Re: When access single storage from multiple pods of MySQL give error

[DigiPrima Technologies]

The issue you're encountering arises because MySQL is not designed to be accessed simultaneously by multiple instances sharing the same data files due to its use of file locks and the InnoDB storage engine's architecture. Running multiple MySQL pods with shared storage in this way will lead to file locking issues, as you've experienced.

To run a highly available MySQL setup in Kubernetes, you should consider other patterns or technologies that support high availability and data consistency without direct shared access to storage. Here are some alternative approaches:

### 1. **MySQL Cluster (NDB Cluster)**
MySQL Cluster provides a high availability and scalability solution for MySQL. It uses a shared-nothing architecture with data nodes storing the data and SQL nodes accessing it.

**Setup MySQL Cluster in Kubernetes:**
- Deploy data nodes, SQL nodes, and management nodes in separate pods.
- Use Kubernetes services for intra-cluster communication.

However, MySQL Cluster is complex to set up and may be overkill for many use cases.

### 2. **Galera Cluster**
Galera Cluster is a synchronous multi-master cluster for MySQL. It ensures that all nodes are consistent and can handle read and write operations.

**Setup Galera Cluster in Kubernetes:**
- Use StatefulSets to deploy Galera Cluster nodes.
- Ensure proper networking for replication.
- Use Persistent Volumes for data storage.

### 3. **Vitess**
Vitess is a database clustering system for horizontal scaling of MySQL through sharding. It’s designed to run on Kubernetes and handle large-scale deployments.

**Setup Vitess in Kubernetes:**
- Use the Vitess operator to manage clusters.
- Automate the deployment and management of shards and tablets.
- Handle failover and scaling seamlessly.

### 4. **Cloud-Managed MySQL Services**
Consider using a managed MySQL service such as Amazon RDS, Google Cloud SQL, or Azure Database for MySQL. These services provide high availability, automated backups, and scaling without the need for complex setups.

### Example of Galera Cluster in Kubernetes

Here’s a simplified example to set up a Galera Cluster using StatefulSets:

1. **Create Persistent Volumes and Claims:**

```yaml
apiVersion: v1
kind: PersistentVolume
metadata:
name: galera-pv-0
spec:
capacity:
storage: 1Gi
accessModes:
- ReadWriteOnce
hostPath:
path: "/mnt/data/galera-0"
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: galera-pvc-0
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
```

2. **Deploy Galera StatefulSet:**

```yaml
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: galera
spec:
selector:
matchLabels:
app: galera
serviceName: galera
replicas: 3
template:
metadata:
labels:
app: galera
spec:
containers:
- name: galera
image: codership/galera
ports:
- containerPort: 3306
- containerPort: 4444
- containerPort: 4567
- containerPort: 4568
volumeMounts:
- name: galera-storage
mountPath: /var/lib/mysql
env:
- name: MYSQL_ROOT_PASSWORD
value: pwd
volumeClaimTemplates:
- metadata:
name: galera-storage
spec:
accessModes: ["ReadWriteOnce"]
resources:
requests:
storage: 1Gi
```

3. **Create a Headless Service for StatefulSet:**

```yaml
apiVersion: v1
kind: Service
metadata:
name: galera
spec:
clusterIP: None
selector:
app: galera
ports:
- port: 3306
name: mysql
- port: 4444
name: sst
- port: 4567
name: replication
- port: 4568
name: ist
```

4. **Deploy the StatefulSet and Service:**

```sh
kubectl apply -f galera-pv.yaml
kubectl apply -f galera-pvc.yaml
kubectl apply -f galera-statefulset.yaml
kubectl apply -f galera-service.yaml
```

This setup will give you a Galera Cluster with three nodes, each with its own PersistentVolume, ensuring high availability and redundancy.