运行一个有状态应用 MySQL
通过创建StatefulSet实现 MySQL 运行一主多从，使用异步复制。
MySQL 使用不安全的默认配置，仅关心 Kubernetes 运行有状态服务的一般场景。
目标
- 使用
StatefulSet部署多副本的 MySQL - 测试客户端连接
- 修改副本数量
开始之前
- 需要有一个 Kubernetes 集群
- 需要有一个动态
PersistentVolume配置器，提供持久化存储以满足PersistentVolumeClaim。如果没有则需要手工创建PersistentVolume。
部署MySQL
这个用例中包括一个 ConfigMap，两个 Service，一个 StatefulSet。
ConfigMap
apiVersion: v1
kind: ConfigMap
metadata:
name: mysql
labels:
app: mysql
data:
master.cnf: |
# Apply this config only on the master.
[mysqld]
log-bin
slave.cnf: |
# Apply this config only on slaves.
[mysqld]
super-read-only
将上述的文件保存为 mysql-configmap.yaml，并通过以下命令应用：
kubectl apply -f mysql-configmap.yaml
这个 ConfigMap 提供了 my.cnf，允许独立控制 Master 和 Slave 的配置。这个配置中 Master 复制日志给 Slave，而 Slave 拒绝除了复制之外的任何写入。
ConfigMap 并不对不同的 Pod 做不同的配置，每个 Pod 根据 StatefulSet 控制器提供的信息决定在初始化时查看哪个部分。
Service
# Headless service for stable DNS entries of StatefulSet members.
apiVersion: v1
kind: Service
metadata:
name: mysql
labels:
app: mysql
spec:
ports:
- name: mysql
port: 3306
clusterIP: None
selector:
app: mysql
---
# Client service for connecting to any MySQL instance for reads.
# For writes, you must instead connect to the master: mysql-0.mysql.
apiVersion: v1
kind: Service
metadata:
name: mysql-read
labels:
app: mysql
spec:
ports:
- name: mysql
port: 3306
selector:
app: mysql
将上述的文件保存为 mysql-services.yaml，并通过以下命令应用：
kubectl apply -f mysql-services.yaml
Headless Service 为 StatefulSet 创建的 Pod 提供了 DNS 解析。同一个集群，同一个命名空间下的 Pod 可以通过 <pod-name>.mysql 来访问 mysql 服务下的 Pod。
mysql-read 是一个普通服务，它有自己的 Cluster IP，可以给所有状态为 Ready 的 Pod 分配连接，包括 Master 和所有 Slave。
只有读才能使用 mysql-read。因为只有一个 Master 所以客户端需要通过 Headless Service 直接连接 Master Pod。
StatefulSet
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: mysql
spec:
selector:
matchLabels:
app: mysql
serviceName: mysql
replicas: 3
template:
metadata:
labels:
app: mysql
spec:
initContainers:
- name: init-mysql
image: mysql:5.7
command:
- bash
- "-c"
- |
set -ex
# Generate mysql server-id from pod ordinal index.
[[ `hostname` =~ -([0-9]+)$ ]] || exit 1
ordinal=${BASH_REMATCH[1]}
echo [mysqld] > /mnt/conf.d/server-id.cnf
# Add an offset to avoid reserved server-id=0 value.
echo server-id=$((100 + $ordinal)) >> /mnt/conf.d/server-id.cnf
# Copy appropriate conf.d files from config-map to emptyDir.
if [[ $ordinal -eq 0 ]]; then
cp /mnt/config-map/master.cnf /mnt/conf.d/
else
cp /mnt/config-map/slave.cnf /mnt/conf.d/
fi
volumeMounts:
- name: conf
mountPath: /mnt/conf.d
- name: config-map
mountPath: /mnt/config-map
- name: clone-mysql
image: gcr.io/google-samples/xtrabackup:1.0
command:
- bash
- "-c"
- |
set -ex
# Skip the clone if data already exists.
[[ -d /var/lib/mysql/mysql ]] && exit 0
# Skip the clone on master (ordinal index 0).
[[ `hostname` =~ -([0-9]+)$ ]] || exit 1
ordinal=${BASH_REMATCH[1]}
[[ $ordinal -eq 0 ]] && exit 0
# Clone data from previous peer.
ncat --recv-only mysql-$(($ordinal-1)).mysql 3307 | xbstream -x -C /var/lib/mysql
# Prepare the backup.
xtrabackup --prepare --target-dir=/var/lib/mysql
volumeMounts:
- name: data
mountPath: /var/lib/mysql
subPath: mysql
- name: conf
mountPath: /etc/mysql/conf.d
containers:
- name: mysql
image: mysql:5.7
env:
- name: MYSQL_ALLOW_EMPTY_PASSWORD
value: "1"
ports:
- name: mysql
containerPort: 3306
volumeMounts:
- name: data
mountPath: /var/lib/mysql
subPath: mysql
- name: conf
mountPath: /etc/mysql/conf.d
resources:
requests:
cpu: 500m
memory: 1Gi
livenessProbe:
exec:
command: ["mysqladmin", "ping"]
initialDelaySeconds: 30
periodSeconds: 10
timeoutSeconds: 5
readinessProbe:
exec:
# Check we can execute queries over TCP (skip-networking is off).
command: ["mysql", "-h", "127.0.0.1", "-e", "SELECT 1"]
initialDelaySeconds: 5
periodSeconds: 2
timeoutSeconds: 1
- name: xtrabackup
image: gcr.io/google-samples/xtrabackup:1.0
ports:
- name: xtrabackup
containerPort: 3307
command:
- bash
- "-c"
- |
set -ex
cd /var/lib/mysql
# Determine binlog position of cloned data, if any.
if [[ -f xtrabackup_slave_info ]]; then
# XtraBackup already generated a partial "CHANGE MASTER TO" query
# because we're cloning from an existing slave.
mv xtrabackup_slave_info change_master_to.sql.in
# Ignore xtrabackup_binlog_info in this case (it's useless).
rm -f xtrabackup_binlog_info
elif [[ -f xtrabackup_binlog_info ]]; then
# We're cloning directly from master. Parse binlog position.
[[ `cat xtrabackup_binlog_info` =~ ^(.*?)[[:space:]]+(.*?)$ ]] || exit 1
rm xtrabackup_binlog_info
echo "CHANGE MASTER TO MASTER_LOG_FILE='${BASH_REMATCH[1]}',\
MASTER_LOG_POS=${BASH_REMATCH[2]}" > change_master_to.sql.in
fi
# Check if we need to complete a clone by starting replication.
if [[ -f change_master_to.sql.in ]]; then
echo "Waiting for mysqld to be ready (accepting connections)"
until mysql -h 127.0.0.1 -e "SELECT 1"; do sleep 1; done
echo "Initializing replication from clone position"
# In case of container restart, attempt this at-most-once.
mv change_master_to.sql.in change_master_to.sql.orig
mysql -h 127.0.0.1 <<EOF
$(<change_master_to.sql.orig),
MASTER_HOST='mysql-0.mysql',
MASTER_USER='root',
MASTER_PASSWORD='',
MASTER_CONNECT_RETRY=10;
START SLAVE;
EOF
fi
# Start a server to send backups when requested by peers.
exec ncat --listen --keep-open --send-only --max-conns=1 3307 -c \
"xtrabackup --backup --slave-info --stream=xbstream --host=127.0.0.1 --user=root"
volumeMounts:
- name: data
mountPath: /var/lib/mysql
subPath: mysql
- name: conf
mountPath: /etc/mysql/conf.d
resources:
requests:
cpu: 100m
memory: 100Mi
volumes:
- name: conf
emptyDir: {}
- name: config-map
configMap:
name: mysql
volumeClaimTemplates:
- metadata:
name: data
spec:
accessModes: ["ReadWriteOnce"]
resources:
requests:
storage: 10Gi
将上述的文件保存为 mysql-statefulset.yaml，并通过以下命令应用：
kubectl apply -f mysql-statefulset.yaml
通过以下命令观察启动顺序：
kubectl get pods -w -l app=mysql
经过一段时间后 3 个 Pod 应该处于 Running 状态：
NAME READY STATUS RESTARTS AGE
mysql-0 2/2 Running 0 2m
mysql-1 2/2 Running 0 1m
mysql-2 2/2 Running 0 1m
如果没有看到任何进程，确保启用了动态 PersistentVolume 配置器。
如果没有动态 PersistentVolume 配置器，则需要手动创建 PersistentVolume
PersistentVolume (optional)
---
kind: PersistentVolume
apiVersion: v1
metadata:
name: mysql-pv-0
lables:
type: local
spec:
capacity:
storage: 10Gi
accessModes:
- ReadWriteOnce
hostPath:
path: "/mnt/mysql/0"
根据副本数可能需要创建多个 PersistenVolume。
将上述的文件保存为 mysql-pv.yaml，并通过以下命令应用：
kubectl apply -f mysql-pv.yaml
Capacity
定义了 PV 的容量
AccessModes
- ReadWriteOnece - 只能以读写模式挂载给一个节点
- ReadOnlyMany - 以只读模式挂载给许多节点
- ReadWriteMany - 以读写模式挂载给许多节点
了解有状态Pod初始化
StatefulSet 控制器顺序启动 Pod，当一个 Pod 为 Ready 状态后再启动下一个。
控制器给每个 Pod 分配一个固定的名称 <statefulset-name>-<ordinal-index>，例如 mysql-0，mysql-1
测试客户端连接
测试写入
kubectl run mysql-client --image=mysql:5.7 -i --rm --restart=Never --\
mysql -h mysql-0.mysql <<EOF
CREATE DATABASE test;
CREATE TABLE test.messages (message VARCHAR(250));
INSERT INTO test.messages VALUES ('hello');
EOF
使用 mysql-read 作为主机名测试读取
kubectl run mysql-client --image=mysql:5.7 -i -t --rm --restart=Never --\
mysql -h mysql-read -e "SELECT * FROM test.messages"
测试 mysql-read 分发连接给各个 Pod
kubectl run mysql-client-loop --image=mysql:5.7 -i -t --rm --restart=Never --\
bash -ic "while sleep 1; do mysql -h mysql-read -e 'SELECT @@server_id,NOW()'; done"
修改副本数量
修改副本数至 5：
kubectl scale statefulset mysql --replicas=5
或者修改 mysql-statefulset.yaml 后重新应用
10c10
< replicas: 3
---
> replicas: 5
kubectl applyt -f mysql-statefulset.yaml
清理
- 删除 StatefulSet，会同时删除由 StatefulSet 生成的 Pod
- 删除 Service
- 删除 PersistentVoluem，如果是手动创建的
- 删除 ConfigMap
kubectl delete StatefulSet mysql
kubectl detete Service mysql mysql-read
kubectl delete PersistentVolume mysql-pv-0
也可由配置文件删除
kubectl delete -f mysql-statefulset.yaml
kubectl delete -f mysql-services.yaml
kubectl delete -f mysql-pv.yaml
kubectl delete -f mysql-configmap.yaml