Kubernetes|Kubernetes stateful set讲解以及一个基于postgreSQL的具体例子 Kubernetesstatefulset讲解以及一个

Stateful Set是Kubernetes 1.9版本新引入的一个概念，用于管理有状态的应用。
Kubernetes官方文档：
https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/
Manages the deployment and scaling of a set of Pods, and provides guarantees about the ordering and uniqueness of these Pods.
Like a Deployment, a StatefulSet manages Pods that are based on an identical container spec. Unlike a Deployment, a StatefulSet maintains a sticky identity for each of their Pods. These pods are created from the same spec, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling.
StatefulSet由以下几个部分组成：
【Kubernetes|Kubernetes stateful set讲解以及一个基于postgreSQL的具体例子】1. 用于定义网络标志（DNS domain）的Headless Service
2. 用于创建PersistentVolumes的volumeClaimTemplates
3. 定义具体应用的StatefulSet
下面我给出了一个实际应用中的StatefulSet的yaml文件：

---apiVersion: apps/v1kind: StatefulSetmetadata:name: ads-db-statefulsetlabels:component: adsmodule: dbspec:serviceName: ads-db-servicereplicas: 1selector:matchLabels:component: adsmodule: dbtemplate:metadata:labels:component: adsmodule: dbspec:volumes:- name: initsecret:secretName: ads-db-secretitems:- key: initdb.sqlpath: initdb.sqlcontainers:- name: ads-db-podimage: postgres:9.6ports:- containerPort: 5432name: ads-db-portvolumeMounts:- name: ads-db-volumemountPath: /var/lib/postgresql/data/- name: initmountPath: /docker-entrypoint-initdb.d/env:- name: PGDATAvalueFrom:configMapKeyRef:name: ads-db-configmapkey: pgdata_value- name: POSTGRES_PASSWORDvalueFrom:secretKeyRef:name: ads-db-secretkey: postgres_password_valuevolumeClaimTemplates:- metadata:name: ads-db-volumelabels:component: adsmodule: dbspec:accessModes: [ "ReadWriteOnce" ]resources:requests:storage: 1Gi

Kubernetes|Kubernetes stateful set讲解以及一个基于postgreSQL的具体例子

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使用kubectl get statefulset查看生成的statefulset:

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生成的headless service：

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生成的pod：

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当我把statefulset yaml文件里的replicas从1改成3之后，果然观察到有两个新的pod正在启动，并且名称满足命名规范-X。

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使用kubectl describe查看创建的statefulset明细：

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statefulSet自动创建的persistentVolumeClaim：

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The files belonging to this database system will be owned by user "postgres".
This user must also own the server process.
The database cluster will be initialized with locale "en_US.utf8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".
Data page checksums are disabled.
fixing permissions on existing directory /var/lib/postgresql/data/pgdata ... ok
creating subdirectories ... ok
selecting default max_connections ... 100
selecting default shared_buffers ... 128MB
selecting dynamic shared memory implementation ... posix
creating configuration files ... ok
running bootstrap script ... ok
performing post-bootstrap initialization ... ok
syncing data to disk ... ok
Success. You can now start the database server using:
pg_ctl -D /var/lib/postgresql/data/pgdata -l logfile start
使用下面的命令登录到statefulset提供的postgreSQL服务器上：
1. kubectl run tester -it --rm --image=postgres:9.6 --env="PGCONNECT_TIMEOUT=5" --command -- bash