一的。

可以使用-l进行筛选:

命令

kubectl get po -n killer -l app=nginx

截图

annotations

你可以使用 Kubernetes 注解(Annotations)为对象附加任意的非标识的元数据。客户端程序(例如工具和库)能够获取这些元数据信息。

特点如下:

  • 一般比label大
  • 可以包含特殊字符
  • 可以结构化也可以非结构化

帮助

如果yaml中的某个关键字不懂,可以使用explain命令进行详细解释。

命令

kubectl explain pods.spec.containers

结果

containers全部内容

KIND:     Pod
VERSION:  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:
   args <[]string>
     Arguments to the entrypoint. The docker image's CMD is used if this is not
     provided. Variable references $(VAR_NAME) are expanded using the
     container's environment. If a variable cannot be resolved, the reference in
     the input string will be unchanged. The $(VAR_NAME) syntax can be escaped
     with a double $$, ie: $$(VAR_NAME). Escaped references will never be
     expanded, regardless of whether the variable exists or not. Cannot be
     updated. More info:
     https://kubernetes.io/docs/tasks/inject-data-application/define-command-argument-container/#running-a-command-in-a-shell
   command      <[]string>
     Entrypoint array. Not executed within a shell. The docker image's
     ENTRYPOINT is used if this is not provided. Variable references $(VAR_NAME)
     are expanded using the container's environment. If a variable cannot be
     resolved, the reference in the input string will be unchanged. The
     $(VAR_NAME) syntax can be escaped with a double $$, ie: $$(VAR_NAME).
     Escaped references will never be expanded, regardless of whether the
     variable exists or not. Cannot be updated. More info:
     https://kubernetes.io/docs/tasks/inject-data-application/define-command-argument-container/#running-a-command-in-a-shell
   env  <[]Object>
     List of environment variables to set in the container. Cannot be updated.
   envFrom      <[]Object>
     List of sources to populate environment variables in the container. The
     keys defined within a source must be a C_IDENTIFIER. All invalid keys will
     be reported as an event when the container is starting. When a key exists
     in multiple sources, the value associated with the last source will take
     precedence. Values defined by an Env with a duplicate key will take
     precedence. Cannot be updated.
   image        <string>
     Docker image name. More info:
     https://kubernetes.io/docs/concepts/containers/images This field is
     optional to allow higher level config management to default or override
     container images in workload controllers like Deployments and StatefulSets.
   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
   lifecycle    <Object>
     Actions that the management system should take in response to container
     lifecycle events. Cannot be updated.
   livenessProbe        <Object>
     Periodic probe of container liveness. Container will be restarted if the
     probe fails. Cannot be updated. More info:
     https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle#container-probes
   name <string> -required-
     Name of the container specified as a DNS_LABEL. Each container in a pod
     must have a unique name (DNS_LABEL). Cannot be updated.
   ports        <[]Object>
     List of ports to expose from the container. Exposing a port here gives the
     system additional information about the network connections a container
     uses, but is primarily informational. Not specifying a port here DOES NOT
     prevent that port from being exposed. Any port which is listening on the
     default "0.0.0.0" address inside a container will be accessible from the
     network. Cannot be updated.
   readinessProbe       <Object>
     Periodic probe of container service readiness. Container will be removed
     from service endpoints if the probe fails. Cannot be updated. More info:
     https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle#container-probes
   resources    <Object>
     Compute Resources required by this container. Cannot be updated. More info:
     https://kubernetes.io/docs/concepts/configuration/manage-compute-resources-container/
   securityContext      <Object>
     Security options the pod should run with. More info:
     https://kubernetes.io/docs/concepts/policy/security-context/ More info:
     https://kubernetes.io/docs/tasks/configure-pod-container/security-context/
   startupProbe <Object>
     StartupProbe indicates that the Pod has successfully initialized. If
     specified, no other probes are executed until this completes successfully.
     If this probe fails, the Pod will be restarted, just as if the
     livenessProbe failed. This can be used to provide different probe
     parameters at the beginning of a Pod's lifecycle, when it might take a long
     time to load data or warm a cache, than during steady-state operation. This
     cannot be updated. This is an alpha feature enabled by the StartupProbe
     feature flag. More info:
     https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle#container-probes
   stdin        <boolean>
     Whether this container should allocate a buffer for stdin in the container
     runtime. If this is not set, reads from stdin in the container will always
     result in EOF. Default is false.
   stdinOnce    <boolean>
     Whether the container runtime should close the stdin channel after it has
     been opened by a single attach. When stdin is true the stdin stream will
     remain open across multiple attach sessions. If stdinOnce is set to true,
     stdin is opened on container start, is empty until the first client
     attaches to stdin, and then remains open and accepts data until the client
     disconnects, at which time stdin is closed and remains closed until the
     container is restarted. If this flag is false, a container processes that
     reads from stdin will never receive an EOF. Default is false
   terminationMessagePath       <string>
     Optional: Path at which the file to which the container's termination
     message will be written is mounted into the container's filesystem. Message
     written is intended to be brief final status, such as an assertion failure
     message. Will be truncated by the node if greater than 4096 bytes. The
     total message length across all containers will be limited to 12kb.
     Defaults to /dev/termination-log. Cannot be updated.
   terminationMessagePolicy     <string>
     Indicate how the termination message should be populated. File will use the
     contents of terminationMessagePath to populate the container status message
     on both success and failure. FallbackToLogsOnError will use the last chunk
     of container log output if the termination message file is empty and the
     container exited with an error. The log output is limited to 2048 bytes or
     80 lines, whichever is smaller. Defaults to File. Cannot be updated.
   tty  <boolean>
     Whether this container should allocate a TTY for itself, also requires
     'stdin' to be true. Default is false.
   volumeDevices        <[]Object>
     volumeDevices is the list of block devices to be used by the container.
     This is a beta feature.
   volumeMounts <[]Object>
     Pod volumes to mount into the container's filesystem. Cannot be updated.
   workingDir   <string>
     Container's working directory. If not specified, the container runtime's
     default will be used, which might be configured in the container image.
     Cannot be updated.

可以看到对前面的yaml中的image、name、ports等做了详细解释。读者可以试试

kubectl explain pods.spec.dnsPolicy

等命令的帮助。

更多k8s相关内容,请看文章:k8s学习-思维导图与学习笔记

参考

k8s-理解k8s对资源象

k8s-标签和筛选器

k8s-注解

k8s-标签、注解和污点

github-api约定

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