A spot instance provides a billing mode of CVM. It features a discounted price and a system interruption mechanism, which means that you can purchase a spot instance at a discounted price, but the system may automatically repossess it. When you use a spot instance, the operations are almost the same as what you do with a pay-as-you-go CVM instance, including console operations, remote login, service deployment, and association with a VPC.
System interruption due to insufficient supply: Currently, spot instances will not be interrupted due to the price reason, but may be interrupted if spot instances are in short supply. If the supply is insufficient, Tencent Cloud will randomly repossess allocated spot instances without retaining the instance data.
Available in almost all regions: Spot instances are available in almost all Tencent Cloud regions. The instance types supported by spot instances are the same as those supported by pay-as-you-go instances. For the latest regions and instance types supported, see Spot Instances.
Features
1. Cost-effectiveness
Spot instances are sold at a discount of up to 95% off the prices of pay-as-you-go instances.
Discount range: Spot instances are sold at a discount of up to 95% off the price of pay-as-you-go instances of the same specification.
Exclusions: The discount only applies to CVM CPU and memory. Other items including system disks, data disks, bandwidth, and paid images are not eligible for the discount.
Price fluctuations: The discount is stable for a period of time. However, if there are bulk purchases in an availability zone, the price may fluctuate.
2. System interruption mechanism
Unlike pay-as-you-go instances which can only be released by users, spot instances may be interrupted by the system due to price or resource availability reasons.
System interruption due to insufficient supply: Currently, spot instances will not be interrupted due to the price reason, but may be interrupted if spot instances are in short supply. If the supply is insufficient, Tencent Cloud will randomly repossess allocated spot instances without retaining the instance data.
Non-applicable Scenarios
As spot instances may be interrupted, their lifecycle is not under your control. Therefore, it is not recommended to run services with high stability requirement on a spot instance. For example:
Database services
Online and website services without load balancers
Core control nodes in a distributed architecture
Prolonged big data computing job lasting over 10 hours
Applicable Scenarios and Industries
Applicable scenarios
Big data computing
Online and website services with load balancers
Web crawler service
Other computing scenarios with fine granularity or support for checkpoint restart
Applicable industries
Gene sequencing and analysis
Drug crystal form analysis
Video transcoding and rendering
Financial and transaction data analysis
Image and multimedia processing
Science calculations, such as in geography and hydromechanics.
Limits and Restrictions
Quota limits: Currently, the spot instances for each account per availability zone can contain up to 50 vCPU cores in total. To increase the quota, please submit a ticket.
Purchase limits: Vouchers are not available to spot instances.
Operation restriction 1: You cannot upgrade and degrade the configuration of spot instances.
Operation restriction 3: No charges when shut down is not supported for spot instances.
Operation restriction 4: System reinstallation is not supported for spot instances.
Operation restriction 5: You cannot expand the system disks and data disks of spot instances.
Best Practices
1. Splitting tasks
Split a prolonged task into fine-grained subtasks for lower possibility of interruption.
Use a big data suite such as EMR that comes with a splitting mechanism.
2. Using load balancers to ensure the stability of online and website services
Use load balancers, such as CLB, at the access layer.
Use a combination of some pay-as-you-go instances and many spot instances for backend resources.
Monitor the interruptions of spot instances and remove instances that are about to be interrupted from the CLB.
3. Using a computing scheduling mode that supports checkpoint restart
Store intermediate computing results on permanent storage products such as COS, CFS, and NAS.
Be aware of the instance metadata to monitor which instances are about to be interrupted and save the computing results within the retention period of 2 minutes.
Resume the last computing when a spot instance is started again.
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