Load Balancing in Amazon Web Services

Load balancing is one of the most important technique to be followed for architecting highly scalable and available applications on AWS cloud. Keeping this in mind, I have compiled my experience and articles i have written on this subject as "Load balancing on AWS" series.  

Dissecting Amazon Elastic Load Balancing : Amazon ELB is dissected into 18+ points and analysed based on the production implementation experience. This article is a must read for all Amazon ELB users who wants to understand in detail what ELB can do and what are some of the road blocks you can face sometimes when using Amazon ELB. Click here for the article.  

Amazon ELB Multi region migration checklist: Amazon Elastic Load Balancing has a Amazon EC2 Regional scope. It needs to be migrated to alternate Amazon EC2 region in event of DR or during new migration setup . I am sharing my experience in this post as few checklists/areas that needs to be taken care during this Amazon ELB migration to alternate EC2 region. Refer Article

Amazon ELB Implementation Architectures : Amazon ELB can be implemented in variety of architectures in your AWS cloud. Some of them are real bad cases and some of them follow best practices. If you want to understand the common implementation architectures and its pro's/con's refer this article  

Comparison Analysis between Amazon ELB and HAProxy:  HAProxy is a popular OSS software load balancer widely used in Amazon Cloud Infrastructure. This article provides a detailed comparison between the two and analyzes where both of them stand. This article is featured in the HAProxy web site as well. Click here for the article

Architecting High Availability @ HAProxy Load Balancing Tier: Not all the times Amazon ELB is used as the choice of load balancer in Amazon Web Services. But deploying an OSS load balancer in AWS has got is own set of considerations and high availability is one of them. In this post i explore how to design High Availability @ HAProxy load balancing layer. Refer Article

Architecting Highly Available Web App Layer using HAProxy Load Balancing : In this post we explore four options of Load balancing Web/App Tier using HAProxy in AWS. Refer Article

Configuring Citrix NetScaler Load Balancing on AWS: Citrix NetScaler is a popular Load balancer in the Enterprise world. Hardware and virtualized NetScaler has been serving many popular enterprise online assets for years. How to configure Citrix Netscaler based Load Balancing in AWS is explained in this post. Refer Article

Load Balancing Amazon RDS Read Replica's using HAProxy: In this post, let us explore how HAProxy can be used to solve load balancing between RDS Read Replica's in Amazon Cloud.Refer Article

Choosing right HAProxy- Amazon EC2 Instance Types and AMI Types for load balancing: Before choosing optimal Amazon EC2 instance Type for HAProxy Load balancing layer in AWS we need to minimum understand some important factors involved. Refer Article 

Configuring Amazon ELB and understanding the parameters in detail: Amazon provides a detailed documentation on how to configure ELB. In this article i have detailed the configuration steps with detailed understanding on the parameters and its implications. Must read of Amazon ELB newbies. Click here for the article 

Web Session Synchronization patterns in AWS: Architectures for synchronizing sessions of load balanced Web/App EC2 is detailed in this post. Refer Article

Geo Distributed Load Balancing using Route53 and Amazon ELB: Some customers would have Geo Distributed their architecture across multiple Amazon EC2 regions. In this article we explore why do we need Geo Distributed architecture, Cost of Latency and how to achieve it using Route 53 + Amazon ELB. Click here for the article

Deeper Health Checks and Problems in Load Balancing in AWS: Health Checks are one of the essential mechanisms that helps you to keep N-Tiered system highly available.This sounds simple and straight forward right, but some of the customers i have consulted follow a much deeper Health check diagnostic mechanism and it might have problems when migrated to AWS cloud. Let us explore this case in detail in this post. Refer Article

Configuring Amazon ELB With SSL offloading: How to configure SSL with Amazon ELB. Click here for the article What are the benefits of offloading SSL in Amazon ELB. Here

Monitoring Amazon ELB using Amazon CloudWatch and understanding the result and metrics

Why do we need Amazon Elastic Load Balancing and What are its benefits ?

Configuring Citrix NetScaler Load Balancing on AWS

Citrix NetScaler is a popular Load balancer in the Enterprise world. Hardware and virtualized NetScaler has been serving many popular enterprise online assets for years. NetScaler supports many load balancing algorithms like (Round robin, Least connection, source IP Hash etc..) + comes with many more features. Citrix Netscaler with its powerful load balancing capabilities serves many websites under it inside an enterprise setup. Citrix NetScaler is usually preferred in AWS by :

• Enterprises which already have some partnership with Citrix and have some form of NetScaler licenses / agreements with Citrix
• Enterprises which want proper support for their load balancing tier which other OSS LB providers were not able to meet
• Enterprises which already have trained IT staff in Citrix products including NetScaler and do not want change
• Enterprises which wants Load balance tier to provide them with Security, Performance in addition to wide variety of LB options.

In this article i am going to share the experience on configuring Citrix NetScaler in AWS cloud. Citrix NetScaler will be used inside public subnet of Amazon Virtual Private Cloud (VPC) and will load balance requests between 2 web/App EC2 instances running in private subnet of the Amazon VPC. The Web/App amazon EC2 are deployed in multiple subnets in Multi-AZ architecture inside the Amazon VPC. 

Following is the step by step configuration details for the same:

Step 1: Login to AWS market place using the console using IAM user account and Click Amazon EC2 tab and Click the Launch Instance option.

Step 2: Find the Citrix NetScaler Instance and choose the right instance based on your application load and features needed. For example:  if your application load will not exceed 10 Mbps and you need round robin load balancing, you can choose NetScaler Standard Edition 10 Mbps as your instance type. If your application has heavy load and you are planning to leverage other features of Netscaler like performance, security etc, you can choose NetScaler VPX Platinum Edition - 1000 Mbps option as well. To know more about Citrix NetScaler on Amazon refer link https://aws.amazon.com/marketplace/seller-profile?id=fb9c6078-b60f-47f6-8622-49d5e1d5aca7

Step 3: Click “Launch with EC2 Console” option and launch the Citrix NetScaler in suitable+available Amazon EC2 region of your choice.

Step 4: Select Amazon VPC IP range example: 10.100.0.0/16 in our case, choose the public subnet for Citrix NetScaler EC2 instance and launch the EC2 Instance as shown in the below screen shots.

Step 5: Once the Instance status is “2/2 check passed”, attach one Amazon Elastic IP to Citrix NetScaler default ENI- Elastic Network Interface.

Step 6: Use the Amazon Elastic IP in your browser.Use the default user name and password “nsroot” and login into Citrix NetScaler console.

Step 7:Click configuration tab -> expand the Network and add the IP address  (The virtual IP address you have to configure for the load balancing)

Step 8: Expand the system option on the left panel and click the settings and click the “configure basic features” settings on the right panel. Citrix NetScaler offers many features like :

• Integrated Caching, HTTP compression SSL offloading for performance
• Content Filtering, Access Gateway, App Firewall, Authentication etc for Security

In this post we are going to explore only Load balancing feature, so select the “Load Balancing” and click OK.

Step 9: Select and expand the load balancing feature on the left panel and click the services.

Step 10: Click the “Add” button and give the web/app EC2 instance details to be load balanced. We have two Web/App EC2 with 10.100.5.15 and 10.100.4.15 in two subnets in Multi-AZ architecture. Both these web/app ec2 are attached to the NetScaler for Load Balancing. Illustrated in below screenshots.

Click “Create” , then check the service status is “UP”

Step 11: Click the “Virtual Servers” on the left panel.Type the Virtual Server name and the IP address, protocol and port number. Then select the service for the Web/App EC2 Servers.

Step 12: Select the “method assistance” tab and select the load balancing algorithms.   
The load balancing algorithm defines the criteria that the NetScaler appliance uses to select the service to which to redirect each client request. Different load balancing algorithms use different criteria. For example, the least connection algorithm selects the service with the fewest active connections, while the round robin algorithm maintains a running queue of active services, distributes each connection to the next service in the queue, and then sends that service to the end of the queue. Some load balancing algorithms are best suited to handling traffic on websites, others to managing traffic to DNS servers, and others to handling complex web applications used in e-commerce or on company LANs or WANs. The following table lists each load balancing algorithm that the NetScaler appliance supports, with a brief description of how each operates.

LEASTCONNECTION: Which service currently has the fewest client connections. This is the default load balancing algorithm.

ROUNDROBIN:Which service is at the top of a list of services. After that service is Selected for a connection, it moves to the bottom of the list.

LEASTRESPONSETIME: Which load balanced server currently has the quickest response time.

URLHASH:A hash of the destination URL.

DOMAINHASH:A hash of the destination domain.

DESTINATIONIPHASH:A hash of the destination IP address.

SOURCEIPHASH:A hash of the source IP address.

SRCIPDESTIPHASH:A hash of the client's IP address and port.

LEASTBANDWIDTH:Which service currently has the fewest bandwidth constraints.

LEASTPACKETS:Which service currently is receiving the fewest packets.

CUSTOMLOAD:Data from a load monitor.

TOKEN:The configured token.

LRTM:Fewest active connections and the lowest average response time.

The default is “least connection”.For simplicity purpose choose for “Round Robin” as your Load Balancing method for this post.

Then click create and check the status of the Virtual servers is “UP”. Note the method now is displayed as Round Robin.

Step 13: Now that the simple Load balancing configuration is completed in Amazon VPC, let us do a simple testing of our config till this stage. Go to the web browser in the Jump box provisioned in the VPC. Use the Virtual Server IP address of the Load balancer and check whether the web application is accessible

Step 14: In case you want to check the client request details, Login to NetScaler in CLI mode. Use the following command ”stat lb vserver NS-LB01”

Before user access the web application, load balancing service status is as follows:

After user accessed the web application, load balancing status is as follows:

Step 15: How to access the web application in public Internet ? Select the NetScaler Instance in EC2 console and select the “Managed Private IP Address” option.

Step 16: Click the “Assign a secondary private address” option and enter the IP Address and click the “Yes Update” option.

Step 17: Then go to Elastic IP window, select the Elastic IP Address (EIP) and right click the EIP and select the “Associate IP Address” 

Step 18:Select the NetScaler Instance on the “Instance” option, Select the IP Address from “Private IP Address” option and Click “Yes Associate”. The EIP will attach with the Secondary IP Address of NetScaler Instance.

Now Use the Elastic IP (Example: 54.244.36.218) in your browser and access your application from Public Internet.

AWS Performance Tip 2: Use Page Cache-Web Accelerators to reduce Latency

Tip : Deliver your content from the edge of your architecture stack.
Imagine you have online application with Multi-tiered architecture comprising of Security Tier, Load Balancing Tier, Web tier, Application tier and Caching tier etc. Information has to travel through all these tiers to hit the caching layer and deliver the response back many times. This might take couple of hundred's of milliseconds sometimes depending upon the processing needs and network latency in the AWS infra . This overall latency might not be acceptable for certain use cases which needs sub second content delivery to the end users. 
Instead of delivering your frequently accessed contents from the deep caching tier, You can re-architect your stack a little and try to deliver content from entry point itself. Solutions like Varnish, aiCache and NetScaler specialize in this caching and acceleration techniques and are widely used in AWS infra by architects. AMIs of these products are available on the AWS marketplace and many customers have already put them on production use. These products have the capability to cache/compress pages, objects, URL etc and by placing them at the entry of your architecture you will reduce the latency, save precious back end compute cycles and save costs by reducing the instance capacity needed at the backend.  In case you use NetScaler Amazon EC2 it comes with sophisticated Load balancing algorithms as well, this way you can cut an extra LB tier and merge both cache+LB together to achieve high performance at low latency. Since these products are at the entry and have heavy dependency on bandwidth and memory, it is recommended to use EC2 instances with High IO and Memory capacity for these products. 
This architecture implementation is a useful technique and can be widely adopted on segments like online newspapers/news, blogs ,content management systems, online classifieds use cases etc in AWS, which has lots of static content that does not change quite frequently and can be delivered again and again from the page cache-web accelerators tiers itself. 

Related Articles :

Cost of Latency and Route53 LBR
Varnish Deployment Architectures in AWS