[For AWS beginners] Easy to understand in 5 minutes! Easy-to-understand explanation of Amazon ELB!

2021.06.22

• Server construction/operation
• Infrastructure related
• Shikoku Office

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22,757

Hello! This is Inoue, a Persian cat from Beyond Shikoku Office.

This time, I would like to explain about the [load balancer] provided by AWS!

What is [load balancer]?

A load balancer is something you often hear about, but to put it simply, it is a device that balances (distributes) the load on servers.

If there is not a lot of access and the server handles few requests, there is no problem without using a load balancer. However, suppose that for some reason access becomes concentrated on the server.

At such times, many people may have experienced that the server becomes heavy and it takes a long time to display the site.

When a server is accessed from the Internet, the server processes the request using resources such as the CPU and memory installed on that device.

If for some reason access becomes concentrated and the number of requests increases rapidly, the page may become slow to display on the web user's browser or may not be displayed at all. A high load condition occurs when request processing is delayed, such as when this page is slow to display or not displayed at all.

It can be said that the load is high due to concentrated access to the server.

A load balancer plays an active role in preventing sites from displaying too slowly or not being displayed under such high load conditions.

By distributing the load across multiple servers, you can prevent the load from concentrating on one server.

The load balancer mechanism not only concentrates web access, but also provides stable services to web users even in the event of a server failure.

The load on the server cannot always be said to be constant. Therefore, in order to always provide stable services to users, it is necessary to introduce a load balancer.

What is [ELB]?

ELB is an abbreviation for [Elastic Load Balancing] and is a load balancer provided by AWS.

As mentioned above, a load balancer is a mechanism that distributes the access (traffic) concentrated on a server to multiple servers or networks to distribute the load. It is also called a "load balancer" because it distributes a single load.

In addition to load balancing, it also has a health check function. The health check feature allows you to monitor server performance in real time.

This allows you to stop sending traffic to an abnormal server when it is found, and send traffic to other healthy servers for load balancing.

ELB automatically distributes the load and prevents servers from going down.

Furthermore, ELBs automatically scale according to load conditions, so administrators (engineers) do not have to manually increase the number of ELBs or raise their specs.

If you anticipate a sudden increase in traffic, such as a sudden increase in access, you can also use it in conjunction with AWS Auto Scaling. This allows you to increase or decrease the number of servers according to the amount of requests, and prevent server downtime.

Additionally, as a feature of ELB, it is possible to load balance the traffic of installed EC2 even if the availability zones are different.

We recommend that you enable multiple Availability Zones for all your load balancers.
However, your Application Load Balancer requires at least two Availability Zones to be enabled.
This configuration allows your load balancer to continue routing traffic.
If one Availability Zone becomes unavailable or there are no healthy targets, your load balancer can route traffic to healthy targets in another Availability Zone.

Reference site: How ELB works

■Types of ELB
There are three types of ELB: ALB, NLB, and CLB.

In addition to the three typical AWS ELBs mentioned above, there is also [GLB].

GLB is an abbreviation for [Gateway Load Balancer].

Gateway Load Balancer allows you to easily deploy, scale, and run third-party virtual network appliances.
Gateway Load Balancer, which provides load balancing and auto scaling for a fleet of third-party appliances, is transparent to the source and destination of traffic.
This feature makes it ideal for working with third-party appliances for security, network analysis, and other use cases.

Reference site: Elastic Load Balancing

It's a service that has just been released, so I'd like to write a separate blog after studying it!

By the way, when I tested ALB to write this blog, I found that
if I just linked the ALB to the verification instance, a "403" status code was returned when I checked the access log.

172.31.4.72 - - [15/Jun/2021:07:59:03 +0000] "GET / HTTP/1.1" 403 4897 "-" "ELB-HealthChecker/2.0"

In that case, I placed an "index.html" file under the document root, put the words "aws test" in the file, and when I accessed it from a browser, a "200" status code was returned successfully.
*This requires that apache be installed on the server.

First, move to the document root.

[root@ip-172-31-38-25 httpd]# cd /var/www/html

Create a file called "index.html".

[root@ip-172-31-38-25 html]# touch index.html

Write "aws test" in the "index.html" file you created.

[root@ip-172-31-38-25 html]# vi index.html

If you want to access the verification instance from your browser, you can do so by entering [Public IPv4 address] in the chrome search bar.

Let's check the access log again!

172.31.4.72 - - [15/Jun/2021:08:38:35 +0000] "GET / HTTP/1.1" 200 9 "-" "ELB-HealthChecker/2.0"

The status code has now become ``200'' and when you check the ``Target Group'' from the AWS console, the status of the ``Target Group'' has also changed from Unhealthy to Healthy!

summary

For example, a load balancer is

“This is your job.” “I want you to do this job.”

It is like a boss (control tower) in a company.

By using a load balancer wisely, you can prevent server downtime and eliminate problems such as site display delays and ``site not displaying,'' which will likely increase trust in your site.

I also want to become a person who can work as a load balancer.

Growing every day, moving forward every day.
I have to update myself every day! ! !
Thank you for reading to the end.

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