Building API Gateway Using Ocelot In ASP.NET Core - QoS (Quality of Service)

Catcher Wong

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9 Comments

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Kha Bui3y ago
Thank your articles.
Antariksh5y ago
Thank you for the article. I have a question , If api returning any exception , Ocelot QOS feature is not handling the exception. Can you please clear how we can handle exception using Ocelot and poly.
- Anu Viswan4y ago
  Antariksh I am currently facing the same issue. Did you manage to find a solution for the same with Ocelot-Polly ? "ExceptionsAllowedBeforeBreaking" is not working for this cause.
MJ Ebrahimi6y ago
Good article. For the record, this article was added to this awesome repository. https://github.com/mjebrahimi/Awesome-Microservices-NetCore
Deepak Naidu7y ago
Thanks for the articles that you have on API Gateway, I have a question can I use Ocelot for consuming external APIs provided by 3rd party companies?
- Catcher Wong7y ago
  Of course, API Gateway just forwards the requests to the destination.
ali javany7y ago
Is that working like SSO?
Tridip Bhattacharjee8y ago
When people use api gateways.....in case of micro service ?
- Catcher Wong8y ago
  Not really!! Not micro service can also use API Gateway as well.

Introduction

In the previous articles of this series, we discussed how to build the API Gateway in ASP.NET Core.

And in this article , we will discuss QoS (Quality of Service) module of Ocelot.

If you want to look at the previous articles of this series, please visit the links given below.

What is QoS?

Quality of service is the ability to provide different priorities to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow.

Ocelot uses Polly to achieve this job. And I will use version 4.0.0 of Ocelot to build the following sample.

Preparation

We need to create two projects and ensure that they can run well.

After run them up, we will add configuration of QoS to this route : http://localhost:9000/customers.

Add QoS In configuration.json

We only need to add a node named QoSOptions.

The QoSOptions node contains 3 important properties.

ExceptionsAllowedBeforeBreaking
This value must greater than 0. It means that the circuit breaker will break after a certain number of exceptions occur.
DurationOfBreak
This value specifies how long the circuit breaker will stay open after it is tripped. The unit of this value is milliseconds.
TimeoutValue
This value specifies that a request will automatically be timed out if it takes more than this value. The unit of this value is milliseconds as well.

Here is a sample that shows you how to configure it.

{
"DownstreamPathTemplate": "/api/values",
"DownstreamScheme": "http",
"DownstreamHostAndPorts": [
{
"Host": "localhost",
"Port": 9001
}
],
"UpstreamPathTemplate": "/customers",
"UpstreamHttpMethod": [ "Get" ],
"QoSOptions": {
"ExceptionsAllowedBeforeBreaking":2,
"DurationOfBreak":5000,
"TimeoutValue":2000
}
}
//others.....

The above configuration means that when we visit http://localhost:9000/customers:

If the server does not response for 2 seconds, it will throw a timeout exception.

If the server throws a second exception, the server will not be accessible for five seconds.

Note

There is another property of QoSOptions named TimeoutStrategy. The default value of this property is TimeoutStrategy.Pessimistic. However, at this time, we can not change this value yet.

For showing the result, I made some change on the APIService.