Introduction to HTTP(S) Load Balancing

Lab Details:

  1. This lab walks you with a demo of the HTTP Load Balancer.

  2. In this lab, we will discuss different types of Load Balancer.

  3. Duration: 60 minutes

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What is HTTP(S) Load Balancer?

  • Before understanding details about HTTP(S) load balancing, let us try to understand the architecture behind networking, which is based on the OSI model. You might have heard it before also but today we will discuss the OSI model at a high level. It'll help you understand things easily.

  • We have 7 layers in the OSI model, which goes from bottom to top from the sender's end and top to bottom at the receiver's end.

  • Layer 1 - Physical Layer, which is your actual cables

  • Layer 2 - Data Link Layer, which will provide you a physical non-changing address called MAC Address, The data link layer translates the physical's raw bit stream into Frames. Basically, Frames are a serial collection of bits. Header and trailer to the frame at this layer. The header which is added to the frame contains the hardware destination and source address called MAC Address.

  • Layer 3 - Network Layer, A Network layer adds the source and destination address to the header of the frame. Addressing is used to identify the device on the internet which is called IP Address. 

  • Layer 4 - Transport, This layer can be termed as an end-to-end layer as it provides a point-to-point connection between source and destination to deliver the data reliably. It adds Port to the packets. To understand in a better way, Suppose you have a lot of processes running on your system like Google, Amazon, Yahoo, etc. Actually, your system as a client is trying to communicate with these servers to take your segment to the correct process on that server and bring that back response to the correct process on your computer, it happens using Port Numbers which help you determine which request belongs to which process. Think IP address as your Society and Port number as your House number.

  • Layer 5 - Session layer which is used to establish, manage, and terminate the session

  • Layer 6 - Presentation layer which is used to translate, encrypt and compress data.

  • Layer 7 - Application layer which is used to allow access to network resources.

  • Load Balancing can be done using different methods, i.e. Layer 4 — TCP, UDP, and Layer 7 — HTTP, HTTPS 

  • We are discussing common facts about all Layer 7 Load Balancers(LBs) and Layer 4 Load Balancers(LBs). In the demo, we will create a simple HTTP Load Balancer. You can create HTTPS Load Balancer in case you own a domain, we have attached a document on how to do that as well.

  • Layer 4-LBs act almost as transport layer aware routers that do no packet manipulation and are faster than Layer 7-LBs that perform a number of manipulation to packets and also have session affinity feature ensuring connections that result from the same source are always served from the same backend. Layer 7-LBs are more common and are often always software whereas Layer 4 - Load Balancers are less common, and tend to be implemented in dedicated hardware.

  • One important note about Layer 7-LBs is their ability to terminate the SSL traffic. This is a limitation for most Layer 4-LBs as they cannot determine if incoming packets are wrapped in SSL and therefore fail to terminate SSL traffic. L7 Load Balancers can have CA certificates installed within them that can verify the authenticity of the service instead of storing and handling them backends. The processing strain from having to encrypt and decrypt such requests is pushed onto Layer 7 - Load Balancers to decrypt such data and re-encrypt the packet for transmission to the backend server. This often results in high latency and can be problematic at times.

  • Within Layer 7 - Load Balancers, the packet is inspected, although this can be a costly process in terms of latency, it has additional features like balance traffic based on content. For example, your company has a pool of backends that have been fitted with some high-end instances optimized for video processing. Another pool may contain low-power CPUs that are optimized for static websites. Layer 7 - Load Balancers can use the URL path e.g. to serve the most appropriate backend to send incoming traffic to the ones with high-end instances, whereas requests to a different URL such as can be transferred to the low-power instances, all thanks to the Layer 7 - Load Balancers ability to intelligently split traffic.

  • Another interesting feature of Layer 7 - Load Balancers is the fact of session affinity or connection stickiness. It is the tendency for a connection where the traffic from the same source continues to be served from the same backend. So if your IP is and you connect to Youtube servers, that are configured with Layer 7-LBs, there is a high chance your tutorial on 'How to get GCP Certified Profession', is being served by the exact same server even if you switch to any other video. This way you receive an uninterrupted consistent connection, which improves the quality of service. Session affinity provides a best-effort attempt to send requests from a particular client to the same backend for as long as the backend is healthy.

Architecture Diagram:


Simple HTTP Load Balancing (click to enlarge)

The flow of the above diagram explained below:

  1. An IPv4 user sends a request to the Public IP provided in the forwarding rule.

  2. The forwarding rule then directs the request to the target HTTP proxy.

  3. As we are using a Simple host and path rule, the target proxy determines that the single backend service receives all requests.

  4. The load balancer then determines the instance group and directs the incoming request to the VM instance in the group.

  5. Finally, the VM instance responds to the request by the user.

Lab Tasks:

  1. Login into GCP Console.

  2. Creating an Instance Template.

  3. Creating an Instance Group.

  4. Creating a Firewall Rule.

  5. Reserving an External IP address.

  6. Creating Target pools.

  7. Creating forwarding rules.

  8. Creating a health check.

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