Burstable instances are an economical instance type that is intended to meet burst performance requirements in entry-level computing scenarios. This topic describes the features, use scenarios, instance families and instance types, baseline performance, CPU credits, and performance modes of burstable instances.

What are burstable instances?

Burstable instances use CPU credits to maintain computing performance and are suitable for scenarios where CPU utilization is typically low but experiences occasional bursts. Burstable instances can accumulate CPU credits and consume the credits to burst performance above their CPU baseline as needed by your workloads. This consumption pattern does not affect the environments or applications that are deployed on the instances. Burstable instances are more flexible and cost-effective than other types of instances in terms of CPU utilization.

The CPU credit mechanism allows you to save computing power during off-peak hours for use during peak hours and reduce costs. If you have unplanned performance requirements, you can enable unlimited mode for your burstable instances.

The following burstable instance families are available:
Note Burstable instances are special shared instances. For more information about other shared instance families, see Shared instance families.
The following table describes the baseline performance, CPU credits, and performance modes of burstable instances.
Term Description References
baseline performance The amount of vCPU capacity that is continuously provisioned to a burstable instance. Baseline performance varies based on instance types. Baseline performance
initial CPU credit A limited number of CPU credits that are allocated to a new burstable instance. 30 initial credits are allocated to each vCPU. These credits cannot be replenished after they are depleted. CPU credits
CPU credit balance The net credits that are accrued when the earned CPU credits exceed the consumed credits. You can consume these credits to run instances above their baseline performance levels. CPU credits
Max CPU credit balance The maximum number of CPU credits that can be earned by a burstable instance within a 24-hour period. The CPU credit balance is valid for 24 hours. Each burstable instance earns CPU credits at a set rate that is determined by the instance type, and can accrue only a limited number of credits in its CPU credit balance. CPU credits
performance mode
A burstable instance can run in standard or unlimited mode.
  • A burstable instance in standard mode runs below its baseline performance if its CPU credits are depleted.
  • A burstable instance in unlimited mode allows you to overdraw or pay for additional CPU credits to sustain the CPU utilization above its baseline performance level at anytime. You may be charged for using these CPU credits.
Performance modes
advance CPU credit The CPU credits that a burstable instance will earn over the next 24-hour period. You may be charged for using these CPU credits. Advance CPU credits can be used only when unlimited mode is enabled. Performance modes
overdrawn CPU credit The CPU credits that a burstable instance consumes after it depletes its advance credits to keep running above its baseline performance level. You are charged for using overdrawn CPU credits. Overdrawn CPU credits can be used only when unlimited mode is enabled. Performance modes

Use scenarios

When you purchase an enterprise-level instance, its vCPUs are exclusively reserved for your use. You are charged for the vCPUs regardless of whether you fully utilize their performance. If you require a high level of CPU performance for only a portion of a day, some vCPU resources are left idle for the remainder of the entire day but you are still charged for these unused resources. To prevent this situation, you can use burstable instances to better meet your business requirements.

Burstable instances apply to scenarios that require higher-than-normal performance for a specific period, such as stress testing service applications, lightweight applications, microservices, and web application servers. We recommend that you evaluate your business requirements to determine the performance levels required during off-peak and peak hours before you make a purchase. The baseline performance of the instances that you purchase must meet your business requirements during off-peak hours to achieve the required performance at significantly lower costs.
Note If the purchased burstable instances do not meet your requirements, you can change the configurations. For more information, see Configuration changes.

Baseline performance

Baseline performance is the amount of vCPU capacity that is continuously provisioned to a burstable instance. Baseline performance varies based on instance types. You can view the baseline performance of different instance types from the Baseline CPU computing performance column of the instance type tables.

CPU credits

CPU credits can be described as computing resources that are available for your use. These computing resources determine the computing performance that your burstable instances can deliver. The following section describes the terms and examples related to CPU credits:

  • Initial CPU credits

    When you create a burstable instance, 30 CPU credits are allocated to each vCPU of the instance, which are initial CPU credits. These credits enable you to complete deployment tasks when you start the instance.

    For example, an ecs.t5-lc1m2.large instance has two vCPUs and earns 60 initial CPU credits when it is created. An ecs.t5-c1m1.xlarge instance has four vCPUs and earns 120 initial CPU credits when it is created.

  • Rate of earning CPU credits

    When a burstable instance starts, it begins to consume CPU credits to maintain its computing performance. At the same time, the instance also earns CPU credits at a set rate that is determined by the instance type. The number of CPU credits that a vCPU can earn per hour varies based on instance types. The CPU credits per hour column in the instance type tables indicates the CPU credits that all the vCPUs of an instance can earn per hour.

    For example, 25% baseline performance of an ecs.t5-c1m1.large instance indicates that the CPU credits that a vCPU of the instance earns per hour can keep the vCPU running at 25% utilization for 1 hour or at 100% utilization for 15 minutes (60 × 25%). In response to its baseline performance, each vCPU earns 15 CPU credits per hour. An ecs.t5-c1m1.large instance has two vCPUs and earns 30 CPU credits per hour.

  • CPU credit balance

    If the earned CPU credits exceed the consumed credits, the net credits are accrued as CPU credit balance. The CPU credit balance is valid for 24 hours. Each burstable instance earns CPU credits at a set rate that is determined by the instance type, and can accrue only a limited number of credits in its CPU credit balance. The maximum CPU credit balance of a specific instance type is the maximum number of CPU credits that the instance can earn within a 24-hour period. For more information, see the Max CPU credit balance column in the instance type tables.

    For example, an ecs.t5-c1m1.large instance can earn 30 CPU credits per hour. The maximum CPU credit balance that the instance can earn is 720 (30 × 24) credits.

  • Rate of consuming CPU credits
    The rate at which a burstable instance consumes CPU credits is determined based on the number of vCPUs, CPU utilization, and operating hours of the instance. For example, one CPU credit is consumed in the following scenarios:
    • One vCPU runs at 100% utilization for 1 minute.
    • One vCPU runs at 50% utilization for 2 minutes.
    • Two vCPUs run at 25% utilization for 2 minutes.
    When a burstable instance starts, it begins to consume CPU credits to maintain its computing performance. Initial credits that cannot be replenished are consumed first. When the initial credits are depleted, the instance continues to consume the accrued CPU credits.
    • When the CPU utilization is below the baseline, the credits earned are greater than the credits consumed and the CPU credit balance increases.
    • When the CPU utilization is equal to the baseline, the credits earned are equal to the credits consumed and the CPU credit balance remains unchanged.
    • When the CPU utilization is higher than the baseline, the credits earned are less than the credits consumed and the CPU credit balance decreases.
In different scenarios, stopping your instances may have different impacts on your CPU credits:
  • If a pay-as-you-go instance is stopped in standard mode, the CPU credit balance of the instance is retained and the instance continues to earn CPU credits.
  • If a pay-as-you-go instance is stopped in economical mode, the CPU credit balance of the instance becomes invalid and the instance cannot continue to earn credits. When the instance is started again, it receives initial credits and begins to earn credits again.
  • If a pay-as-you-go instance is stopped due to an overdue payment, the CPU credit balance of the instance is retained but the instance cannot continue to earn credits until you complete the payment.
  • If a subscription instance expires and is stopped, the CPU credit balance of the instance is retained but the instance cannot continue to earn credits. When the instance is reactivated, it begins to earn credits again.

Performance modes

A burstable instance can run in standard or unlimited mode.
  • Standard mode

    The performance of a burstable instance in standard mode is limited by the availability of CPU credits. After the instance depletes all of its initial credits and CPU credit balance, the instance cannot run above its baseline performance level. When the CPU credit balance is low, the instance gradually reduces performance to its baseline level within 15 minutes. This way, the instance does not experience a sharp performance drop-off when its CPU credit balance is depleted.

    Standard mode is applicable to scenarios such as lightweight web servers, development and testing environments, and databases that have low and medium performance. In these scenarios, workloads are stable, instances do not run above the baseline performance level for an extended period of time, and bursts in performance are only occasionally required.

  • Unlimited mode
    The performance of a burstable instance in unlimited mode is not limited by the availability of CPU credits. You can overdraw or pay for additional CPU credits to obtain performance boosts at anytime. If your instances continue to run above the baseline performance level after the initial CPU credits and accrued credits are depleted, the instance begins to consume advance CPU credits and overdrawn CPU credits.
    • Advance CPU credits: Advance CPU credits are the credits that a burstable instance will earn over the next 24-hour period. You may be charged for using these CPU credits.
    • Overdrawn CPU credits: Overdrawn CPU credits are the CPU credits that a burstable instance consumes after it depletes its advance credits to keep running above its baseline performance level. You are charged for using overdrawn credits.
    Note For more information about the fees and billing rules of using advance and overdrawn CPU credits, see Impact of performance modes on billing (additional fees).
    The following figure shows how the CPU credits change when an instance is running in unlimited mode. Advance and overdrawn CPU credits
    Note If the instance has consumed advance CPU credits and is stopped in economical mode, is released, has its configurations changed, or switches to standard mode before the advance CPU credits are replenished, you are charge a lump sum amount for the consumed advance CPU credits.
    You can enable unlimited mode for your burstable instances if you want to consume advance or overdrawn CPU credits in addition to your credit balance to meet burst performance requirements. Examples:
    • Some events such as new feature releases, e-commerce promotions, and website promotions cause a substantial increase in your workloads. High CPU performance is required during this period of time. In this case, you can enable unlimited mode for your burstable instances. You can disable this mode to save costs when the workload peak ends.
    • Some web applications may require CPU bursts for a specific period during a day, but the daily average CPU utilization is below the baseline. In this case, you can enable unlimited mode for your instances during peak hours to ensure a positive user experience. If the CPU credits that you have earned during off-peak hours can offset the advance CPU credits that you consumed during peak hours, you can continue to provide a positive user experience at no additional costs.

By default, standard mode is enabled when you create a burstable instance. For more information about how to enable unlimited mode, see Enable the unlimited mode.

For more information about how CPU credits change when an instance is running in different performance modes, see CPU credit change examples.

Configuration changes

When you monitor a burstable instance, you may find that its CPU utilization remains above or below the baseline for an extended period of time. This indicates that the instance type is not suitable for your business. We recommend that you re-evaluate the instance type to decide whether to select another burstable or enterprise-level instance type. The operation of changing instance types varies based on the billing methods. For more information, see Overview of instance upgrade and downgrade.

t6, burstable instance family

Features:
  • Provides baseline CPU performance and is burstable but limited by accrued CPU credits.
  • Is more cost-effective when compared with the t5 burstable instance family.
  • Compute:
    • Uses 2.5 GHz Intel® Xeon® Cascade Lake processors that deliver a turbo frequency of 3.2 GHz.
    • Uses DDR4 memory.
  • Storage:
    • Supports enhanced SSDs (ESSDs), standard SSDs, and ultra disks.
      Note ESSDs at performance level (PL) 2 and 3 cannot provide maximum performance due to the specification limits of burstable instances. We recommend that you use enterprise-level instances or ESSDs that are at lower performance levels.
  • Network:
    • Supports IPv6.
    • Supports only virtual private clouds (VPCs).
    • Delivers a bandwidth up to 4 Gbit/s.
  • Applicable scenarios:
    • Web application servers
    • Lightweight applications and microservices
    • Development and testing environments
Instance types
Instance type vCPUs Memory (GiB) Baseline CPU performance CPU credits per hour Max CPU credit balance Base bandwidth (Gbit/s) Packet forwarding rate (pps) NIC queues ENIs Private IP addresses per ENI
ecs.t6-c4m1.large 2 0.5 5% 6 144 0.08 40,000 1 2 2
ecs.t6-c2m1.large 2 1.0 10% 12 288 0.08 60,000 1 2 2
ecs.t6-c1m1.large 2 2.0 20% 24 576 0.08 100,000 1 2 2
ecs.t6-c1m2.large 2 4.0 20% 24 576 0.08 100,000 1 2 2
ecs.t6-c1m4.large 2 8.0 30% 36 864 0.08 100,000 1 2 2
ecs.t6-c1m4.xlarge 4 16.0 40% 96 2,304 0.16 200,000 1 2 6
ecs.t6-c1m4.2xlarge 8 32.0 40% 192 4,608 0.32 400,000 1 2 6
Note
  • Secondary elastic network interfaces (ENIs) cannot be bound to instances of this instance family while the instances are being created and can be bound after the instances are created. When you bind secondary ENIs to or unbind them from instances of the following instance types, the instances must be in the Stopped state: ecs.t6-c1m1.large, ecs.t6-c1m2.large, ecs.t6-c1m4.large, ecs.t6-c2m1.large, and ecs.t6-c4m1.large.
  • You can go to the ECS Instance Types Available for Each Region page to view the instance types available in each region.
  • For more information about these specifications, see Instance type specifications.

t5, burstable instance family

Features:
  • Provides baseline CPU performance and is burstable but limited by accrued CPU credits.
  • Offers a balance between compute, memory, and network resources.
  • Compute:
    • Offers multiple CPU-to-memory ratios.
    • Uses 2.5 GHz Intel® Xeon® processors.
    • Uses DDR4 memory.
  • Network:
    • Supports IPv6.
    • Supports only VPCs.
  • Applicable scenarios:
    • Web application servers
    • Lightweight applications and microservices
    • Development and testing environments
Instance types
Instance type vCPUs Memory (GiB) Baseline CPU performance CPU credits per hour Max CPU credit balance Bandwidth (Gbit/s) Packet forwarding rate (pps) NIC queues ENIs Private IP addresses per ENI
ecs.t5-lc2m1.nano 1 0.5 20% 12 288 0.1 40,000 1 2 2
ecs.t5-lc1m1.small 1 1.0 20% 12 288 0.2 60,000 1 2 2
ecs.t5-lc1m2.small 1 2.0 20% 12 288 0.2 60,000 1 2 2
ecs.t5-lc1m2.large 2 4.0 20% 24 576 0.4 100,000 1 2 2
ecs.t5-lc1m4.large 2 8.0 20% 24 576 0.4 100,000 1 2 2
ecs.t5-c1m1.large 2 2.0 25% 300,000 720 0.5 100,000 1 2 2
ecs.t5-c1m2.large 2 4.0 25% 300,000 720 0.5 100,000 1 2 2
ecs.t5-c1m4.large 2 8.0 25% 300,000 720 0.5 100,000 1 2 2
ecs.t5-c1m1.xlarge 4 4.0 25% 60 1,440 0.8 200,000 1 2 6
ecs.t5-c1m2.xlarge 4 8.0 25% 60 1,440 0.8 200,000 1 2 6
ecs.t5-c1m4.xlarge 4 16.0 25% 60 1,440 0.8 200,000 1 2 6
ecs.t5-c1m1.2xlarge 8 8.0 25% 120 2,880 1.2 400,000 1 2 6
ecs.t5-c1m2.2xlarge 8 16.0 25% 120 2,880 1.2 400,000 1 2 6
ecs.t5-c1m4.2xlarge 8 32.0 25% 120 2,880 1.2 400,000 1 2 6
ecs.t5-c1m1.4xlarge 16 16.0 25% 240 5,760 1.2 600,000 1 2 6
ecs.t5-c1m2.4xlarge 16 32.0 25% 240 5,760 1.2 600,000 1 2 6
Note
  • Secondary ENIs cannot be bound to instances of this instance family while the instances are being created and can be bound after the instances are created. When you bind secondary ENIs to or unbind them from instances of the following instance types, the instances must be in the Stopped state: ecs.t5-lc2m1.nano, ecs.t5-c1m1.large, ecs.t5-c1m2.large, ecs.t5-c1m4.large, ecs.t5-lc1m1.small, ecs.t5-lc1m2.large, ecs.t5-lc1m2.small, and ecs.t5-lc1m4.large.
  • You can go to the ECS Instance Types Available for Each Region page to view the instance types available in each region.
  • For more information about these specifications, see Instance type specifications.