（1） ASP.NET Introduction to core3.1 Ocelot

1. Introduction

Ocelot It was originally designed to be associated with .NET Core Used together , It's a .NET API Gate runner , As usage oriented .NET Perform microservices / Service oriented architecture requires a unified system entry point , That is, when the client （Web Site , Cell phones APP） Etc Web API When ,Ocelot As a unified entry point, it will be distributed to the corresponding API Go to the website （ Address ）. and Ocelot It also integrates a lot of features , Example routing , Certification , Authorization , Speed limit and other function points ,Ocelot The official website also suggests that authentication should be followed by authentication （IdentityServer4） Use it together , Easy integration of bearer tokens . You can go to the official website for details （https://ocelot.readthedocs.io/en/latest/introduction/bigpicture.html） Get to know .
And examine Ocelot Source code , We will see Ocelot It's a bunch of intermediary software in a specific order （Middleware） The pipes that make up .
Ocelot Will HttpRequest The object operates to the state specified by its configuration , Until it reaches the request builder mediation Software , In mediation software, it creates a HttpRequestMessage thing , This object is used to make requests to downstream Services . The intermediary request is made by the software Ocelot The last thing in the pipeline . It doesn't call the next intermediary . Responses from downstream services are stored in the repository for each request scope , And ask to return Ocelot When the pipeline is retrieved . There is a piece of intermediary software that will HttpResponseMessage It's mapped to HttpResponse thing , It is then returned to the client .

2.Ocelot To configure

According to the official website ,Ocelot There are five configurations ：

2.1 Basic integration （Basic Implementation）

When a client visits a downstream service site , Will be unified through Ocelot Gate runner ,Ocelot Gate runner Host The host will first read configuration.json Configuration information , According to the configuration file to find the corresponding downstream service site and return the processing results to the client . This process can be called routing addressing .

2.2 Integrate IdentityServer（With IdentityServer）

When the service site involves authentication and Authorization , It can be done through Ocelot Integrated on the gate IdentityServer, When a client visits a downstream service site , Will pass first IdentityServer After authentication and authorization, they are distributed to downstream service sites .

2.3 Multiple gateways are clustered （Multiple Instances）

Single Ocelot The gate is dangerous , If this gateway goes down , All downstream service sites will be inaccessible , It is impossible to achieve high availability in this way . To solve this problem , You can deploy multiple Ocelot Gateway clustering , and Ocelot Also integrated with load balancer .

2.4 Integrate Consul Service discovery （With Consul）

Check the official website file load balancing column , We know Ocelot Simple load function has been supported , When there are multiple service nodes in the downstream site ,Ocelot Can take on the role of load balancing . But it doesn't provide health checks , The service registration can only be completed by manually adding in the configuration file . It's not flexible enough and there are risks to some extent . At this time we can use Consul To do service discovery , It can relate to Ocelot Perfect combination .

2.5 Integrate Service Fabric（With Service Fabric）

If you are in Service Fabric Central government has a service , The naming service is usually used to access them .

3. Summary

Ocelot The gateway is the system's only access to the outside world , It's like the company's doorman is responsible for addressing 、 Access restrictions 、 Safety check 、 Location guidance and other functions . It also provides routing , Authentication 、 Monitoring 、 Load balancing 、 Get it 、 Request fragmentation and management 、 Static response processing and other functions .Ocelot The key point of the gateway is , All clients and consumers access microservices through a unified gateway , All non business functions are handled at the gateway level . Usually the gateway also provides REST/HTTP Access to API, The server registers and manages services through the gateway . After that chapter , I will continue to base on GitHub Contributors open source projects Ocelot Demo The example describes its functions .Ocelot Demo Address https://github.com/catcherwong-archive/APIGatewayDemo.

References ：
Ocelot Official website