在K8S集群中一步步构建一个复杂的MySQL数据库
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。
- 参见docker-entrypoint.sh。 ↩
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