10 VMware Affinity Rules Best Practices
There are a few best practices to keep in mind when using VMware affinity rules. Here are 10 of them.
VMware affinity rules are used to control the placement of virtual machines on physical hosts. These rules can be used to ensure that virtual machines are placed on the most appropriate host, or to ensure that virtual machines are not placed on the same host.
In this article, we will discuss 10 best practices for using VMware affinity rules. We will discuss how to use affinity rules to improve performance, reduce costs, and ensure high availability. We will also discuss how to use affinity rules to ensure that virtual machines are placed on the most appropriate host.
1. Use affinity rules to keep VMs together on the same host
Keeping VMs together on the same host helps to reduce latency and improve performance. This is because when a VM is running on one host, it can access resources from that host more quickly than if it were spread across multiple hosts.
Additionally, keeping VMs together on the same host also reduces complexity in your environment. By having fewer VMs spread across fewer hosts, you have less to manage and monitor. Finally, using affinity rules can help you save money by reducing the number of physical servers needed to run your virtual machines.
2. Use anti-affinity rules to ensure that VMs are kept apart on different hosts
Anti-affinity rules ensure that VMs are kept apart on different hosts, which helps to prevent resource contention and improve performance. This is especially important for mission-critical applications or services that require high availability. By keeping the VMs separate, you can reduce the risk of a single host failure taking down multiple VMs at once.
Additionally, anti-affinity rules help to keep your environment secure by preventing malicious actors from targeting multiple VMs with a single attack. By spreading out the VMs across multiple hosts, it becomes much more difficult for attackers to gain access to all of them at once.
3. Do not use both affinity and anti-affinity rules at the same time for a VM or group of VMs
Affinity rules are used to keep VMs together on the same host, while anti-affinity rules are used to keep them apart. If both types of rules are applied at the same time, it can cause conflicts and lead to unexpected behavior. For example, if a VM is configured with an affinity rule that says it should stay on the same host as another VM, but also has an anti-affinity rule that says it should not be on the same host as another VM, then the two rules will conflict and the VM may end up being moved around unexpectedly.
To avoid this issue, make sure you only use one type of rule (either affinity or anti-affinity) for any given VM or group of VMs.
4. Be careful when using DRS with affinity and anti-affinity rules, as it may break them
DRS is a powerful tool that can help optimize resource utilization, but it should be used with caution when affinity and anti-affinity rules are in place.
When DRS is enabled, it will attempt to move virtual machines around the cluster to balance resources. This could potentially break any existing affinity or anti-affinity rules if the VMs are moved to different hosts. To prevent this from happening, you should set up your DRS settings so that they don’t conflict with any of your affinity/anti-affinity rules. You can also use DRS groups to ensure that certain VMs stay together on the same host.
5. Affinity and anti-affinity rules can be used in conjunction with vSphere HA admission control
When you set up affinity and anti-affinity rules, they help ensure that the virtual machines (VMs) are placed on different hosts. This helps to prevent a single host from becoming overloaded with VMs if one of them fails or needs to be restarted. By using these rules in conjunction with vSphere HA admission control, you can also make sure that there is enough capacity available for all of your VMs in case of an unexpected failure. This ensures that your applications remain highly available and performant even during times of high demand.
6. When creating an affinity rule for a VM, you must select either “Must run on hosts in group” or “Should run on hosts in group”
When you select “Must run on hosts in group”, the VM will always be placed on one of the specified hosts. This is useful when you need to ensure that a particular VM runs on specific hardware, or if you want to guarantee that certain VMs are running together for performance reasons.
On the other hand, selecting “Should run on hosts in group” allows the VM to be placed on any host, but it will prefer the ones specified in the rule. This is useful when you want to make sure that a VM is not placed on certain hosts, such as those with limited resources.
7. When creating an anti-affinity rule for a VM, you must select either “Must not run on hosts in group” or “Should not run on hosts in group”
The “Must not run on hosts in group” option ensures that the VM will never be placed on a host within the specified group. This is useful for applications or services that must remain separate from each other, such as databases and web servers.
The “Should not run on hosts in group” option allows the VM to be placed on a host within the specified group if there are no other suitable options available. This is useful when you want to ensure that VMs are spread out across multiple hosts but still allow them to be placed together if necessary.
8. You cannot create an affinity rule for a cluster if there is only one ESXi host in the cluster
Affinity rules are used to control the placement of virtual machines on ESXi hosts in a cluster. When you create an affinity rule, it will be applied to all ESXi hosts in the cluster. If there is only one host in the cluster, then the rule cannot be applied because there is no other host for the VMs to be placed on.
Therefore, if you want to use affinity rules, make sure that your clusters have at least two ESXi hosts. This way, when you create an affinity rule, it can be applied to both hosts and ensure that the VMs are placed according to the rule.
9. You cannot create an anti-affinity rule for a cluster if there is only one ESXi host in the cluster
An anti-affinity rule is used to ensure that virtual machines are not placed on the same ESXi host. This helps prevent resource contention and ensures high availability in case of a hardware failure. However, if there is only one ESXi host in the cluster, then it would be impossible to create an anti-affinity rule since there is no other host for the VMs to be placed on. Therefore, it’s important to make sure that your clusters have at least two ESXi hosts before attempting to create an anti-affinity rule.
10. If you have two clusters, each with three ESXi hosts, you can create a single affinity rule for
By creating a single affinity rule, you can ensure that the workloads are evenly distributed across all six hosts. This will help to maximize resource utilization and minimize contention for resources between clusters. Additionally, it will also reduce the risk of overloading any one host or cluster with too many virtual machines. Finally, this approach allows for more flexibility in terms of scaling up or down as needed.