文档说明
本文面向容器初学者，作者先简单的 用MySQL官方镜像搭建一个可运行的单实例数据库，而后考虑生产或现实需求，一步一步完善并揉合K8S多个技术，从而构建一个复杂且可供生产用的MySQL单实例库。
简单部署
如下所示，我们仅需设置root用户密码（环境变量MYSQL_ROOT_PASSWORD）， 便可轻松的使用MySQL官方镜像构建一个MySQL数据库。
# kubectl create -f - <<EOF
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
labels:
app: mysql
name: mysql
spec:
replicas: 1
selector:
matchLabels:
app: mysql
template:
metadata:
labels:
app: mysql
spec:
containers:
- image: mysql
name: mysql
imagePullPolicy: IfNotPresent
env:
- name: MYSQL_ROOT_PASSWORD
value: Changeme
EOF 注意：若你的K8S集群是minishift、openshift、origin，因其为安全考虑，不允许容器以root用户运行，而官方MySQL镜像却需root权限，故为使其能顺利运行，我们需将anyuid scc赋予default serviceaccount：
# oc adm policy add-scc-to-user anyuid -z default 创建一Service以便集群内外均可访问数据库，其中集群外需通过nodePort设置的30006端口访问。
# kubectl create -f - <<EOF
apiVersion: v1
kind: Service
metadata:
labels:
app: mysql
name: mysql
spec:
type: NodePort
ports:
- port: 3306
nodePort: 30006
protocol: TCP
targetPort: 3306
selector:
app: mysql
EOF 接着，访问数据库并验证其运行正常：
# kubectl get pod # 当前Pod名称
NAME READY STATUS RESTARTS AGE
mysql-5b5668c448-t44ml 1/1 Running 0 3h
# 通过本机访问 # kubectl exec -it mysql-5b5668c448-t44ml -- mysql -uroot -pChangeme
mysql> select 1;
+---+
| 1 |
+---+
| 1 |
+---+
# 集群内部通过mysql service访问： # kubectl exec -it mysql-5b5668c448-t44ml -- mysql -uroot -pChangeme -hmysql
mysql> select now();
+---------------------+
| now() |
+---------------------+
| 2018-05-21 07:19:14 |
+---------------------+
# 集群外部，可通过任何一个K8S节点访问数据库： # mysql -uroot -pChangeme -horigin-lb-01 -P30006
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+扩展部署
持久化存储
若要确保MySQL重启后数据仍然存在，我们需为其配置可持久化存储，作者的实验环境配置了GlusterFS分布式存储，其支持K8S动态提供特性，故可执行如下命令创建PVC：
# kubectl create -f - <<EOF
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
name: mysql
spec:
accessModes:
- ReadOnlyMany
resources:
requests:
storage: 1Gi
storageClassName: glusterfs-raid0
EOF 而后，调整Deploy并挂载卷：
spec: containers: - image: mysql ... volumeMounts: - name: mysql-data mountPath: /var/lib/mysql volumes: - name: mysql-data persistentVolumeClaim: claimName: mysql自定义配置文件
通过创建cm并挂载到容器中，我们可自定义MySQL配置文件。如下所示，名为mysql-config的cm包含一个custom.cnf文件：
apiVersion: v1 metadata: name: mysql-config data: custom.cnf: | [mysqld] default_storage_engine=innodb skip_external_locking lower_case_table_names=1 skip_host_cache skip_name_resolve kind: ConfigMap 将cm挂载到容器内：
spec: ... containers: - image: mysql ... volumeMounts: - name: mysql-config mountPath: /etc/mysql/conf.d/ ... volumes: - name: mysql-config configMap: name: mysql-config ...加密铭感数据
用户密码等铭感数据以Secret加密保存，而后被Deployment通过volume挂载或环境变量引用。如本例，我们创建root、app 、test用户，将3个用户的密码加密保存：
# echo -n Changeme | base64
Q2hhbmdlbWU=
# kubectl create -f - <<EOF
apiVersion: v1
kind: Secret
metadata:
name: mysql-user-pwd
data:
mysql-root-pwd: Q2hhbmdlbWU=
mysql-app-user-pwd: Q2hhbmdlbWU=
mysql-test-user-pwd: Q2hhbmdlbWU=
EOF Secret创建完成后，我们将用户明文密码从Deployment去除，采用环境变量方式引用Secret数据，参见如下Yaml修改，做了3个调整：
- 镜像初始化时自动创建MYSQL_DATABASE环境变量1设置的数据库；
- 镜像初始化时将MYSQL_DATABASE数据库赋予MYSQL_USER用户；
- root用户及MYSQL_USER用户，其密码均通过secretKeyRef从secret获取；
spec: ... containers: - image: mysql name: mysql imagePullPolicy: IfNotPresent env: - name: MYSQL_ROOT_PASSWORD valueFrom: secretKeyRef: name: mysql-user-pwd key: mysql-root-pwd - name: MYSQL_PASSWORD valueFrom: secretKeyRef: name: mysql-user-pwd key: mysql-app-user-pwd - name: MYSQL_USER value: app - name: MYSQL_DATABASE value: appdb容器健康检查
K8S镜像控制器可通过livenessProbe判断容器是否异常，进而决定是否重建容器；而Service服务可通过readinessProbe判断容器服务是否正常，从而确保服务可用性。
本例，作者配置的livenessProbe与readinessProbe是一样的，即连续3次查询数据库失败，则定义为异常。对livenessProbe与readinessProbe详细用法，不在本文的讨论范围内，可参考K8S官方文档：
spec: containers: - image: mysql ... livenessProbe: exec: command: - /bin/sh - "-c" - MYSQL_PWD="${MYSQL_ROOT_PASSWORD}" - mysql -h 127.0.0.1 -u root -e "SELECT 1" initialDelaySeconds: 30 timeoutSeconds: 5 successThreshold: 1 failureThreshold: 3 readinessProbe: exec: command: - /bin/sh - "-c" - MYSQL_PWD="${MYSQL_ROOT_PASSWORD}" - mysql -h 127.0.0.1 -u root -e "SELECT 1" initialDelaySeconds: 10 timeoutSeconds: 1 successThreshold: 1 failureThreshold: 3 ...容器初始化
假设，我们有这样的需求：“初始部署MySQL时，其已包应用所需的数据库、用户、权限、表结构与数据”。研究MySQL官方镜像的Dockerfile可知，数据库初始化时将自动执行目录/docker-entrypoint-initdb.d内的.sh、.sql、.sql.gz文件，鉴于此，我们可有如下两种方法：
- 基于官方镜像重新编写Dockerfile，将脚本copy到新镜像/docker-entrypoint-initdb.d目录，因需编译新镜像，故此方法不灵活；
- 初始化容器（initContainers）在常规容器（containers）前运行，故在初始化容器中可将脚本拷贝到共享目录，而后MySQL镜像挂载此目录到/docker-entrypoint-initdb.d，此方法灵活。
本例，作者采用初始化容器方案，功能如下：
- 初始化与常规容器共享名为mysql-initdb的emptyDir，均被挂载到/docker-entrypoint-initdb.d目录；
- 初始化容器将.sql文件置于共享的/docker-entrypoint-initdb.d目录，其含初始化testdb与appdb数据库；
- 为了避免MySQL数据库目录内的lost+found目录被误认为是数据库，初始化容器中将其删除；
spec: initContainers: - name: mysql-init image: busybox imagePullPolicy: IfNotPresent env: - name: MYSQL_TEST_USER_PASSWORD valueFrom: secretKeyRef: name: mysql-user-pwd key: mysql-test-user-pwd command: - sh - "-c" - | set -ex rm -fr /var/lib/mysql/lost+found cat > /docker-entrypoint-initdb.d/mysql-testdb-init.sql <<EOF create database testdb default character set utf8; grant all on testdb.* to 'test'@'%' identified by '$MYSQL_TEST_USER_PASSWORD'; flush privileges; EOF cat > /docker-entrypoint-initdb.d/mysql-appdb-init.sql <<EOF create table app(id int); insert into app values(1); commit; EOF volumeMounts: - name: mysql-data mountPath: /var/lib/mysql - name: mysql-initdb mountPath: /docker-entrypoint-initdb.d containers: - image: mysql volumeMounts: - name: mysql-initdb mountPath: /docker-entrypoint-initdb.d ... volumes: - name: mysql-data persistentVolumeClaim: claimName: mysql - name: mysql-initdb emptyDir: {} ...完整Deployment
通过如上多步调整，MySQL数据库的Deplyment如下所示：
apiVersion: extensions/v1beta1 kind: Deployment metadata: labels: app: mysql name: mysql spec: replicas: 1 selector: matchLabels: app: mysql template: metadata: labels: app: mysql spec: initContainers: - name: mysql-init image: busybox imagePullPolicy: IfNotPresent env: - name: MYSQL_TEST_USER_PASSWORD valueFrom: secretKeyRef: name: mysql-user-pwd key: mysql-test-user-pwd command: - sh - "-c" - | set -ex rm -fr /var/lib/mysql/lost+found cat > /docker-entrypoint-initdb.d/mysql-testdb-init.sql <<EOF create database testdb default character set utf8; grant all on testdb.* to 'test'@'%' identified by '$MYSQL_TEST_USER_PASSWORD'; flush privileges; EOF cat > /docker-entrypoint-initdb.d/mysql-appdb-init.sql <<EOF create table app(id int); insert into app values(1); commit; EOF volumeMounts: - name: mysql-data mountPath: /var/lib/mysql - name: mysql-initdb mountPath: /docker-entrypoint-initdb.d containers: - image: mysql name: mysql imagePullPolicy: IfNotPresent env: - name: MYSQL_ROOT_PASSWORD valueFrom: secretKeyRef: name: mysql-user-pwd key: mysql-root-pwd - name: MYSQL_PASSWORD valueFrom: secretKeyRef: name: mysql-user-pwd key: mysql-app-user-pwd - name: MYSQL_USER value: app - name: MYSQL_DATABASE value: appdb volumeMounts: - name: mysql-data mountPath: /var/lib/mysql - name: mysql-initdb mountPath: /docker-entrypoint-initdb.d - name: mysql-config mountPath: /etc/mysql/conf.d/ ports: - name: mysql containerPort: 3306 command: - /bin/sh - "-c" - MYSQL_PWD="${MYSQL_ROOT_PASSWORD}" - mysql -h 127.0.0.1 -u root -e "SELECT 1" initialDelaySeconds: 30 timeoutSeconds: 5 successThreshold: 1 failureThreshold: 3 readinessProbe: exec: command: - /bin/sh - "-c" - MYSQL_PWD="${MYSQL_ROOT_PASSWORD}" - mysql -h 127.0.0.1 -u root -e "SELECT 1" initialDelaySeconds: 10 timeoutSeconds: 1 successThreshold: 1 failureThreshold: 3 volumes: - name: mysql-data persistentVolumeClaim: claimName: mysql - name: mysql-initdb emptyDir: {} - name: mysql-config configMap: name: mysql-config创建此Deployment后，我们有如下组件：
# kubectl get all,pvc,cm,secret # MySQL Deployment：
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
deploy/mysql 1 1 1 1 1m
# RS被Deployment调用，其是自动生成的
NAME DESIRED CURRENT READY AGE
rs/mysql-998977cdd 1 1 1 1m
# Pod：
NAME READY STATUS RESTARTS AGE
po/mysql-998977cdd-v2ks2 1/1 Running 1 1m
# Service：
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
svc/mysql NodePort 172.30.3.200 <none> 3306:30006/TCP 8h
# Pvc：
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
pvc/mysql Bound pvc-fe.. 1Gi ROX glusterfs-raid0 2m
# Configmap：
NAME DATA AGE
cm/mysql-config 1 6h
# Secret：
NAME TYPE DATA AGE
secrets/mysql-user-pwd Opaque 3 1h定期自动备份
考虑到数据安全性，我们定期备份数据库，在K8S集群中，我们可配置CronJob实现自动备份作业。首先，创建一个持久化存储供备份用：
# kubectl create -f - <<EOF
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
name: mysql-backup
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 2Gi
storageClassName: glusterfs-raid0
EOF 继而，配置实际的自动化作业任务，如下所示，每天凌晨0点将使用mysqldump备份appdb数据库。
# kubectl create -f - <<EOF
apiVersion: batch/v1beta1
kind: CronJob
metadata:
name: mysql-backup
spec:
schedule: "0 0 * * *"
jobTemplate:
spec:
template:
spec:
containers:
- name: mysql-backup
imagePullPolicy: IfNotPresent
image: mysql
env:
- name: MYSQL_BACKUP_USER
value: root
- name: MYSQL_BACKUP_USER_PASSWORD
valueFrom:
secretKeyRef:
name: mysql-user-pwd
key: mysql-root-pwd
- name: MYSQL_HOST
value: mysql
command:
- /bin/sh
- -c
- |
set -ex
mysqldump --host=$MYSQL_HOST --user=$MYSQL_BACKUP_USER \
--password=$MYSQL_BACKUP_USER_PASSWORD \
--routines --databases appdb --single-transaction \
> /mysql-backup/mysql-`date +"%Y%m%d"`.sql
volumeMounts:
- name: mysql-backup
mountPath: /mysql-backup
restartPolicy: OnFailure
volumes:
- name: mysql-backup
persistentVolumeClaim:
claimName: mysql-backup
EOF结束语
本文揉合K8S多项技术，构建了一个复杂且可做生产使用的范例，当然，此库是单实例数据库，倘若需构建数据库高可用方案，需部署如MySQL HA、PXC集群，其中自动作业备份范例仅使用mysqldump备份，在生产环境不是很实用，我们需要考虑使用xtrabackup备份以及mysqlbinlog备份日志。
本文转自SegmentFault-在K8S集群中一步步构建一个复杂的MySQL数据库
