# Capacity reservations for your Application Load Balancer LCU reservations Load balancer Capacity Unit (LCU) reservations allow you to reserve a static minimum capacity for your load balancer. Application Load Balancers automatically scale to support detected workloads and meet capacity needs. When minimum capacity is configured, your load balancer continues scaling up or down based on the traffic received, but also prevents the capacity from going lower than the minimum capacity configured. Consider using LCU reservation in following situations: + You have an upcoming event that will have a sudden, unusual high traffic and want to ensure your load balancer can support the sudden traffic spike during the event. + You have unpredictable spiky traffic due to the nature of your workload for a short period. + You are setting up your load balancer to on-board or migrate your services at a specific start time and need start with a high capacity instead of waiting for auto-scaling to take effect. + You are migrating workloads between load balancers and want to configure the destination to match the scale of the source. **Estimate the capacity that you need** When determining the amount of capacity you should reserve for your load balancer, we recommend performing load testing or reviewing historical workload data that represents the upcoming traffic you expect. Using the Elastic Load Balancing console, you can estimate how much capacity you need to reserve based on the reviewed traffic. Alternatively, you can utilize the CloudWatch metric `PeakLCUs` to determine the level of capacity needed. The `PeakLCUs` metric accounts for peaks in your traffic pattern that the load balancer must scale across all scaling dimensions to support your workload. The `PeakLCUs` metric is different from the `ConsumedLCUs` metric, which only aggregates the billing dimensions of your traffic. Using the `PeakLCUs` metric is recommended to ensure your LCU reservation is adequate during load balancer scaling. When estimating capacity, use a per-minute `Sum` of `PeakLCUs`. If you don't have historical workload data to reference and cannot perform load testing, you can estimate capacity needed using the LCU reservation calculator. The LCU reservation calculator uses data based on historical workloads AWS observe and may not represent your specific workload. For more information, see [Load Balancer Capacity Unit Reservation Calculator](https://exampleloadbalancer.com/ondemand_capacity_reservation_calculator.html). **Minimum and maximum values for an LCU reservation** The total reservation request must be at least 100 LCU. The maximum value is determined by the quotas for your account. For more information, see [Load Balancer Capacity Units](load-balancer-limits.md#lcu-quotas). # Request Load balancer Capacity Unit reservation for your Application Load Balancer Request reservation Before you use LCU reservation, review the following: + Capacity is reserved at the regional level and is evenly distributed across availability zones. Confirm you have enough evenly distributed targets in each availability zone before turning on LCU reservation. + LCU reservation requests are fulfilled on a first come first serve basis, and depends on available capacity for a zone at that time. Most requests are typically fulfilled within a few minutes, but can take up to a few hours. + To update an existing reservation, the previous request must be provisioned or failed. You can increase reserved capacity as many times as you need, however you can only decrease the reserved capacity two times per day. + You will continue to incur charges for any reserved or provisioned capacity until they are terminated or cancelled. ------ #### [ Console ] **To request an LCU reservation** 1. Open the Amazon EC2 console at [https://console.aws.amazon.com/ec2/](https://console.aws.amazon.com/ec2/). 1. On the navigation pane, choose **Load Balancers**. 1. Select the load balancer name. 1. On the **Capacity** tab, choose **Edit LCU Reservation**. 1. Select **Historic reference based estimate**. 1. Select the reference period to view the recommended reserved LCU level. 1. If you do not have historic reference workload, you can choose **Manual estimate** and enter the number of LCUs to be reserved. 1. Choose **Save**. ------ #### [ AWS CLI ] **To request an LCU reservation** Use the [modify-capacity-reservation](https://docs.aws.amazon.com/cli/latest/reference/elbv2/modify-capacity-reservation.html) command. ``` aws elbv2 modify-capacity-reservation \ --load-balancer-arn load-balancer-arn \ --minimum-load-balancer-capacity CapacityUnits=100 ``` ------ #### [ CloudFormation ] **To request an LCU reservation** Update the [AWS::ElasticLoadBalancingV2::LoadBalancer](https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/aws-resource-elasticloadbalancingv2-loadbalancer.html) resource. ``` Resources: myLoadBalancer: Type: 'AWS::ElasticLoadBalancingV2::LoadBalancer' Properties: Name: my-alb Type: application Scheme: internal Subnets: - !Ref subnet-AZ1 - !Ref subnet-AZ2 SecurityGroups: - !Ref mySecurityGroup MinimumLoadBalancerCapacity: CapacityUnits: 100 ``` ------ # Update or cancel Load Balancer Capacity Unit reservations for your Application Load Balancer Update or cancel reservation If the traffic patterns for your load balancer change, you can update or cancel the LCU reservation for your load balancer. The status of the LCU reservation must be **Provisioned**. ------ #### [ Console ] **To update or cancel an LCU reservation** 1. Open the Amazon EC2 console at [https://console.aws.amazon.com/ec2/](https://console.aws.amazon.com/ec2/). 1. On the navigation pane, choose **Load Balancers**. 1. Select the load balancer name. 1. On the **Capacity** tab, do one of the following: 1. To update the LCU reservation choose **Edit LCU Reservation**. 1. To cancel the LCU reservation, choose **Cancel Capacity**. ------ #### [ AWS CLI ] **To cancel an LCU reservation** Use the [modify-capacity-reservation](https://docs.aws.amazon.com/cli/latest/reference/elbv2/modify-capacity-reservation.html) command. ``` aws elbv2 modify-capacity-reservation \ --load-balancer-arn load-balancer-arn \ --reset-capacity-reservation ``` ------ # Monitor Load Balancer Capacity Unit reservation for your Application Load Balancer Monitor reservation **Reservation status** The following are the possible status values for an LCU reservation: + `pending` ‐ Indicates the reservation it is in the process of provisioning. + `provisioned` ‐ Indicates the reserved capacity is ready and available to use. + `failed` ‐ Indicates the request cannot be completed at the time. + `rebalancing` ‐ Indicates an availability zone has been added or removed and the load balancer is rebalancing capacity. **LCU utilization** The `ReservedLCUs` metric is reported on a per-minute basis. Capacity is reserved on an hourly basis. For example, if you have a LCU reservation of 6,000, the one-hour total for `ReservedLCUs` is 6,000, and the one-minute total is 100. To determine your reserved LCU utilization, refer to the `PeakLCUs` metric. You can set CloudWatch alarms to compare the per-minute `Sum` of `PeakLCUs` against your reserved capacity value, or the per-hour `Sum` of `ReservedLCUs`, to determine whether you have reserved enough capacity to meet your needs. ------ #### [ Console ] **To view the status of an LCU reservation** 1. Open the Amazon EC2 console at [https://console.aws.amazon.com/ec2/](https://console.aws.amazon.com/ec2/). 1. On the navigation pane, choose **Load Balancers**. 1. Select the load balancer name. 1. On the **Capacity** tab, you can view the **Reservation Status** and **Reserved LCU** value. ------ #### [ AWS CLI ] **To monitor the status of an LCU reservation** Use the [describe-capacity-reservation](https://docs.aws.amazon.com/cli/latest/reference/elbv2/describe-capacity-reservation.html) command. ``` aws elbv2 describe-capacity-reservation \ --load-balancer-arn load-balancer-arn ``` ------