Last Updated: Dec 05, 2017

Alibaba Cloud Server Load Balancer is a load balancing service that distributes traffic among multiple backend ECS instances. It extends the service capability of an application system by distributing traffic and enhances availability by eliminating single point of failures (SPOFs).

Service Level Indicators

Service Functions

Server Load Balancer provides advanced functions such as self-management, automatic fault recovery, and network attack prevention. It is applicable to community websites, enterprise websites, portals, e-commerce websites, SAAS applications, and game applications. For details about all functions of Server Load Balancer, refer to the instructions, technical documents and help documents on the official website of Alibaba Cloud. All functional changes that may affect users will be announced to users.

Service Availability

Service availability: not lower than 99.95% for a single instance.

Service availability calculation formula: Actual instance availability = (Total time – Actual unavailable time)/Total time × 100%

Actual unavailable time = Unavailable time × Percentage of the user’s reduced service traffic, applicable to Layer-4 VIP and Layer-7 VIP.


(1) Server Load Balancer balances the loads of instances in cluster mode. When a server in the system cluster is faulty, its services are taken over by other servers. Only a portion of the user’s service traffic is affected. Therefore, the actual unavailable time must be calculated based on the percentage of the traffic on the faulty servers to the total traffic of the cluster.

(2) The actual instance availability is calculated by month.

Fault measurement point:

Measurement point Whether to include in availability calculation
Instance running status Networking User’s network No
ISP network No
Basic network IDC (fault due to force majure is not included in service unavailability calculation) Yes
Intranet interconnection ACL Yes
Security Network attack (an attack against a single user is not counted, whereas an attack against Alibaba Cloud is counted) Yes
Product Service unavailable
The following faults are not included in unavailability calculation: faults caused by the user’s application server configuration (for example, heath check failure due to the user’s firewall rule restrictions and incorrect health check configuration), faults caused by the service capability bottleneck of backend servers, and faults of backend servers.
Faults of servers, storage devices, and other hardware Yes
Faults of the Alibaba Cloud system software Yes
Service unavailable due to system changes Yes
Management Console Creating an Instance No
Configuration management (for example, health check and session persistence) No
Presentation exception (for example, health check results) No
API Creating an Instance No
Configuration management (for example, health check and session persistence) No
Presentation exception (for example, health check results) No

Service Resource Allocation Capability

The Server Load Balancer system supports flexible and automatic resizing based on the cluster service capability. You can upgrade public bandwidth online in real time or increase the loan peak’s upper limit for the Pay-As-You-Go instance based on your service need.

Fault Recovery Capability

Alibaba Cloud provides 24/7 operation and maintenance support for paying users’ Server Load Balancer instances through fault reporting through online tickets or by phone. A complete set of fault emergency response mechanisms is provided, including fault monitoring, automatic alarm generation, fast locating, and fast recovery.

Network Access Performance

When you activate Alibaba Cloud Server Load Balancer, you can select the public egress bandwidth for each Server Load Balancer instance or select the Pay-As-You-Go method. The configuration range of the public egress bandwidth is 1–1,000 Mbps.Alibaba Cloud uses BGP multi-line access to ensure network access quality for users.

Service Measurement Accuracy

Server Load Balancer uses an accurate and transparent measuring and billing system. Alibaba Cloud performs billing based on your actual usage of Server Load Balancer instances and deducts payments in real time. For specific billing standards, refer to the effective billing modes and prices released on the official website of Alibaba Cloud. The original billing logs of users are retained for at least 3 years by default for future reference.

Terms and Conditions of Service Compensation

Alibaba Cloud Server Load Balancer supports 100 times of compensation guaranteed for faults.

Scope of Compensation

If a Server Load Balancer instance cannot be used normally due to a fault caused by Alibaba Cloud, Alibaba Cloud will compensate for the fault time. However, faults due to the following causes are not covered by compensation:

(1) System maintenance activities by Alibaba Cloud on prior notice, including cutovers, repairs, upgrades and fault simulation drills;

(2) Any faults or configuration changes on the networks or equipment which do not belong to Alibaba Cloud;

(3) User’s applications or data being hacked;

(4) Loss or leakage of data, passwords, codes, etc. due to the user’s improper maintenance or confidentiality;

(5) Users’ negligence or authorized operations;

(6) Failure to use Server Load Balancer normally due to an ECS fault;

(7) Force majeure or unforeseen events;

(8) Failure to use Server Load Balancer normally due to causes not related to Alibaba Cloud.

Proposed Compensation

(1) Fault time = Resolution time of the fault – Start time of the fault.

(2) Faults of Server Load Balancer are compensated by coupons instead of cash.

(3) Compensation payment for a single device = Average hourly cost during the 24 hours before the occurrence of the fault/60 × Fault time × 100. (The total compensation payment shall not exceed the total payment that has been made for Server Load Balancer.)


(1) If the user has not been using the service for at least 24 hours, the compensation will be calculated based on the average rate for the actual usage time.

(2) The fault time is calculated by minutes.

(3) The compensation only covers Server Load Balancer, but does not cover the ECS instances attached to Server Load Balancer instances.


Alibaba Cloud is entitled to adjust certain service quota in this SLA according to actual changes, and release announcements on the Alibaba Cloud official website or send emails or written notices as soon as possible to notify users of the adjustments.

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