Running a Minecraft Server in Azure Container Instances

All of my children are big fans of Minecraft, and recently my son asked me to help him set up a Minecraft server so he could play online with his friends. Obviously, one option would have been to create a Virtual Machine and install the Minecraft server on that. However, that's quite an expensive option - at about £30 a month for a virtual machine that would sit idle for most of the time.

Now of course in Azure a VM can be put into a "stopped deallocated" state, during which you are not charged for compute. But when you restart the VM, you have a bit of a wait for boot-up, and it will have a different IP address, which my son would then need to communicate to all his friends.

And this is actually a great use case for Azure Container Instances. We can simply ask Azure to spin up a container running the Minecraft server (using a Minecraft server image from Docker Hub), use it, and stop it when we've finished. ACI containers start and stop quickly, and we can assign them a friendly domain name that will remain the same when we start up again. And so long as we map the data folder to an Azure Storage File Share, all the state stored on the server will be persisted while our container is not running. This keeps our costs to a minimum.

In this post, I'll show you how we can automate the creation of all the infrastructure we need with the Azure Az PowerShell module. Normally my preference would be to do this with the Azure CLI, but I'm opting to do this all with the PowerShell module, for reasons I'll explain in a bit.

Get started with Az PowerShell

First, if like me you're fairly new to the Az PowerShell module, here's the basic commands you'll need to get logged in, select your subscription, and explore your resource groups:

# login to Azure PowerShell
Connect-AzAccount

# see what subscriptions are available
Get-AzContext -ListAvailable

# to see the current subscription name
$azContext = Get-AzContext
$azContext.Subscription.Name

# select the subscription we want to use
Set-AzContext -SubscriptionName "My Azure Subscription"

# see what resource groups we have
Get-AzResourceGroup | select ResourceGroupName

Now, let's create a Resource Group to hold the resources we'll create in this demo with New-AzResourceGroup:

# create a resource group
$resourceGroupName = "MinecraftTest"
$location = "westeurope"
New-AzResourceGroup -Name $resourceGroupName -Location $location

Creating a Storage Account and File Share

To ensure that we can persist the state of the server, we need to create Storage Account and a file share within that Storage Account. I've created a PowerShell function called SetupStorage which uses New-AzStorageAccount to create a Storage Account and New-AzStorageShare to create a file share. I wanted this function to be idempotent and not fail if the Storage Account and share already existed, and the way I did that was to use the Get- methods first, with the -ErrorAction SilentlyContinue flag set.

Once we've ensured that the Storage Account and the file share are present, we need to get hold of the Storage Account key with Get-AzStorageAccountKey and turn that into a PSCredential object which we'll need to mount the share as a volume on our container.

function SetupStorage {
    param( [string]$StorageResourceGroupName, 
           [string]$StorageAccountName, 
           [string]$ShareName,
           [string]$Location)

    # check if storage account exists
    $storageAccount = Get-AzStorageAccount `
        -ResourceGroupName $StorageResourceGroupName `
        -Name $StorageAccountName `
        -ErrorAction SilentlyContinue

    if ($storageAccount -eq $null) {
        # create the storage account
        $storageAccount = New-AzStorageAccount `
            -ResourceGroupName $StorageResourceGroupName `
            -Name $StorageAccountName `
            -SkuName Standard_LRS `
            -Location $Location
    }

    # check if the file share already exists
    $share = Get-AzStorageShare `
        -Name $ShareName -Context $storageAccount.Context `
        -ErrorAction SilentlyContinue

    if ($share -eq $null) {
        # create the share
        $share = New-AzStorageShare `
            -Name $ShareName `
            -Context $storageAccount.Context
    }

    # get the credentials
    $storageAccountKeys = Get-AzStorageAccountKey `
        -ResourceGroupName $StorageResourceGroupName `
        -Name $StorageAccountName

    $storageAccountKey = $storageAccountKeys[0].Value
    $storageAccountKeySecureString = ConvertTo-SecureString $storageAccountKey -AsPlainText -Force
    $storageAccountCredentials = New-Object System.Management.Automation.PSCredential ($storageAccountName, $storageAccountKeySecureString)
    
    return $storageAccountCredentials
}

Now we have the SetupStorage function, let's pick a name for the Storage Account and file share and get hold of the credentials.

$storageAccountName = "minecraft20190514" # must be unique across azure
$shareName = "minecraft"
$storageAccountCredentials = SetupStorage `
    -StorageResourceGroupName $resourceGroupName `
    -StorageAccountName $storageAccountName `
    -ShareName $shareName `
    -Location $location

Creating an ACI Container Group

Now we're ready to create the container group that will run the Minecraft server. First we need to pick a name for the container group and a unique DNS name prefix to give our Minecraft server a friendly DNS name. We also need to set up some environment variables - one to accept the EULA, and one to set a particular Minecraft user as the admin for this server (this will get written into the ops.json file in the file share the first time this container starts up).

We can create the container group with New-AzContainerGroup and the DOcker image we're using is itzg/minecraft-server from Docker Hub which is a well maintained Minecraft server image with options to configure Bukkit and Spigot (not claiming to know what they are, but my kids tell me they're good!). I need to ensure the container group has a public IP address, and mounts the file share to the /data path. We also need to open the default Minecraft server port of 25565.

$containerGroupName = "minecraft20190514"
$dnsNameLabel = "minecrafttest"
$environmentVariables = @{ EULA = "TRUE"; OPS = "YourMinecraftUserName";
}

New-AzContainerGroup -ResourceGroupName $resourceGroupName `
    -Name $containerGroupName `
    -Image "itzg/minecraft-server" `
    -AzureFileVolumeAccountCredential $storageAccountCredentials `
    -AzureFileVolumeShareName $shareName `
    -AzureFileVolumeMountPath "/data" `
    -IpAddressType Public `
    -OsType Linux `
    -DnsNameLabel $dnsNameLabel `
    -Port 25565 `
    -EnvironmentVariable $environmentVariables

And with that one command, our Minecraft server will be up and running. It will start up very quickly, and we can check up on its status with Get-AzContainerGroup which will tell us the fully qualified domain name of the server.

# check up on the status
$containerGroup = Get-AzContainerGroup -ResourceGroupName $resourceGroupName -Name $containerGroupName

# view the domain name (e.g. minecrafttest.westeurope.azurecontainer.io)
$containerGroup.Fqdn

Starting and stopping the container group

I was hoping that the PowerShell Az module would have a nice and simple command to start and stop container groups like you can with the Azure CLI's az container stop and az container start commands. Unfortunately equivalent commands haven't been created for the Azure Az PowerShell module yet (please vote for my feature request here).

How can we start and stop the container without built-in commands? Well, we can call the Azure REST API's directly, such as this API to stop a container group. However, we need to provide a bearer token, and this turned out to be a challenge to get hold of. After a bit of experimenting, I found that the following code could get me a valid bearer token I could use to call the Azure REST API.

function Get-AccessToken($tenantId) {
    $azureRmProfile = [Microsoft.Azure.Commands.Common.Authentication.Abstractions.AzureRmProfileProvider]::Instance.Profile;
    $profileClient = New-Object Microsoft.Azure.Commands.ResourceManager.Common.RMProfileClient($azureRmProfile);
    $profileClient.AcquireAccessToken($tenantId).AccessToken;
}

With that in place, we can define a Send-ContainerGroupCommand function that can call any of the start, stop, and restart endpoints for container groups:

function Send-ContainerGroupCommand($resourceGroupName, $containerGroupName, $command) {
    $azContext = Get-AzContext
    $subscriptionId = $azContext.Subscription.Id
    $commandUri = "https://management.azure.com/subscriptions/$subscriptionId/resourceGroups/$resourceGroupName/providers/Microsoft.ContainerInstance/containerGroups/$containerGroupName/$command" + "?api-version=2018-10-01"
    $accessToken = Get-AccessToken $azContext.Tenant.TenantId
    $response = Invoke-RestMethod -Method Post -Uri $commandUri -Headers @{ Authorization="Bearer $accessToken" }
    $response
}

And then creating our own helper functions to stop and start container groups becomes easy:

function Stop-ContainerGroup($resourceGroupName, $containerGroupName) {
    Send-ContainerGroupCommand $resourceGroupName $containerGroupName  "stop"
}

function Start-ContainerGroup($resourceGroupName, $containerGroupName) {
    Send-ContainerGroupCommand $resourceGroupName $containerGroupName "start"
}

function Restart-ContainerGroup($resourceGroupName, $containerGroupName) {
    Send-ContainerGroupCommand $resourceGroupName $containerGroupName "restart"
}

So now I can stop the Minecraft server we just created with this command:

Stop-ContainerGroup $resourceGroupName $containerGroupName

The great thing about this is that we are no longer paying anything for our container group - they are free while in the stopped state. The only cost is associated with what's in the file share. And when we restart the container group, it will come back up with the same domain name. This is great to allow my children to share the address of the server with their friends, which can remain constant. In fact, I was able to map a custom domain with a DNS CNAME record to the container group's domain name to make the server address even easier to share.

Summary and what's next?

In this post we saw how to fully automate the creation of a Minecraft server running in Azure Container Instances, along with a file share that can persist the server data. But obviously whenever my children want to start the server, they need me to connect to Azure PowerShell and run the start command. And I also need to remember to stop the server at the end of the gaming session or I'll end up with an unexpectedly high bill.

So what would be great next is to automate the process, so I can give my children a way to start the server themselves, that doesn't require them to have access to my Azure subscription, and also a way to automatically shut it down after a certain elapsed duration.

Now that Azure Functions v2 supports PowerShell functions, and integrates directly with the Az Module, it's an obvious choice for the automation. So I'm hoping to follow on with another post soon showing how we can create a PowerShell Azure Functions App to automate the starting and stopping of the Minecraft container.