Fundamentals of Cloud Security Groups

Cloud security groups (CSGs) are a powerful resource for any organization that operates more than one cloud-based virtual network and wants to assign access to each virtual network independently. To give you some background, security groups are logical containers that you can use to control access to network resources. A typical usage scenario for security groups involves assigning them as sub-groups under an overarching parent group (e.g., “Blue team” might be the parent group, with “Red team” and “Green Team” being child security groups).


The Problem with the Existing Approach


The problem with the existing approach relates to how resource access is controlled. When using security groups, the owner of the parent group is responsible for setting the access rules for child groups. For example, if the blue team is given admin privileges on all resources within the virtual network, all blue team members will have full administrative access. Any changes to the parent group’s access settings will cascade down to all child groups. As a result, it is impossible to have different security settings for each child group and manage the entire network as a single entity. This is inconvenient when you have different departments or business units with different security requirements.


Application of Cloud Security Group


Let’s say you have a multi-tier application deployed on virtual machines. CSGs enable you to assign groups to each tier, then set the group’s access rules to allow or deny access to specific services or resources. This is especially useful for organizations that have multiple virtual networks. For example, you can use CSGs to create a private network for end-user applications, a separate network for network-controlled services (e.g., load balancing, firewall, VPN, etc.), and a public network for guest Internet-facing services. You can also create virtual networks for different departments and assign each department their own CSGs. Each department can then have unique access rights to the virtual network. This is especially useful when you want to restrict the ability of one department to interfere with another.


Why are CSGs Important?


As we’ve discussed, CSGs are a powerful tool that can help you manage network security and access. That being said, they also have some limitations that are important to understand. 



● Access control is based on group members: When specifying access rights for a virtual network, you assign those rights to the security group. In other words, you grant access to the group, not to individual users or devices. 
● CSGs can only be applied to virtual networks 
● Security groups are not retroactive: When you create a new virtual network, you will be able to apply CSGs from the get-go. However, you cannot use CSGs to grant access to existing virtual machines or other network resources. 

Guidelines for Cloud Security Groups


There are some things to keep in mind when creating and managing your CSGs.



● CSGs inherit the parent group’s resources: When creating a new CSG, you have the option of selecting an existing parent group as the parent. If you select an existing parent group, the newly created CSG will include all resources (network interfaces, virtual networks, etc.) associated with the parent group. This allows you to manage a large number of resources with a small number of CSGs.
● CSGs cannot be shared: You can create CSGs to grant access to specific virtual networks. You can also create CSGs to grant access to a specific resource (e.g., network interface, virtual machine, etc.). However, you cannot create CSGs to grant access to more than one virtual network. - CSGs can be applied to VNets and subscriptions: CSGs can be applied to VNets as well as a subscription level. When applied to a subscription level, all VNets within the subscription will inherit the CSG settings. This can be used to manage network security across multiple VNets using a single CSG.

Benefits of CSGs


As we’ve discussed, CSGs are a powerful and flexible tool that can help you manage network security and access. With that said, there are some additional benefits to using CSGs.



● Unified network security: By using CSGs, you can manage network security across multiple VNets with a single set of rules. This means you have one place to configure access rights and one set of rules to maintain.
● Improved network security: Rather than managing network security on a per-VM basis, you can assign access rights to entire VNets at once. This makes it much easier to ensure that the network is properly segmented and that the correct VMs can access the correct resources. 
● Improved network scalability: Using VM-specific security rules is fine when you have a handful of VMs. However, as your network grows, managing access rights on a per-VM basis becomes unwieldy. With CSGs, you can manage network security at the VNet level, making it much easier to scale your network.

Limitations of CSGs


Given all the advantages of using CSGs, you may be wondering why everyone isn’t using them. Well, there are some limitations to keep in mind.



● Some VMs don’t support CSGs: Although most VMs support CSGs, there are a few notable exceptions. 
● Some VMs require a workaround: Some VM types require a workaround when using CSGs. For example, some Linux VM types do not support network interfaces. In this case, you will need to create a rule for each VM to specify the source IP and destination IP. 
● Not retroactive: Unfortunately, you cannot retroactively apply CSGs to existing VMs or networks. This means that you will have to manually assign access rights to each VM and network.

Summary


Cloud security groups are a powerful tool that any organization with multiple virtual networks can benefit from. CSGs can be applied to VNets as well as a subscription level. By doing so, you can manage network security across multiple VNets using a single CSG. Additionally, CSGs allow you to manage network security across multiple VNets with a single set of rules. Also, there are some limitations to keep in mind. With that said, when used correctly, CSGs can help you improve network security and scalability.

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