I am trying to have a scalable mysql DB whith persistent memory. I thought it was something common, but it seems like online no one really explains it. I am using minikube for my single node cluster. I started off from the kubernetes guide on how to run replicated stateful applications but it does not really get into the persistent volume creation. I have created the configmap like the one in the guide:
apiVersion: v1
kind: ConfigMap
metadata:
name: mysql
labels:
app: mysql
data:
primary.cnf: |
# Apply this config only on the primary.
[mysqld]
log-bin
replica.cnf: |
# Apply this config only on replicas.
[mysqld]
super-read-only
And the two serivces:
# 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 primary: mysql-0.mysql.
apiVersion: v1
kind: Service
metadata:
name: mysql-read
labels:
app: mysql
spec:
ports:
- name: mysql
port: 3306
selector:
app: mysql
I needed to initialize the schema of my database, so I made this configmap to pass inside the statefulset:
apiVersion: v1
kind: ConfigMap
metadata:
name: mysql-initdb-config
data:
initdb.sql: |
CREATE DATABASE football;
CREATE TABLE `squadra` (
`name` varchar(15) PRIMARY KEY NOT NULL
);
USE football;
...
I created a storageclass and a persistent volume, thanks to this answer.
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: local-storage
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer
---
apiVersion: v1
kind: PersistentVolume
metadata:
name: pv-volume
spec:
storageClassName: local-storage
accessModes:
- ReadWriteOnce
capacity:
storage: 5Gi
hostPath:
path: /data/mysql_data/
And made a secret containing the password to the root user of my db:
apiVersion: v1
kind: Secret
metadata:
name: mysql-pass-root
type: kubernetes.io/basic-auth
stringData:
username: root
password: password
My statefulset I have was substantially taken from some answer on stackoverflow I am not finding anymore. It was basically a modification of the one on the kubernetes website. What I added is the database schema initialization, the volumeclaimtemplate and the password from the secret:
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: mysql
spec:
selector:
matchLabels:
app: mysql
serviceName: mysql
replicas: 2
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 [[ $ordinal -eq 0 ]]; then
cp /mnt/config-map/primary.cnf /mnt/conf.d/
else
cp /mnt/config-map/replica.cnf /mnt/conf.d/
fi
volumeMounts:
- name: conf
mountPath: /mnt/conf.d
- name: config-map
mountPath: /mnt/config-map
- name: clone-mysql
image: gcr.io/google-samples/xtrabackup:1.0
command:
- bash
- "-c"
- |
set -ex
# Skip the clone if data already exists.
[[ -d /var/lib/mysql/mysql ]] && exit 0
# Skip the clone on master (ordinal index 0).
[[ `hostname` =~ -([0-9]+)$ ]] || exit 1
ordinal=${BASH_REMATCH[1]}
[[ $ordinal -eq 0 ]] && exit 0
# Clone data from previous peer.
ncat --recv-only mysql-$(($ordinal-1)).mysql 3307 | xbstream -x -C /var/lib/mysql
# Prepare the backup.
xtrabackup --prepare --target-dir=/var/lib/mysql
volumeMounts:
- name: data
mountPath: /var/lib/mysql
subPath: mysql
- name: conf
mountPath: /etc/mysql/conf.d
containers:
- name: mysql
image: mysql:5.7
env:
- name: MYSQL_ROOT_PASSWORD
valueFrom:
secretKeyRef:
name: mysql-pass-root
key: password
- name: MYSQL_USER
value: server
- name: MYSQL_DATABASE
value: medlor
ports:
- name: mysql
containerPort: 3306
volumeMounts:
- name: data
mountPath: /var/lib/mysql
subPath: mysql
- name: conf
mountPath: /etc/mysql/conf.d
- name: mysql-initdb
mountPath: /docker-entrypoint-initdb.d
resources:
requests:
cpu: 500m
memory: 100Mi
livenessProbe:
exec:
command: ["mysqladmin", "-uroot", "-p$MYSQL_ROOT_PASSWORD", "ping"]
initialDelaySeconds: 30
periodSeconds: 10
timeoutSeconds: 5
readinessProbe:
exec:
# Check we can execute queries over TCP (skip-networking is off).
command:
- /bin/sh
- -ec
- >-
mysql -hlocalhost -uroot -p$MYSQL_ROOT_PASSWORD -e'SELECT 1'
initialDelaySeconds: 5
periodSeconds: 2
timeoutSeconds: 1
- name: xtrabackup
image: gcr.io/google-samples/xtrabackup:1.0
env:
- name: MYSQL_ROOT_PASSWORD
valueFrom:
secretKeyRef:
name: mysql-pass-root
key: password
ports:
- name: xtrabackup
containerPort: 3307
command:
- bash
- "-c"
- |
set -ex
cd /var/lib/mysql
# Determine binlog position of cloned data, if any.
if [[ -f xtrabackup_slave_info ]]; then
# XtraBackup already generated a partial "CHANGE MASTER TO" query
# because we're cloning from an existing slave.
mv xtrabackup_slave_info change_master_to.sql.in
# Ignore xtrabackup_binlog_info in this case (it's useless).
rm -f xtrabackup_binlog_info
elif [[ -f xtrabackup_binlog_info ]]; then
# We're cloning directly from master. Parse binlog position.
[[ `cat xtrabackup_binlog_info` =~ ^(.*?)[[:space:]]+(.*?)$ ]] || 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 localhost -uroot -p$MYSQL_ROOT_PASSWORD -e "SELECT 1"; do sleep 1; done
echo "Initializing replication from clone position"
# In case of container restart, attempt this at-most-once.
mv change_master_to.sql.in change_master_to.sql.orig
mysql -h localhost -uroot -p$MYSQL_ROOT_PASSWORD <<EOF
$(<change_master_to.sql.orig),
MASTER_HOST='mysql-0.mysql',
MASTER_USER='root',
MASTER_PASSWORD='$MYSQL_ROOT_PASSWORD',
MASTER_CONNECT_RETRY=10;
START SLAVE USER='root' PASSWORD='$MYSQL_ROOT_PASSWORD';
EOF
fi
# Start a server to send backups when requested by peers.
exec ncat --listen --keep-open --send-only --max-conns=1 3307 -c \
"xtrabackup --backup --slave-info --stream=xbstream --host=127.0.0.1 --user=root --password=$MYSQL_ROOT_PASSWORD"
volumeMounts:
- name: data
mountPath: /var/lib/mysql
subPath: mysql
- name: conf
mountPath: /etc/mysql/conf.d
resources:
requests:
cpu: 100m
memory: 500Mi
volumes:
- name: conf
emptyDir: {}
- name: config-map
configMap:
name: mysql
- name: mysql-initdb
configMap:
name: mysql-initdb-config
volumeClaimTemplates:
- metadata:
name: data
spec:
accessModes: [ "ReadWriteOnce" ]
storageClassName: "local-storage"
resources:
requests:
storage: 1Gi
When I start up minikube, I run the following commands:
docker exec minikube mkdir data/mysql_data ->in order to create the folder where mysql saves the data inside the minikube container
minikube mount local_path_to_a_folder:/data/mysql_data -> to keep the mysql data in my physical storage too.
kubectl apply -f pv-volume.yaml (the volume I showed before)
kubectl apply -f database\mysql\mysql-configmap.yaml (the configmap from the guide)
kubectl apply -f database\mysql\mysql-initdb-config.yaml (my configmap with the db schema)
kubectl apply -f database\mysql\mysql-secret.yaml (the secret containing the db password)
kubectl apply -f database\mysql\mysql-services.yaml (the two services)
Now, when I run all these commands my MySql pod fails, and this is what I can see from the dashboard:
Although in the persistent volumes section I can see my volume has been claimed:
I must have understood something wrong and there must be a logic error in all of this, but I can't figure out what it is. Any help would be extremely appreciated.
