Deploy a SQL Server container in Kubernetes with Azure Kubernetes Services (AKS)

• 09/01/2020
• 8 minutes to read
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Applies to: SQL Server (all supported versions) - Linux

Learn how to configure a SQL Server instance on Kubernetes in Azure Kubernetes Service (AKS), with persistent storage for high availability (HA). The solution provides resiliency. If the SQL Server instance fails, Kubernetes automatically re-creates it in a new pod. Kubernetes also provides resiliency against a node failure.

This tutorial demonstrates how to configure a highly available SQL Server instance in a container on AKS.

HA solution on Kubernetes running in Azure Kubernetes Service

Kubernetes 1.6 and later has support for storage classes, persistent volume claims, and the Azure disk volume type. You can create and manage your SQL Server instances natively in Kubernetes. The example in this article shows how to create a deployment to achieve a high availability configuration similar to a shared disk failover cluster instance. In this configuration, Kubernetes plays the role of the cluster orchestrator. When a SQL Server instance in a container fails, the orchestrator bootstraps another instance of the container that attaches to the same persistent storage.

In the preceding diagram, mssql-server is a container in a pod. Kubernetes orchestrates the resources in the cluster. A replica set ensures that the pod is automatically recovered after a node failure. Applications connect to the service. In this case, the service represents a load balancer that hosts an IP address that stays the same after failure of the mssql-server.

In the following diagram, the mssql-server container has failed. As the orchestrator, Kubernetes guarantees the correct count of healthy instances in the replica set, and starts a new container according to the configuration. The orchestrator starts a new pod on the same node, and mssql-server reconnects to the same persistent storage. The service connects to the re-created mssql-server.

In the following diagram, the node hosting the mssql-server container has failed. The orchestrator starts the new pod on a different node, and mssql-server reconnects to the same persistent storage. The service connects to the re-created mssql-server.

Prerequisites

• Kubernetes cluster

  • The tutorial requires a Kubernetes cluster. The steps use kubectl to manage the cluster.

  • See Deploy an Azure Kubernetes Service (AKS) cluster to create and connect to a single-node Kubernetes cluster in AKS with kubectl.

  Note

  To protect against node failure, a Kubernetes cluster requires more than one node.

• Azure CLI 2.0.23

  • The instructions in this tutorial have been validated against Azure CLI 2.0.23.

Create an SA password

Create an SA password in the Kubernetes cluster. Kubernetes can manage sensitive configuration information, like passwords as secrets.

The following command creates a password for the SA account:

kubectl create secret generic mssql --from-literal=SA_PASSWORD="MyC0m9l&xP@ssw0rd"

Replace MyC0m9l&xP@ssw0rd with a complex password.

To create a secret in Kubernetes named mssql that holds the value MyC0m9l&xP@ssw0rd for the SA_PASSWORD, run the command.

Create storage

Configure a persistent volume and persistent volume claim in the Kubernetes cluster. Complete the following steps:

1. Create a manifest to define the storage class and the persistent volume claim. The manifest specifies the storage provisioner, parameters, and reclaim policy. The Kubernetes cluster uses this manifest to create the persistent storage.

   The following yaml example defines a storage class and persistent volume claim. The storage class provisioner is azure-disk, because this Kubernetes cluster is in Azure. The storage account type is Standard_LRS. The persistent volume claim is named mssql-data. The persistent volume claim metadata includes an annotation connecting it back to the storage class.

   kind: StorageClass
   apiVersion: storage.k8s.io/v1
   metadata:
        name: azure-disk
   provisioner: kubernetes.io/azure-disk
   parameters:
     storageaccounttype: Standard_LRS
     kind: Managed
   ---
   kind: PersistentVolumeClaim
   apiVersion: v1
   metadata:
     name: mssql-data
     annotations:
       volume.beta.kubernetes.io/storage-class: azure-disk
   spec:
     accessModes:
     - ReadWriteOnce
     resources:
       requests:
         storage: 8Gi
   

   Save the file (for example, pvc.yaml).

2. Create the persistent volume claim in Kubernetes.

   kubectl apply -f <Path to pvc.yaml file>
   

   <Path to pvc.yaml file> is the location where you saved the file.

   The persistent volume is automatically created as an Azure storage account, and bound to the persistent volume claim.

   

3. Verify the persistent volume claim.

   kubectl describe pvc <PersistentVolumeClaim>
   

   <PersistentVolumeClaim> is the name of the persistent volume claim.

   In the preceding step, the persistent volume claim is named mssql-data. To see the metadata about the persistent volume claim, run the following command:

   kubectl describe pvc mssql-data
   

   The returned metadata includes a value called Volume. This value maps to the name of the blob.

   

   The value for volume matches part of the name of the blob in the following image from the Azure portal:

   

4. Verify the persistent volume.

   kubectl describe pv
   

   kubectl returns metadata about the persistent volume that was automatically created and bound to the persistent volume claim.

Create the deployment

In this example, the container hosting the SQL Server instance is described as a Kubernetes deployment object. The deployment creates a replica set. The replica set creates the pod.

In this step, create a manifest to describe the container based on the SQL Server mssql-server-linux Docker image. The manifest references the mssql-server persistent volume claim, and the mssql secret that you already applied to the Kubernetes cluster. The manifest also describes a service. This service is a load balancer. The load balancer guarantees that the IP address persists after SQL Server instance is recovered.

1. Create a manifest (a YAML file) to describe the deployment. The following example describes a deployment, including a container based on the SQL Server container image.

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: mssql-deployment
   spec:
     replicas: 1
     selector:
        matchLabels:
          app: mssql
     template:
       metadata:
         labels:
           app: mssql
       spec:
         terminationGracePeriodSeconds: 30
         hostname: mssqlinst
         securityContext:
           fsGroup: 10001
         containers:
         - name: mssql
           image: mcr.microsoft.com/mssql/server:2019-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
   ---
   apiVersion: v1
   kind: Service
   metadata:
     name: mssql-deployment
   spec:
     selector:
       app: mssql
     ports:
       - protocol: TCP
         port: 1433
         targetPort: 1433
     type: LoadBalancer
   

   Copy the preceding code into a new file, named sqldeployment.yaml. Update the following values:

   • MSSQL_PID value: "Developer": Sets the container to run SQL Server Developer edition. Developer edition is not licensed for production data. If the deployment is for production use, set the appropriate edition (Enterprise, Standard, or Express).

     Note

     For more information, see How to license SQL Server.

   • persistentVolumeClaim: This value requires an entry for claimName: that maps to the name used for the persistent volume claim. This tutorial uses mssql-data.

   • name: SA_PASSWORD: Configures the container image to set the SA password, as defined in this section.

     valueFrom:
       secretKeyRef:
         name: mssql
         key: SA_PASSWORD
     

   When Kubernetes deploys the container, it refers to the secret named mssql to get the value for the password.

   • securityContext : A securityContext defines privilege and access control settings for a Pod or Container, in this case it is specified at the pod level, so all containers ( in this case only one) adhere to that security context. In the security context we define the fsGroup with the value 10001 ( which is the GID for mssql group) means, all processes of the container are also part of the supplementary group ID 10001(mssql). The owner for volume /var/opt/mssql and any files created in that volume will be Group ID 10001(mssql group).

   Note

   By using the LoadBalancer service type, the SQL Server instance is accessible remotely (via the internet) at port 1433.

   Save the file (for example, sqldeployment.yaml).

2. Create the deployment.

   kubectl apply -f <Path to sqldeployment.yaml file>
   

   <Path to sqldeployment.yaml file> is the location where you saved the file.

   

   The deployment and service are created. The SQL Server instance is in a container, connected to persistent storage.

   To view the status of the pod, type kubectl get pod.

   

   In the preceding image, the pod has a status of Running. This status indicates that the container is ready. This may take several minutes.

   Note

   After the deployment is created, it can take a few minutes before the pod is visible. The delay is because the cluster pulls the mssql-server-linux image from the Docker hub. After the image is pulled the first time, subsequent deployments might be faster if the deployment is to a node that already has the image cached on it.

3. Verify the services are running. Run the following command:

   kubectl get services 
   

   This command returns services that are running, as well as the internal and external IP addresses for the services. Note the external IP address for the mssql-deployment service. Use this IP address to connect to SQL Server.

   

   For more information about the status of the objects in the Kubernetes cluster, run:

   az aks browse --resource-group <MyResourceGroup> --name <MyKubernetesClustername>
   

4. You can also verify the container is running as non-root by running the following command:

   kubectl.exe exec <name of SQL POD> -it -- /bin/bash 
   

   and then run 'whoami' you should see the username as mssql. Which is a non-root user.

   whoami
   

Connect to the SQL Server instance

If you configured the container as described, you can connect with an application from outside the Azure virtual network. Use the sa account and the external IP address for the service. Use the password that you configured as the Kubernetes secret.

You can use the following applications to connect to the SQL Server instance.

• SSMS

• SSDT

• sqlcmd

  To connect with sqlcmd, run the following command:

  sqlcmd -S <External IP Address> -U sa -P "MyC0m9l&xP@ssw0rd"
  

  Replace the following values:

  • <External IP Address> with the IP address for the mssql-deployment service
  • MyC0m9l&xP@ssw0rd with your password

Verify failure and recovery

To verify failure and recovery, you can delete the pod. Do the following steps:

1. List the pod running SQL Server.

   kubectl get pods
   

   Note the name of the pod running SQL Server.

2. Delete the pod.

   kubectl delete pod mssql-deployment-0
   

   mssql-deployment-0 is the value returned from the previous step for pod name.

Kubernetes automatically re-creates the pod to recover a SQL Server instance, and connect to the persistent storage. Use kubectl get pods to verify that a new pod is deployed. Use kubectl get services to verify that the IP address for the new container is the same.

Summary

In this tutorial, you learned how to deploy SQL Server containers to a Kubernetes cluster for high availability.

Next steps