So recently I got involved with an ASP.NET project which was build over 10 years ago and over the years Developers and Change Requests came and went. And over the period the Application became quite cumbersome and quite hard to understand and manage, the Application became quite large in terms of functionality, codebase and data.
It was cumbersome and quite hard to understand for a new developer and manage for the Ops team. Lot of technical debts started accumulating because there was no real time spend on optimizing or refactoring the systems. The database was slow and deadlocks were becoming normal. It was hosted on huge on-premise hardware making it a heavy and costly solution.
The management realized this and decided it was a time for a refresh. The plan was made to look at utilizing the cloud technologies. And I joined the project as the software architect for the upgrade/migration.
In this article the focus is on Data and I am putting down my thoughts on what would be the right Cloud Data architecture for this organization.
Let's start with categorizing Data, Use case and the corresponding system.
Datastore can be categorized into two types of system.
And here is the Data Architecture diagram
This article is going to focus on item #3. The SQL Server Container. The others will be visited in future articles. So now we will walk-through on how to
Deploy SQL Server DB Instance into an AKS Cluster.
Databases are stateful. That means it needs storage that can be persisted. So we will first look at storage.
Applications hosted on Azure Kubernetes Service (AKS) may need to store and retrieve data.
The data storage requirements of many types:
Below we will address four concepts that provides storage to
applications in AKS
This is the storage and in Azure it comes in two forms.
For our SQL Server container we will creating an Azure Disk for the data storage requirements.
A persistent volume is a storage resource that is managed by the Kubernetes Master API that can exist beyond the lifetime of Pod. It can be statically created by Kubernetes cluster or dynamically provisioned. We will be looking at static provisioning.
apiVersion: v1 kind: PersistentVolume metadata: name: azure-disk-pv namespace: db spec: capacity: storage: 80Gi storageClassName: "" volumeMode: Filesystem accessModes: - ReadWriteOnce azureDisk: kind: Managed diskName: Kube_static_disk diskURI: /subscriptions/15cxx96af-xxxxx-xxx-a760-1f58cxxxxxfe/resourceGroups/MC_maltax_southeastasia/providers/Microsoft.Compute/disks/Kube_static_disk
Storage Classes (SC)
A storage class defines the tier (Premium/Standard), Access Modes. Reclaim policy.
Persistent Volume Claim (PVC)
When an application requires some persistent storage from AKS it has an issue a claim or Persistent Volume Claim. This has to define the
Storage Class, Access Mode and Size.
If the annotation like below is set in the PVC; then Kubernetes will try to dynamically create the resource. Assuming a matching storageclass called my-storage-class is found.
But in our case, we are going for Static provisioning. We already created an Azure Disk earlier 80GB size. We also created the Persistent Volume (PV).
Now let’s create a Persistent Volume Claim (PVC).
apiVersion: v1 kind: PersistentVolumeClaim metadata: name: mssql-data-pvc namespace: db spec: storageClassName: "" accessModes: - ReadWriteOnce resources: requests: storage: 80Gi
As you can we don't have the annotation for Dynamic provisioning. Instead Kubernetes will map this PVC with earlier created PV.
The above screenshot confirms the PVC is mapped to PV. Or the claim is mapped to real storage(disk).
Now we got storage sorted. Let's deploy the SQL Server Container onto Kubernetes. Below is the file that has the Kubernetes SQL Server Deployment and Service details. Check the section under Volumes.
apiVersion: apps/v1beta1 kind: Deployment metadata: name: mssql-deployment namespace: db spec: replicas: 1 template: metadata: labels: app: mssql spec: terminationGracePeriodSeconds: 10 containers: - name: mssql image: mcr.microsoft.com/mssql/server:2017-latest ports: - containerPort: 1433 env: - name: MSSQL_PID value: "Developer" - name: ACCEPT_EULA value: "Y" - name: SA_PASSWORD valueFrom: secretKeyRef: name: mssql key: SA_PASSWORD volumeMounts: - name: mssqldb mountPath: /var/opt/mssql volumes: - name: mssqldb persistentVolumeClaim: claimName: mssql-data-pvc --- apiVersion: v1 kind: Service metadata: name: mssql-deployment namespace: db spec: selector: app: mssql ports: - protocol: TCP port: 1433 targetPort: 1433 type: LoadBalancer
We will deploy this. See below screenshot.
We can see after around 40 seconds the SQL Server Instance is up and running. We are able to connect using sqlcmd command.
We can also see that the pod is running on the VM and below screenshot shows that the VM has mounted the storage disk that we provisioned earlier.
Now SQL Server is set up and running; let's look at some key parameters.
In AKS a feature called Azure Accelerated Networking is turned by default. Since the Applications and our SQL Server Container Instance are deployed in the same AKS instance we are automatically able to gain this benefits of this feature.
Another way to gain performance is to use Ultra SSD which scale
performance up to 160,000* IOPS and 2 GB/s per disk with zero downtime.
Kubernetes regularly check whether the SQL Server Containers Instance are running healthy. If for some reason the instance crashes or stop being responsive.
Kubernetes restarts it. When I tried to delete a Sql Server Pod; Kubernetes instantly detected and spun a new Pod within 4 seconds. See below screenshot.
Our storage for the container is Azure Disks which provides an SLA of 99.999% and had no outage till now. But still we should be prepared for a Disaster. One of the options we have to take regular incremental snapshots of Azure Disks. If a disaster strikes, we can restore the most snapshot back to a Disk.
This Disk can be then mounted onto a new SQL Server Instance. But since we have the data (maybe old by a few mins or hours based on our Recovery Point Objective (RPO) of Disaster Recovery strategy).
Another way to get back up and running when a disaster strikes is to use SqlPackage command. We can regular backups (automated). Disaster strikes we can spin up a new SQL Server Instance and Azure Disk Storage. Then we will restore the bacpac file back on to the Azure Disk for use by SQL Server.
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