Deploying SQL Server Availability Groups in Kubernetes

In this blog post, we’re going to work on deploying a SQL Server Availability Group in a Kubernetes Cluster in on-premises virtual machines. I’m going to walk you through the process as it’s documented by Microsoft at this link here. This document is very good but only shows you how to do it in Azure, we’re going to do it in VMs. I’m going to follow Microsoft’s documentation as much as possible, deviating only when necessary for on-premises deployments. I’m also going to explain the key Kubernetes concepts that you need to know to understand how all these pieces together. This is a long one, buckle up.

Creating Your Cluster

In my last blog post, I showed you how to create a three-node Kubernetes on premise, virtual machine based cluster. I’m going to use the same setup for this blog post. Check out how to create this cluster at this link here. There’s a reason I wrote that post first :)

Process Overview

Here’s the big picture of all the steps we will perform in this demonstration

  • Create a Namespace
  • Create Secrets
  • Create a Storage Class and mark it default
  • Create Persistent Volumes
  • Create a ServiceAccount, ClusterRole, ClusterRoleBinding and a Deployment
  • Deploy the SQL Server Pods
  • Expose the Availability Group Services as a Kubernetes Service
  • Connect to our Availability Group from outside our cluster
  • Create a database
I’m going to be running these commands from the Cluster Master, you can run these from any host that can talk to your API Server. We’re going to execute the first few commands using kubectl directly then we’re going to switch to loading our configurations from “deployment manifests” which describe our configuration in YAML files and in this case, describe the Availability Group Deployment.

Create a Namespace

First up, we’ll create a Namespace. In Kubernetes you can use namespaces to put boundaries around resources for organizational or security reasons.  

demo@k8s-master1:~/ag$ kubectl create namespace ag1

namespace/ag1 created


demo@k8s-master1:~/ag$ kubectl get namespaces

NAME          STATUS   AGE

ag1           Active   11m

default       Active   28h

kube-public   Active   28h

kube-system   Active   28h

Create Secrets

In Kubernetes, the cluster store can hold Secrets…in other words sensitive data like passwords. This is valuable because we don’t want to store this information in our containers and we certainly don’t want to have our passwords as clear text in our deployment manifests. So in those manifests, we can reference these values and then upon deployment the Pods will retrieve the secrets when they’re started and pass the secret into the container for the application to use. In this case, we’re creating two secrets to be used by our Pods. The first is the SA password we’ll use for our SQL Server Instance, the second is the password for our Service Master Key which is behind the certificates that are used to authenticate the Availability Group (*cough*) Database Mirroring endpoints.

Let’s create the secrets with kubectl.

demo@k8s-master1:~/ag$ kubectl create secret generic sql-secrets –from-literal=sapassword=”1-S0methingS@Str0ng” –from-literal=masterkeypassword=”2-S0methingS@Str0ng”  –namespace ag1

secret/sql-secrets created

 
Want to know how to read a secret out of the cluster store?
 
Well here you go, just change the masterkeypassword string to the name of the secret you want to decode. 
 

demo@k8s-master1:~/ag$ kubectl get secret sql-secrets -o yaml –namespace ag1 | grep masterkeypassword  | awk ‘{ print $2 }’ | base64 –decode 

2-S0methingS@Str0ng
demo@k8s-master1:~/ag
 

Create a Storage Class and Mark it Default

OK, now it’s time to work on our storage configuration. This is where we’re going to deviate most from the Microsoft documentation. We’re going to start off by creating a StorageClass. A StorageClass is a way to group storage together based on the storage’s attributes. In this case, we’re going to use a StorageClass because later on in the YAML files provided by Microsoft they are going to make storage requests of the cluster referencing the default storage class in the namespace. So that’s what this code does, creates the local-storage StorageClass and marks it as default.

Here is the YAML definition of our StorageClass, save this into a file called StorageClass.yaml.

File 1 – StorageClass.yaml

Once you have that code saved into StorageClass.yaml, go ahead and run the following command to pass the StorageClass manifest to the API server for it to create the resource for you.

demo@k8s-master1:~/ag$ kubectl apply -f StorageClass.yaml –namespace ag1

storageclass.storage.k8s.io/local-storage created
 

demo@k8s-master1:~/ag$ kubectl get storageclass –namespace ag1

NAME                      PROVISIONER                    AGE

local-storage (default)   kubernetes.io/no-provisioner   3h20m

Create Persistent Volumes

Next up is creating our actual storage. In Kubernetes, the cluster provides storage to Pods and the Pods request the storage. Cluster storage can be many different types. You can have NFS, virtual disks from your cloud provider, local storage and many more. Local storage is the storage that’s attached to the Kubernetes Node itself. In this demonstration, we’re going to use local storage. Since we’re deploying Availability Groups that will put a Pod on each Node in our cluster, we’re going to need to define three PersistentVolumes, one on each Node.. Looking at the code in File 2 – PV.yaml (below) you will see three PersistentVolumes each with a different name, all pointing to /var/opt/mssql. This will be local on each Node in our cluster. So we will need to make a /var/opt/mssql directory on each node in our cluster. So go ahead and do that now. Storage in HA systems requires understanding of what data is living where in your system and layering the appropriate data protections to meet your recovery objectives. This configuration places the storage on each Node in your Kubernetes Cluster. For more information on the local storage type in Kubernetes check out this post here. In that post they specifically call out that this Persistent Volume type is appropriate for “Distributed storage systems that shard or replicate data across multiple nodes” and Availability Groups fall into that category.

In an effort to loosely couple Pods and their storage, the cluster administrator defines Persistent Volumes, that what you’ll do when you run the code in File 2 – PV.yaml below. Then the pods will use PersistentVolumeClaim to attach the Pods to the PersistentVolumes.

File 2 – PV.yaml

Once you have that code saved into PV.yaml, go ahead and run the following command to pass the PersistentVolume manifest to the API server for it to create the resource for you.

demo@k8s-master1:~/ag$ kubectl apply -f pv.yaml –namespace ag1

persistentvolume/ag1-pv-volume-node1 created

persistentvolume/ag1-pv-volume-node2 created

persistentvolume/ag1-pv-volume-node3 created


demo@k8s-master1:~/ag$ kubectl get PersistentVolume –namespace ag1

NAME                  CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM   STORAGECLASS    REASON   AGE

ag1-pv-volume-node1   10Gi       RWO            Retain           Available           local-storage            29s

ag1-pv-volume-node2   10Gi       RWO            Retain           Available           local-storage            29s

ag1-pv-volume-node3   10Gi       RWO            Retain           Available           local-storage            29s

Create a ServiceAccount, ClusterRole, ClusterRoleBinding and a Deployment

Now that we have our storage created it’s time to get started creating our resources for our cluster. In the Samples provided by Microsoft, they provide operator.yaml. For our deployment, we’ll use that file just as is from Microsoft. I have the contents below for you. The core details of the operator.yaml manifest file are that it creates a ServiceAccount, a ClusterRole, a ClusterRoleBinding and also defines the Deployment for the Kubernetes Operator Pod for our Availability Group. Basically, this sets up the security contexts in the cluster for our Pods and also kicks off the Deployment of the Availability Group Kubernetes Operator Pod. A Deployment is a Kubernetes object that will ensure that the defined Pod is up and running at all times. Looking towards the bottom of the file you’ll see replicas: 1 this defines that there must be exactly one Operator pod using the 2019-CTP2.1-ubuntu container at all times. 

File 3 – operator.yaml 

Now let’s go ahead and deploy operator.yaml and create the resources. 

demo@k8s-master1:~/ag$ kubectl apply -f operator.yaml –namespace ag1

Warning: kubectl apply should be used on resource created by either kubectl create –save-config or kubectl apply

namespace/ag1 configured

serviceaccount/mssql-operator created

clusterrole.rbac.authorization.k8s.io/mssql-operator-ag1 created

clusterrolebinding.rbac.authorization.k8s.io/mssql-operator-ag1 created

deployment.apps/mssql-operator created

 
If you want to inspect the resources further here are some commands to do that. I’ll leave this as an exercise for the reader.
 

kubectl get ServiceAccount –namespace ag1

kubectl describe ClusterRole mssql-operator-ag1  –namespace ag1

kubectl describe ClusterRoleBinding mssql-operator-ag1  –namespace ag1

kubectl get deployment –namespace ag1

kubectl describe deployment –namespace ag1 

Before moving on, we’ll want to make sure our Deployment is finished and Ready. We can use kubectl get deployment for that, the key here is the DESIRED and CURRENT are both 1. This means our Operator is online and ready.

demo@k8s-master1:~/ag$ kubectl get deployment –namespace ag1

NAME             DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE

mssql-operator   1         1         1            1           4m38s


If you want to double check that, you can make sure your Pods online with kubectl get pods. There you can see the operator Pod’s Status is Running.
 

demo@k8s-master1:~/ag$ kubectl get pods –namespace ag1

NAME                              READY   STATUS    RESTARTS   AGE

mssql-operator-6d88564d97-hqz8r   1/1     Running   0          7m8s

Deploy the SQL Server Pods

Ok, now that the Storage, Security and the Operator are deployed. Now it’s time to deploy the Pods for our SQL Server Availability Group Replicas. In File 3 – sqlserver.yaml (below) we define the resources needed to get our Pods up and running. But, this file is a little bit different…it’s using Custom Resources. Your first hint to that is look at the apiVersion, it references mssql.microsoft.com/v1 and the kind: SqlServer. Microsoft has chosen to implement a custom object likely so that it can abstract away some of the complexity of creating this configuration. 

In this file, you are going to see a lot of things come together from the other configurations we’ve made so far in this post. You’ll find that the ag1 namespace is referenced, you’ll see the storageClass is default, and the saPassword being read from the Cluster’s secrets.

In addition to the custom SqlServer resource, in this file, you will also find the Service object defined for each Pod replica. The Service provides persistent access to the Pod’s application. In this file, we create three services all on 1433. This port is the port listening on the cluster network. 

I did make one change to this file from the original Microsoft file. I changed the Service Type from LoadBalancer to NodePort. Doing this exposes the Service which is running on 1433 inside the Pod and also on the Pod network to the Node’s real IP address and bind the Pods internal 1433 port to an available ephemeral port on the Node. This means I can connect to each of the SQL Instances outside of the Kubernetes cluster using the IP address of the virtual machine (Node) and the NodePort ephemeral port. The type LoadBalancer is used in cloud scenarios where the cloud provider stands up and load balancer resource for you. We’re doing this On-Prem, so this had to change.

File 3 – sqlserver.yaml

Let’s now deploy this Pods and Services by passing sqlserver.yaml into our API Server. This might take a minute or two as the containers are downloaded from the Internet and started. In the output below you can see the three Pods are Created and the three services are created. I do want to call out when you create the Pods, you will see 6 Pods when you use the kubectl get pods command. The “initialize” Pods are managed by the Deployment as Kubernetes Jobs that are used to configure the Availability Group Replicas, these run only once and complete. When running the deployment, a successful deployment will have three mssqlN-0 Pods up with a status of Running and the  initialize pods are Completed.

demo@k8s-master1:~/ag$ kubectl apply -f sqlserver.yaml –namespace ag1

sqlserver.mssql.microsoft.com/mssql1 created

service/mssql1 created

sqlserver.mssql.microsoft.com/mssql2 created

service/mssql2 created

sqlserver.mssql.microsoft.com/mssql3 created

service/mssql3 created
 

demo@k8s-master1:~/ag$ kubectl get pods –namespace ag1

NAME                              READY   STATUS      RESTARTS   AGE

mssql-initialize-mssql1-klhzh     0/1     Completed   0          7m

mssql-initialize-mssql2-8vd6r     0/1     Completed   0          6m57s

mssql-initialize-mssql3-4tjvd     0/1     Completed   0          6m54s

mssql-operator-6d88564d97-hqz8r   1/1     Running     0          30m

mssql1-0                          2/2     Running     0          7m

mssql2-0                          2/2     Running     0          6m58s

mssql3-0                          2/2     Running     0          6m55s

If you want to get a peek at what’s been written to standard out in a Pod you can use kubectl logs. Let’s do that for one of the initialize Pods above to see what they did for us. In the output below you can see it’s the job of the initialize container to configure the Availability Group on the Pod that’s running our AG Replica on that same Node. There’s an initialize Pod for each replica on each Node.

demo@k8s-master1:~/ag$ kubectl logs mssql-initialize-mssql1-klhzh –namespace ag1

2018/11/13 02:26:14 Using randomly generated master key password

2018/11/13 02:26:14 Statefulset has 1 replicas but could only find 0

Found pod [mssql1-0] with owner [7d5ef98d-e6eb-11e8-816e-000c296ac327]2018/11/13 02:26:15 [192.168.3.5] Setting sa pasword…

ERROR: 2018/11/13 02:26:15 [192.168.3.5] Could not connect: Unresponsive or down Unable to open tcp connection with host ‘192.168.3.5:1433’: dial tcp 192.168.3.5:1433:

…output omitted…

ERROR: 2018/11/13 02:26:28 [192.168.3.5] Could not connect: Unresponsive or down Unable to open tcp connection with host ‘192.168.3.5:1433’: dial tcp 192.168.3.5:1433: getsockopt: connection refused

ERROR: 2018/11/13 02:26:28 [192.168.3.5] Both old and new sa password failed

ERROR: 2018/11/13 02:26:29 [192.168.3.5] Could not connect: Unresponsive or down Login error: mssql: Login failed for user ‘sa’.

ERROR: 2018/11/13 02:26:29 [192.168.3.5] Could not connect: Unresponsive or down Login error: mssql: Login failed for user ‘sa’.

ERROR: 2018/11/13 02:26:29 [192.168.3.5] Both old and new sa password failed

ERROR: 2018/11/13 02:26:30 [192.168.3.5] Could not connect: Unresponsive or down Login error: mssql: Login failed for user ‘sa’.

2018/11/13 02:26:31 [192.168.3.5] sa password updated

2018/11/13 02:26:31 [192.168.3.5] Creating master key

2018/11/13 02:26:31 [192.168.3.5] Creating sql login dbm-mssql1 if it does not already exist

2018/11/13 02:26:31 [192.168.3.5] Creating sql user dbm-mssql1 if it does not already exist

2018/11/13 02:26:31 [192.168.3.5] Granting dbm-mssql1 availability group permissions

2018/11/13 02:26:31 [192.168.3.5] Granting dbm-mssql1 control to the database mirroring endpoint, dbm, to if it already exists

2018/11/13 02:26:31 [192.168.3.5] Granting  dbm-mssql1 control to the certificates used on the database mirroring endpoint, dbm

2018/11/13 02:26:31 [192.168.3.5] Granting dbm-mssql1 control to availibility group ag1

2018/11/13 02:26:31 Updating secret to note that the initialization is complete

2018/11/13 02:26:31 Uploading cert secret for local instance…

2018/11/13 02:26:31 Initialization complete

 
Here’s some more commands for you to further investigate the Availability Group’s Kubernetes Configuration. Poke around in there and see what’s up. 
 

demo@k8s-master1:~/ag$ kubectl describe pods  -n ag1

demo@k8s-master1:~/ag$ kubectl describe statefulset –namespace ag1

 

Expose the Availability Group Services as a Service

Ok, so we’ve created the AG Replicas in our Kubernetes Cluster. Now it’s time to create a Kubernetes Service for access to the Primary and Read Only Read-only Replicas. Kubernetes handles networking for us. It’s responsible for adding persistency to the ephemeral container world. So these services are going to be our application’s primary access points to connect to the SQL Server. For our On-Prem scenario, we’re going to deviate from Microsoft’s documentation, similar to what we had to do when we exposed each individual replica as a Service. In the ag-services.yaml file provided in the Microsoft examples, the AG Services are Type LoadBalancer. This is Service type is used in cloud scenarios and we don’t have a that in our On-Prem configuration. So we’re going to change this again to NodePort. The reason I’m choosing NodePort here is to expose the service outside the cluster. This way I will be able to use my own tools to access the SQL Instance from outside the cluster.

Here’s the code for our ag-services.yaml Services manifest.
File 4 – ag-services.yaml

Now let’s apply that manifest to create our AG Services in our cluster.  

demo@k8s-master1:~/ag$ kubectl apply -f ag-services.yaml –namespace ag1

service/ag1-primary created

service/ag1-secondary created


And take a quick peek at our Service configuration. You’ll see we don’t have an External-IP as described in Microsoft walk-through. This would come from our LoadBalancer. Since we’re using NodePort, our IP address will be that of the actual Nodes. 

demo@k8s-master1:~/ag$ kubectl get service –namespace ag1

NAME            TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)             AGE

ag1             ClusterIP   None             <none>        1433/TCP,5022/TCP   9h

ag1-primary     NodePort    10.110.116.77    <none>        1433:30625/TCP      2m6s

ag1-secondary   NodePort    10.100.132.228   <none>        1433:30380/TCP      2m6s

mssql1          NodePort    10.103.126.32    <none>        1433:32572/TCP      9h

mssql2          NodePort    10.102.175.227   <none>        1433:30001/TCP      9h

mssql3          NodePort    10.107.215.217   <none>        1433:31539/TCP      9h


What IP and Port do we connect our applications to for the Availability Group Primary Replica? For the IP address, it’s the real address of the Node, in other words the actual IP address of your virtual machine. For the port, well, let’s use kubectl describe for that. Here you can see the NodePort is 30625. The port is allocated by the cluster, yours will vary from this as this can be any port in the ephemeral port range. We can point our applications to any node in our cluster on THAT port and the cluster will redirect the traffic to the correct Node internal. So for me, it’s k8s-master1:30625.

demo@k8s-master1:~/ag$ kubectl describe service  ag1-primary -n ag1

Name:                     ag1-primary

Namespace:                ag1

Labels:                   <none>

Annotations:              kubectl.kubernetes.io/last-applied-configuration:

                            {“apiVersion”:”v1″,”kind”:”Service”,”metadata”:{“annotations”:{},”name”:”ag1-primary”,”namespace”:”ag1″},”spec”:{“ports”:[{“name”:”tds”,”p…

Selector:                 role.ag.mssql.microsoft.com/ag1=primary,type=sqlservr

Type:                     NodePort

IP:                       10.110.116.77

Port:                     tds  1433/TCP

TargetPort:               1433/TCP

NodePort:                 tds  30625/TCP

Endpoints:                192.168.3.5:1433

Session Affinity:         None

External Traffic Policy:  Cluster

Events:                   <none>


Let’s use sqlcmd to test external connectivity to our SQL Instance. The first one we will connect to k8s-master1 on Port 30625, the second we’ll connect to k8s-node1’s IP address (remember that’s coming from DHCP so you’ll have to go get if for your network) on port 30625. In the output below you can see we always hit the primary replica for our AG, mssql1-0. To use the name k8s-master1, I have an entry in my local hosts file to resolve the name to the IP of the server. You may want to do the same.

Anthonys-MacBook-Pro:~ aen$ sqlcmd -S k8s-master1,30625 -Q “SELECT @@SERVERNAME” -U sa -p

Password: 

                                                                                                                                

——————————————————————————————————————————–

mssql1-0                                                                                                                        

 

(1 rows affected)

 

Network packet size (bytes): 4096

1 xact[s]:

Clock Time (ms.): total         2  avg   2.0 (500.0 xacts per sec.)


Anthonys-MacBook-Pro:~ aen$ sqlcmd -S 172.16.94.136,30625 -Q “SELECT @@SERVERNAME” -U sa -p

Password: 

                                                                                                                                

——————————————————————————————————————————–

mssql1-0                                                                                                                        

 

(1 rows affected)

 

Network packet size (bytes): 4096

1 xact[s]:

Clock Time (ms.): total         1  avg   1.0 (1000.0 xacts per sec.)

In figure 1, you can find the connection information to connect to our AG primary with Azure Data Studio. Remember, I have that host name in a host file. So create that entry if you need one.

NewImage

Figure 1 – Connection Parameters for Azure Data Studio

Create an Availability Group Database

Now with everything up and running, let’s create an Availability Group database. We’re going to depend on direct seeding to copy the database to each Replica in our Availability Group, pretty nice feature, eh? Take the text below and use sqlcmd  or Azure Data Studio to create the database, Hey, in the code below, see how I’m backing up to nul, yea if this is a real database…that’s a bad idea. I’m just doing that to get the database ready to be added to the AG.
Listing 5 – Create your Availability Group Database
 
Now let’s check the status of our AG configuration with Azure Data Studio. Here’s the query to pull the AG configuration information:
Query 1 – Availability Group Configuration Query
 
 
NewImage
 
Figure 2 – Availability Group Configuration 
 
One thing that’s interesting to call out in this output in Figure 2 is you see the endpoint_url is on the 192.168.x.y network. This is the Pod network. Remember way back when we created our cluster together in my previous blog post, we needed to ensure that our Pods have the ability to communicate with each other…so we deployed the Calico Pod network. The network range on that what 192.168.0.0/16. That’s this network, our Pods’ network.

Wrap up

If you want to get a peek at all the resources you created today, use the following. This will generate this output for you to look at your configuration.
 

demo@k8s-master1:~/ag$ kubectl get all –namespace ag1

NAME                                  READY   STATUS      RESTARTS   AGE

pod/mssql-initialize-mssql1-klhzh     0/1     Completed   0          12h

pod/mssql-initialize-mssql2-8vd6r     0/1     Completed   0          12h

pod/mssql-initialize-mssql3-4tjvd     0/1     Completed   0          12h

pod/mssql-operator-6d88564d97-hqz8r   1/1     Running     0          12h

pod/mssql1-0                          2/2     Running     0          12h

pod/mssql2-0                          2/2     Running     0          12h

pod/mssql3-0                          2/2     Running     0          12h

 

NAME                    TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)             AGE

service/ag1             ClusterIP   None             <none>        1433/TCP,5022/TCP   12h

service/ag1-primary     NodePort    10.110.116.77    <none>        1433:30625/TCP      176m

service/ag1-secondary   NodePort    10.100.132.228   <none>        1433:30380/TCP      176m

service/mssql1          NodePort    10.103.126.32    <none>        1433:32572/TCP      12h

service/mssql2          NodePort    10.102.175.227   <none>        1433:30001/TCP      12h

service/mssql3          NodePort    10.107.215.217   <none>        1433:31539/TCP      12h

 

NAME                             DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE

deployment.apps/mssql-operator   1         1         1            1           12h

 

NAME                                        DESIRED   CURRENT   READY   AGE

replicaset.apps/mssql-operator-6d88564d97   1         1         1       12h

 

NAME                      DESIRED   CURRENT   AGE

statefulset.apps/mssql1   1         1         12h

statefulset.apps/mssql2   1         1         12h

statefulset.apps/mssql3   1         1         12h

 

NAME                                COMPLETIONS   DURATION   AGE

job.batch/mssql-initialize-mssql1   1/1           19s        12h

job.batch/mssql-initialize-mssql2   1/1           18s        12h

job.batch/mssql-initialize-mssql3   1/1           17s        12h


 Want to dump your entire configuration to yaml, use this
 

kubectl get all –namespace ag1 -o yaml

 
Well, I hope you enjoyed this lengthy walkthrough on how to create a SQL Server Always On Availability Group using On-Premises virtual machines. I tried to do two things with this post, first show you how to set this up, and second introduce the SQL Server pro to core Kubernetes constructs.

Please feel free to contact me with any questions regarding Linux, Kubernetes or other SQL Server related issues at : aen@centinosystems.com


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