We’ve been playing with Azure Stack for quite a while now and its pretty easy to forget you’re not using the real Azure. But there are a few key differences that you should always keep in mind when deploying your applications on to Azure Stack; with one of the biggest being around Network Security.
The above diagram is taken from Microsoft Azure’s Best Practices Guide for network security. It shows the various layers of security Azure provides to its customers, both native to the platform itself and configurable by the customer. The current version of Microsoft Azure Stack implements most of these already; Public IPs, Virtual Network Isolation, NSG & UDR and (some) Network Virtual Appliances are already fully implemented within the RTM version of Azure Stack.
At the internet boundary of Azure, Microsoft implements a range of standard network security protections, including the DDoS protection shown in the diagram above but also intelligent services that block known bad actors. These protection services are provided to all Azure customers as Microsoft needs to ensure the availability and stability of their network. Azure Stack however is deployed into your own data centre, which means it sits behind your internet access point. This means you are responsible for providing protection at the internet boundary.
Deploying Azure Stack in your environment can be done in two models, connected and disconnected. In a disconnected model, the tenant workloads within the Azure Stack instance aren’t going to be on the internet. But if your Azure Stack instance is in a connected model, and your Public IP Address range are actual public IPv4 addresses, then this Azure Stack instance looks and feels very much like the real Azure. In this case, treating the security of applications deployed to Azure Stack just like the applications you deploy to the real Azure is vitally important.
Here are some recommendations for workloads deployed to Azure Stack:
- Follow good practice regarding user accounts and passwords; including changing the default passwords, setting strong passwords, and utilise certificates where possible.
- Utilise subnets or virtual networks to segregate internet facing component from protected components.
- Ensure communication to and from the backend, protected or even on-premises network cannot go directly to the internet without going through a firewall or security appliance (more on this below).
- Utilise NSGs to minimise the network surfaces exposed to the internet.
- Don’t have common management ports open to the internet such as RDP or SSH
- If you do need to allow these ports for external management, consider deploying a jump server to reduce the attack surface or using a point-to-site VPN connection to the VNet hosting the resources.
- Consider deploying a NVA such as a next gen firewall. Use UDR’s to ensure egress internet traffic goes via this appliance so you have better control and visibility of what your IaaS VM’s can reach out to, such as SaaS based services like OMS.
- Patch your IaaS VM’s – make sure critical patches are applied ASAP to reduce risk of breach
- For Windows workloads, deploy Anti-malware protection such as Defender. This is available as an extension in Azure Stack is free and easy to deploy, so there’s no excuse not to!
- Harden your IaaS VM’s. Use the best practise available from https://www.cisecurity.org/cis-benchmarks/
Of course, the above guidance trusts that the customers who subscribe to your Azure Stack offers are suitably aware. If you are a CSP operating a multi-tenant Azure Stack platform, although you can control resources to a degree through Plans, Offers and Quotas that customers can consume, you can’t control what they do within their IaaS VM’s. If they deployed a VM with a public IP, has root/administrator enabled and sets a weak password, you can be sure that that will get breached pretty quickly, potentially participating in a botnet and gobbling up your internet bandwidth. This is where you need to have edge security in place, external to the stamp to mitigate these risks.
Consider the following measures:
- Firewall: enforcing firewall rules or access control policies for ingress/egress communication to the external IP address space assigned to Azure Stack.
- IDS or IPS– Intrusion Defence System or Intrusion Prevention System: assessing packets against known issues and attacks and creating alerts or executing real-time responses to attacks and violations.
- Run regular vulnerability scans against the external IP address space assigned to Azure Stack. Identify at the earliest opportunity where a tenant may be exposed to being breached.
- Auditing and Logging: maintain detailed logs for auditing and analysis.
- Reverse Proxy: redirecting incoming requests to the corresponding back-end servers.
- Forward Proxy: Providing NAT and auditing communication initiated from within the network to the internet. Note: The Azure Stack infrastructure only supports a transparent proxy at this stage, but workloads within Azure Stack can utilise a configurable proxy.
Updating the previous diagram and applying it to Azure Stack, you can see where the various security layers could/should be applied:
Finally, there is no ‘one size fits all’ solution to this issue when implementing network security for Azure Stack within your data centre. Factors such as Scale, Price, Certification and Regulation can all factor into a solution but the recommendations above should provide some guidance.