Introduction to BigIP F5 Load Balancer

With the advent of the cloud, infrastructure provisioning has become extremely fast and the horizontal scalability of the application has become necessity to improve the site performance and availability. To serve the incoming traffic in an optimum way, Load balancer is used on top of the application servers. The load balancer is the device that acts as the reverse proxy and distributes network or application traffic across number of servers. Load balancer will route the traffic to the servers and will be responsible to distribute the traffic such a way that application experience will enhance. There are multiple load balancing solutions available such as AWS provided ELB(Elastic load balancer), HA proxy servers, F5 etc. Big IP is load balancing solution by F5 networks. There are two types of load balancing modules by F5 networks,

• Local Traffic Manager (LTM): Local load balancing based on a full-proxy architecture
• Global Traffic Manager (GTM): Global server load balancing using DNS

Before deep diving into the BigIP LTM and it’s architecture on AWS, Let’s go through the basic terminology used for the F5,

1. Node – Represent physical or virtualized servers where the service or application runs. For eg: a web server or ec2 server running apache/nginx
2. Pool – Is a collection of nodes. Pool constantly monitor the nodes for their availability and if any node is not reachable then it marks that node as unavailable. For eg: pool can have multiple web servers
3. Virtual Server – Each virtual server has an associated pool with a protocol defined. Each virtual server will have different IP linked to them. These IP’s are called as VIP. For eg: WS_Http and WS_Https may be two virtual servers linking to the same pool with 2 different protocols and IPs defined.
4. Health Monitor – Monitor health and performance of nodes that are members of the pool. It verifies connections on pool members and nodes and are configured in the pool. For eg: HTTP health monitor, for HTTP health verification of a server.
5. iRules – Implement business logic into your network layer by simple scripting and that is iRules. For eg: You can configure to redirect HTTP requests automatically to HTTPS with iRules.

f5 load balancer also has an option to import SSL certificate, thereby avoiding a scenario to upload the same to all the servers. Similar facility is available for ELB as well. Below is the high level architecture of F5 setup, In the above setup:

There are three nodes under pool web and two db servers under pool DB

There are three virtual servers,

1. http virtual server for distributing http traffic
2. https virtual server for distributing https traffic and
3. for handling db requests

How F5 functions,

All the public request will hit the LTM load balancer and according to iRules, the virtual servers will be selected. Virtual server will pass the request to the associated pool and pool will apply routing algorithm and checks for the healthy node within the pool to route traffic to.

Below are the algorithms which can be selected to select the node,

1. Round Robin – Default balancing method. Requests are passed to the next server in line, distributing the connections equally across an array of servers.
2. Least Connections – Requests are simply passed to the node that has the least number of current connections.
3. Observed – Difference between least connection and observed is that the least connection method measures connections only at the time of load balancing whereas observed method tracks layer 4 connections count and creates a ratio.
4. Predictive – Uses same approach of observed, where nodes are rated based on number of current connections. With this method f5 system analyzes the performance of nodes, whether it is improving or declining. Performance improving nodes receive a higher proportion of connections.

This is the first post of F5 series, upcoming blog posts would be,

Step by step guide to launch AWS infrastructure for F5 Load balancer,

Below is the architecture of F5 on AWS. Will discuss this architecture in next blog post.

Configure the F5 Load balancer instance

Automate the infrastructure provisioning of BigIP F5 Load balancer on AWS

Difference between LTM and GTM module of F5

If you have any queries or wish to talk more about this architecture/setup or any of the technologies involved, you can mail me at nikunjs@cloudthat.in. Follow me @NikunjShukla.

WRITTEN BY CloudThat