Server Load Balancer in Networking Services of Alibaba Cloud

Server Load Balancer in Networking Services of Alibaba Cloud

               In this article we will understand Server Load Balancer of Networking Services on Alibaba Cloud. Load Balancer services is available with every public cloud service providers but Alibaba Cloud Server Load Balancer Services having so many other features available for your enterprise level load balancing requirements. Server Load Balancer is basically traffic distribution service that redirect incoming traffic to ECS instances of your Alibaba Cloud to balance the incoming load for internet and intranet service based on that Public IP or Private IP assigned by system so we have both internet facing and private intranet purpose both the load balancing service together. In this we need to configure load balancing forwarding rules to distribute incoming traffic. Alibaba Cloud SLB having more application service capabilities and more enhanced application availability as well. Alibaba Cloud SLB is basically converts available ECS instance backend pool in to High performance and Highly available application service pool by applying virtual service addresses and it distributes the incoming traffic requests to ECS instances in the backend Instance Server pool basis on setted forwarding rules. Alibaba Cloud SLB checks the Health Probe status of available ECS Instances and if it founds unhealthy threshold than automatically isolate that instances to eliminate single point of failure. In addition to that Alibaba Cloud SLB having integrated 5 Gbps DDoS Attack Resistance Service to protect your application services on ECS Instances.

To use SLB we must create at least one listener and two backend pool ECS instances this is minimum. Listener actually checks health of ECS and forwards the requests to the backend ECS Instances. We may have multiple Listeners as well. Alibaba Cloud SLB providing the Layer - 4 Transport Layer (TCP and UDP Protocol) and Layer - 7 Application Layer (HTTP and HTTPS Protocol) Load Balancing Services to user. Transport Layer SLB using the open source software called LVS (Linux Virtual Server) with Keepalived to get load balancing service. And Application Layer (Layer-7) SLB using Tengine (Nginx Based Web Server Project) to get load balancing service.

Alibaba Cloud SLB using Health Check feature which automatically blocked abnormal ECS Instances and redirect requests automatically when they become normal again in that while configuration we need to set threshold to check ECS Instance is normal or not. So, in this case we need to set two threshold unhealthy and healthy threshold in Health Check of SLB. Alibaba Cloud SLB is also supporting Session Persistence feature in which we can set Listener rules to forward same client requests to same ECS Instance until session life cycle of that client with ECS Instance. 

Alibaba Cloud SLB having three routing methods to configure to distribute load towards backend pool ECS instances:

1. Round Robin Routing Method

2. Weighted Round Robin

3. Weighted List Connections

In round robin clients requests are distributed sequentially towards ECS instances backend pool. In Weighted Round Robin Routing Method we can set weight to each ECS Instance like 70-30, 60-40 etc so that higher weighted instances will get more requests out of total incoming requests. In third one Weighted List Connections Routing Method along with the weights we can set number of connections to the instance as well so sometime if both having same weight at any point of time SLB will redirect live connections to instance which having less connections. One more important facility SLB having is URL based routing so that SLB can redirect traffic or requests to backend instance based on URLs. Alibaba Cloud SLB we can configure across multiple zones of the region as well so sometime one zone is performing abnormal that SLB will automatically redirect all traffic to zone 2 which is normal to avoid faulty zones. For security reasons we can also add whitelist IP addresses to our SLB also who can access our Server Load Balancer.

In Layer - 7 Application Layer Server Load Balancer we have centralized certificate management service for HTTPS Listeners by which no need to upload certificates to ECS instances of our backend pool. So cryptographic and deciphering computation CPU overhead is not on ECS instances. Also we have bandwidth peak features by which we can peak bandwidth per listener basis on which type of application service is that is providing by backend pools.

One more added feature in Alibaba Cloud Server Load Balancer is Cross Region Disaster Tolerance, In which we can configure Server Load Balancer instances in different regions and we can add ECS instances in different zones of the regions to server load balancer along with DNS Service. So DNS will resolve the domain name to the IP Addresses of the Server Load Balancer in different regions So, one region become unavailable we can stop domain name resolution for the unavailable region So ultimately our user access to the instances will be not affected. So Alibaba Cloud Server Load Balancer is Cross Region Disaster Tolerance Service.

We also need to take care about default limits while using Alibaba Cloud Server Load Balancer like instance we can have 60 (Default) but if we raise tickets Alibaba Cloud team may enhance it for you. Listener limitation is 50 and at a time we can add and delete maximum 20 instances to our server load balancer.