Kubernetes stateful set講解以及一個基於postgreSQL的具體例子

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

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由如下幾個部分組成：

1. 用於定義網絡標誌（DNS domain）的Headless Service

2. 用於建立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/v1

kind: StatefulSet

metadata:

name: ads-db-statefulset

labels:

component: ads

module: db

spec:

serviceName: ads-db-service

replicas: 1

selector:

matchLabels:

component: ads

module: db

template:

metadata:

labels:

component: ads

module: db

spec:

volumes:

- name: init

secret:

secretName: ads-db-secret

items:

- key: initdb.sql

path: initdb.sql

containers:

- name: ads-db-pod

image: postgres:9.6

ports:

- containerPort: 5432

name: ads-db-port

volumeMounts:

- name: ads-db-volume

mountPath: /var/lib/postgresql/data/

- name: init

mountPath: /docker-entrypoint-initdb.d/

env:

- name: PGDATA

valueFrom:

configMapKeyRef:

name: ads-db-configmap

key: pgdata_value

- name: POSTGRES_PASSWORD

valueFrom:

secretKeyRef:

name: ads-db-secret

key: postgres_password_value

volumeClaimTemplates:

- metadata:

name: ads-db-volume

labels:

component: ads

module: db

spec:

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文件裏的replicas從1改爲3以後，果真觀察到有兩個新的pod正在啓動，而且名稱知足命名規範<stateful set name >-X。

使用kubectl describe查看建立的statefulset明細：

statefulSet自動建立的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

使用下面的命令登陸到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$以後，說明咱們已經鏈接上pod了。

使用以下命令行鏈接postgreSQL服務器：

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

固然若是不用命令行，也能夠使用pgadmin，以圖形化界面鏈接statefulSet裏的postgreSQL服務器：

sudo apt install pgadmin3

進行端口轉發，這樣咱們能夠使用localhost：5432進行鏈接：

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

也能成功鏈接：

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