Stateful Set是Kubernetes 1.9版本新引入的一個概念，用于管理有狀態的應用。

Kubernetes官方文檔：

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由以下幾個部分組成：

1. 用于定義網絡標志（DNS domain）的Headless Service

2. 用于創建PersistentVolumes的volumeClaimTemplates

3. 定義具體應用的StatefulSet

下面我給出了一個實際應用中的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

使用kubectl get statefulset查看生成的statefulset:

生成的headless service：

生成的pod：

當我把statefulset yaml文件里的replicas從1改成3之后，果然觀察到有兩個新的pod正在啟動，并且名稱滿足命名規范-X。

使用kubectl describe查看創建的statefulset明細：

statefulSet自動創建的persistentVolumeClaim：

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

使用下面的命令登錄到statefulset提供的postgreSQL服務器上：

1. kubectl run tester -it --rm --image=postgres:9.6 --env=“PGCONNECT_TIMEOUT=5” --command – bash

看到root$之后，說明我們已經連接上pod了。

使用如下命令行連接postgreSQL服務器：

psql -h ads-db-statefulset-0.ads-db-service -p 5432 -U adsuser -W ads

當然如果不用命令行，也可以使用pgadmin，以圖形化界面連接statefulSet里的postgreSQL服務器：

sudo apt install pgadmin3

進行端口轉發，這樣我們可以使用localhost：5432進行連接：

kubectl port-forward ads-db-statefulset-0 5432:5432

也能成功連接：

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總結

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