Tencent Cloud Cloud Load Balancer (CLB) is a secure and fast traffic distribution service. Inbound traffic can be automatically distributed to multiple Cloud Virtual Machine (CVM) instances in the cloud via CLB, improving service capabilities systematically and eliminating single points of failure. CLB supports hundreds of millions of connections and tens of millions of concurrent requests, making it easy to handle high-traffic access and meet demanding business needs.
One single CLB cluster (not one instance) supports up to 120 million concurrent connections and can handle up to 40 Gbps of traffic bandwidth or process 6 million data packets per second. This enables you to easily sustain ecommerce websites, social networking platforms and gaming businesses with over 10 million daily page views.
One CLB cluster consists of 4 physical servers, offering an availability of up to 99.95%. In the extreme case where only one CLB instance is available, it can still support over 30 million concurrent connections. The cluster system will remove faulty instances in time and keep the healthy ones to ensure that the backend server continues to operate properly.
The CLB cluster scales the service capabilities of the application system elastically according to the business load, and automatically creates and releases CVM instances through the dynamic scaling group of Auto Scaling. These features, in conjunction with a dynamic monitoring system and a billing system that is accurate to the second, eliminate your need to manually intervene or estimate resource requirements, helping you reasonably allocate computing resources and prevent resource waste.
With the aid of BGP Anti-DDoS system, CLB is capable of defending against most network attacks (such as DDoS, CC and web intrusion attacks) and cleansing attacking traffic in a matter of seconds, which greatly avoids the occurrence of blocked IPs and full occupancy of bandwidth. CLB's built-in synproxy anti-attack mechanism prevents backend CVMs from being attacked and overloaded before BGP system takes effect, ensuring the data security and stability.
CLB eliminates your need to invest in additional load balancing hardware and time devoted to tedious OPS work, saving you up to 99% of hardware and labor costs. CLB is billed on a pay-as-you-go basis. You only pay for what you use, and you can create and terminate CLB instances at any time according to the business needs.
CLB supports requests from layer 4 protocols (including TCP and UDP) and layer 7 protocols (including HTTP and HTTPS). Its centralized certificate management system supports HTTPS protocol, making data transfer faster, more secure and more reliable.
The weight configuration feature accelerates backend CVMs request processing speed. The weight of a backend CVM can be set to an integer between 1 and 100 and it is set to 10 by default. The traffic is distributed to different backend CVMs by CLB based on the set weights or the hash and polling results of the access source IP addresses. Higher weights can be set for CVMs with higher specs (such as CPU and memory performance), so that they can take on more requests.
The application-based CLB layer 7 protocol provides content-based routing, which supports user-defined domain names/URLs and custom forwarding rules and groups and enables distribution of requests to backend CVMs under different forwarding rules. CLB can be used to divide the target groups to achieve business separation, which greatly improves service efficiency.
The application-based CLB layer 7 protocol supports custom redirection (rewrite), which solves two major problems:
- Forced HTTPS: When a PC or mobile browser accesses a web service with an HTTP request, an HTTPS response is returned to the browser after the request passes through the CLB proxy, forcing the browser to access the webpage using HTTPS.
- Custom redirection: Redirection is necessary when the web service needs to go offline temporarily in situations such as sold-out events for ecommerce websites, or when the site needs to undergo maintenance, update or upgrade. If no redirection is performed, the old address saved in the user’s bookmarks and search engine database will return a "404" or "503" error page, degrading the user experience and resulting in additional traffic loss.
CLB supports three scheduling algorithms (weighted round robin, IP hash and weighted least connections) and can set the weightage of backend CVMs to ensure even traffic scheduling and improve CLB performance. In addition, the scheduling algorithm of least connections is supported in layer 7 HTTP protocol, which ensures that the load of a backend CVM can be quickly increased when it joins the cluster, reducing the load pressure of other backend CVMs.
For users that use layer 4, CLB provides a simple session persistence function (aka source address-based or IP-based session persistence). When CLB performs load balancing, it uses the source address of the access request as the basis for judging the associated session and forwards all requests from the same IP address (IP address range) to the same CVM. For users that use layer 7, CLB provides a cookie injection-based session persistence method where CLB is responsible for injecting the cookies with no configuration required for the backend CVMs.
CLB checks at a customizable frequency whether the backend CVMs are running normally. When an exceptional CVM is detected, CLB will stop distributing traffic to it and filter out healthy instances to ensure business continuity.
CLB is deployed in multiple availability zones in the same region. For example, two high-performance master/slave clusters can be deployed in Guangzhou Zone 2 and Guangzhou Zone 3 respectively, and when the services in Guangzhou Zone 2 are unreachable, the traffic can be automatically switched to Guangzhou Zone 3, making it easy to cope with faults at the data room level. Combined with the DNS resolution capabilities of DNSPod, CLB can support global load balancing to achieve cross-regional disaster recovery.
- The business has obvious peaks and valleys, and business stability and low costs is desired
- The business goes through significant peaks and troughs, and require flexible control of backend resources.
The business has requirements that are highly time-sensitive. For example, during ecommerce promotion campaigns, web page views may increase by over 10 times in a few hours, and a large number of backend CVMs need to be added when visitor quantity surges. When the traffic drops, the unnecessary CVMs needs to be terminated. CLB can be used to distribute traffic to the business systems, which helps flexibly enhance the service capabilities of the application systems and elastically adjust the backend resources in real time.
- The business has high peak traffic, and needs to build a low-cost architecture.
When a business has high peak traffic, using traditional hardware to build a cluster will be very costly and require tedious OPS work. CLB can work together with the Cloud Monitor to effectively deal with high peak traffic and reduce deployment costs, relieving you from hardware OPS duties and allowing you to focus on developing product features.
- The business has complex modules and requires separation of dynamic and static services
- The business requires separation of dynamic and static services and flexible forwarding
When the number of requests is high, targeted distribution of requests to the website can be achieved by differentiating the static and dynamic requests, effectively reducing the backend load pressure. The dynamic requests can be processed by separately deployed CLB and associated backend CVM clusters, while the static content can be connected to CDN and optimized by COS to significantly improve the loading speed.
- The website or business requires data interconnection
- The business requires content-based routing and forwarding for IP convergence
A large website generally has hundreds of business modules. CLB can analyze HTTP headers by setting different forwarding rules or groups to separate the business modules and achieve content-based routing and forwarding. In addition, custom forwarding paths can be used instead of second-level domain names to reduce the number of DNS polls, converge IP and improve the service accessing speed.
- Direct Connect- hybrid cloud solution achieves stable data transfer and flexible migration
With Tencent Cloud's hybrid cloud solution, the core internal systems and data of the business can be stored in the user-built IDC, and the services can be deployed in the cloud to cope with the surge in user traffic. The stability and speed of in/off-cloud data transfer is ensured by Direct Connect to guarantee data consistency. In addition, the business can be gradually migrated to the cloud through flexible weight configuration, and combined with the data transfer through Direct Connect, an elastic, fast, reliable and low-cost business deployment is easily achieved.
CLB fees consist of instance fees and bandwidth fees generated on real servers. For bill-by-CVM accounts, CLB instance fees are pay-as-you-go and settled daily (24 hours); bandwidth can be purchased with CVMs. Bill-by-IP accounts support two billing modes: monthly subscription and pay-as-you-go. For more information, see Billing Overview.