Run a Linux VM on Azure

This reference architecture shows a set of proven practices for running a Linux virtual machine (VM) on Azure. It includes recommendations for provisioning the VM along with networking and storage components. This architecture can be used to run a single instance, and is the basis for more complex architectures such as n-tier applications. Deploy this solution.

[0]

Architecture

Provisioning a VM in Azure involves more moving parts than just the VM itself. There are compute, networking, and storage elements that you need to consider.

  • Resource group. A resource group is a container that holds related resources. You usually create resource groups for different resources in a solution based on their lifetime, and who will manage the resources. For a single VM workload, you may create a single resource group for all resources.
  • VM. Azure supports running various popular Linux distributions, including CentOS, Debian, Red Hat Enterprise, Ubuntu, and FreeBSD. For more information, see Azure and Linux. You can provision a VM from a list of published images or from a virtual hard disk (VHD) file that you upload to Azure Blob storage.
  • OS disk. The OS disk is a VHD stored in Azure Storage. That means it persists even if the host machine goes down. The OS disk is /dev/sda1.
  • Temporary disk. The VM is created with a temporary disk. This disk is stored on a physical drive on the host machine. It is not saved in Azure Storage and might be deleted during reboots and other VM lifecycle events. Use this disk only for temporary data, such as page or swap files. The temporary disk is /dev/sdb1 and is mounted at /mnt/resource or /mnt.
  • Data disks. A data disk is a persistent VHD used for application data. Data disks are stored in Azure Storage, like the OS disk.
  • Virtual network (VNet) and subnet. Every VM in Azure is deployed into a VNet that is further divided into subnets.
  • Public IP address. A public IP address is needed to communicate with the VM — for example, via SSH.
  • Network interface (NIC). The NIC enables the VM to communicate with the virtual network.
  • Network security group (NSG). The NSG is used to allow/deny network traffic to the subnet. You can associate an NSG with an individual NIC or with a subnet. If you associate it with a subnet, the NSG rules apply to all VMs in that subnet.
  • Diagnostics. Diagnostic logging is crucial for managing and troubleshooting the VM.

You can download a Visio file of this architecture.

Note

Azure has two different deployment models: Resource Manager and classic. This article uses Resource Manager, which Microsoft recommends for new deployments.

Recommendations

This architecture shows the baseline recommendations for running a Linux VM in Azure. However, we don't recommend using a single VM for mission critical workloads because it creates a single point of failure. For higher availability, deploy multiple VMs in an availability set. For more information, see Running multiple VMs on Azure.

VM recommendations

Azure offers many different virtual machine sizes, but we recommend the DS- and GS-series because these machine sizes support Premium Storage. Select one of these machine sizes unless you have a specialized workload such as high-performance computing. For details, see virtual machine sizes.

If you are moving an existing workload to Azure, start with the VM size that's the closest match to your on-premises servers. Then measure the performance of your actual workload with respect to CPU, memory, and disk input/output operations per second (IOPS), and adjust the size if needed. If you require multiple NICs for your VM, be aware that the maximum number of NICs is a function of the VM size.

When you provision the VM and other resources, you must specify a region. Generally, choose a region closest to your internal users or customers. However, not all VM sizes may be available in all region. For details, see Services by region. To list the VM sizes available in a specific region, run the following Azure command-line interface (CLI) command:

az vm list-sizes --location <location>

For information about choosing a published VM image, see Select Linux VM images with the Azure CLI.

Enable monitoring and diagnostics, including basic health metrics, diagnostics infrastructure logs, and boot diagnostics. Boot diagnostics can help you diagnose boot failure if your VM gets into a non-bootable state. For more information, see Enable monitoring and diagnostics.

The following CLI command enables diagnostics:

az vm diagnostics set <resource-group> <vm-name>

The following CLI command enables boot diagnostics:

az vm boot-diagnostics enable <resource-group> <vm-name>

Disk and storage recommendations

For best disk I/O performance, we recommend Premium Storage, which stores data on solid-state drives (SSDs). Cost is based on the size of the provisioned disk. IOPS and throughput (that is, data transfer rate) also depend on disk size, so when you provision a disk, consider all three factors (capacity, IOPS, and throughput).

We also recommend the use of managed disks. Managed disks do not require a storage account. You simply specify the size and type of disk and it is deployed in a highly available way.

If you are not using managed disks, create separate Azure storage accounts for each VM to hold the virtual hard disks (VHDs) in order to avoid hitting the IOPS limits for storage accounts.

Add one or more data disks. When you create a VHD, it is unformatted. Log in to the VM to format the disk. In the Linux shell, data disks are displayed as /dev/sdc, /dev/sdd, and so on. You can run lsblk to list the block devices, including the disks. To use a data disk, create a partition and file system, and mount the disk. For example:

# Create a partition.
sudo fdisk /dev/sdc     # Enter 'n' to partition, 'w' to write the change.

# Create a file system.
sudo mkfs -t ext3 /dev/sdc1

# Mount the drive.
sudo mkdir /data1
sudo mount /dev/sdc1 /data1

If you are not using managed disks and have a large number of data disks, be aware of the total I/O limits of the storage account. For more information, see virtual machine disk limits.

When you add a data disk, a logical unit number (LUN) ID is assigned to the disk. Optionally, you can specify the LUN ID — for example, if you're replacing a disk and want to retain the same LUN ID, or you have an application that looks for a specific LUN ID. However, remember that LUN IDs must be unique for each disk.

You may want to change the I/O scheduler to optimize for performance on SSDs because the disks for VMs with premium storage accounts are SSDs. A common recommendation is to use the NOOP scheduler for SSDs, but you should use a tool such as iostat to monitor disk I/O performance for your workload.

For best performance, create a separate storage account to hold diagnostic logs. A standard locally redundant storage (LRS) account is sufficient for diagnostic logs.

Network recommendations

The public IP address can be dynamic or static. The default is dynamic.

All NSGs contain a set of default rules, including a rule that blocks all inbound Internet traffic. The default rules cannot be deleted, but other rules can override them. To enable Internet traffic, create rules that allow inbound traffic to specific ports — for example, port 80 for HTTP.

To enable SSH, add a rule to the NSG that allows inbound traffic to TCP port 22.

Scalability considerations

You can scale a VM up or down by changing the VM size. To scale out horizontally, put two or more VMs behind a load balancer. For details, see Running multiple VMs on Azure for scalability and availability.

Availability considerations

For higher availability, deploy multiple VMs in an availability set. This also provides a higher service level agreement (SLA).

Your VM may be affected by planned maintenance or unplanned maintenance. You can use VM reboot logs to determine whether a VM reboot was caused by planned maintenance.

VHDs are stored in Azure storage, and Azure storage is replicated for durability and availability.

To protect against accidental data loss during normal operations (for example, because of user error), you should also implement point-in-time backups, using blob snapshots or another tool.

Manageability considerations

Resource groups. Put tightly coupled resources that share the same life cycle into the same resource group. Resource groups allow you to deploy and monitor resources as a group, and roll up billing costs by resource group. You can also delete resources as a set, which is very useful for test deployments. Give resources meaningful names. That makes it easier to locate a specific resource and understand its role. See Recommended Naming Conventions for Azure Resources.

SSH. Before you create a Linux VM, generate a 2048-bit RSA public-private key pair. Use the public key file when you create the VM. For more information, see How to Use SSH with Linux and Mac on Azure.

Stopping a VM. Azure makes a distinction between "stopped" and "deallocated" states. You are charged when the VM status is stopped, but not when the VM is deallocated.

Use the following CLI command to deallocate a VM:

az vm deallocate <resource-group> <vm-name>

In the Azure portal, the Stop button deallocates the VM. However, if you shut down through the OS while logged in, the VM is stopped but not deallocated, so you will still be charged.

Deleting a VM. If you delete a VM, the VHDs are not deleted. That means you can safely delete the VM without losing data. However, you will still be charged for storage. To delete the VHD, delete the file from Blob storage.

To prevent accidental deletion, use a resource lock to lock the entire resource group or lock individual resources, such as the VM.

Security considerations

Use [Azure Security Center][security-center] to get a central view of the security state of your Azure resources. Security Center monitors potential security issues and provides a comprehensive picture of the security health of your deployment. Security Center is configured per Azure subscription. Enable security data collection as described in [Use Security Center]. When data collection is enabled, Security Center automatically scans any VMs created under that subscription.

Patch management. If enabled, Security Center checks whether security and critical updates are missing. Use [Group Policy settings][group-policy] on the VM to enable automatic system updates.

Antimalware. If enabled, Security Center checks whether antimalware software is installed. You can also use Security Center to install antimalware software from inside the Azure portal.

Operations. Use role-based access control (RBAC) to control access to the Azure resources that you deploy. RBAC lets you assign authorization roles to members of your DevOps team. For example, the Reader role can view Azure resources but not create, manage, or delete them. Some roles are specific to particular Azure resource types. For example, the Virtual Machine Contributor role can restart or deallocate a VM, reset the administrator password, create a new VM, and so forth. Other built-in RBAC roles that might be useful for this architecture include DevTest Labs User and Network Contributor. A user can be assigned to multiple roles, and you can create custom roles for even more fine-grained permissions.

Note

RBAC does not limit the actions that a user logged into a VM can perform. Those permissions are determined by the account type on the guest OS.

Use audit logs to see provisioning actions and other VM events.

Data encryption. Consider Azure Disk Encryption if you need to encrypt the OS and data disks.

Deploy the solution

A deployment for this architecture is available on GitHub. It includes a VNet, NSG, a single VM, and an extension described below:

  • VNet. A sample virtual network with a single subnet named web used to host the VM.
  • NSG. A sample NSG with two incoming rules to allow SSH and HTTP traffic to the VM.
  • VM. A sample Linux VM running the latest version of Ubuntu 16.04.3 LTS.
  • Extension. A sample custom script extension used to deploy apache to the Ubuntu VM, and format the two data disks.

Prerequisites

Before you can deploy the reference architecture to your own subscription, you must perform the following steps.

  1. Clone, fork, or download the zip file for the [AzureCAT reference architectures][ref-arch-repo] GitHub repository.

  2. Make sure you have the Azure CLI 2.0 installed on your computer. To install the CLI, follow the instructions in [Install Azure CLI 2.0][azure-cli-2].

  3. Install the Azure building blocks npm package.

  4. From a command prompt, bash prompt, or PowerShell prompt, login to your Azure account by using one of the commands below, and follow the prompts.

    az login
    

    Deploy the solution using azbb

To deploy the sample single VM workload, follow these steps:

  1. Navigate to the virtual-machines\single-vm\parameters\linux folder for the repository you downloaded in the pre-requisites step above.

  2. Open the single-vm-v2.json file and enter a username and SSH key between the quotes, as shown below, then save the file.

    "adminUsername": "",
    "adminsshPublicKey": "",
    
  3. Run azbb to deploy the sample VM as shown below.

    azbb -s <subscription_id> -g <resource_group_name> -l <location> -p single-vm-v2.json --deploy
    

For more information on deploying this sample reference architecture, visit our GitHub repository.

Next steps