Redirect to secondary host when primary host is unavailable in Ocelot API Gateway (C#, .NET Core, Ocelot)

Question

I would like to use Ocelot API Gateway to connect services, but if the primary host is unavailable it needs to redirect to secondary host.

For example in below configuration i have two ports one is 5023 and 5102, So when 5023 is unavailable i want it to redirect to 5102.

Please help, Thanks in advance.

configuration.json

{
  "Routes": [
    {
       "DownstreamPathTemplate": "/GetProductDetails",
       "DownstreamScheme": "http",
       "DownstreamHostAndPorts": [
         {
           "Host": "localhost",
           "Port": 5023
         },
         {
           "Host": "localhost",
           "Port": 5102
         }
       ],

       "UpstreamPathTemplate": "/",
       "LoadBalancerOptions": {
         "Type": "RoundRobin" 
       },
      "UpstreamHttpMethod": [ "GET" ]
    }
  ]
}

Program.cs

using Ocelot.DependencyInjection;
using Ocelot.Middleware;

var builder = WebApplication.CreateBuilder(args);

builder.Configuration.AddJsonFile(
"configuration.json",optional:false,reloadOnChange:true);

builder.Services.AddOcelot(builder.Configuration);

var app = builder.Build();


app.MapControllers();

var ocelotConf = new OcelotPipelineConfiguration()
{
    PreErrorResponderMiddleware = async (context, next) =>
    {
        if (context.Response != null)
        {

        }
        await next.Invoke();
    }
};

await app.UseOcelot(ocelotConf);

app.Run();

Either can we write custom load balancer?

Answer 1

Finally after thinking so much i have understood that from request pipeline we can process to next invoke if the current host is not active.

Code is below.

var ocelotConf = new OcelotPipelineConfiguration()
{
    PreErrorResponderMiddleware = async (context, next) =>
    {
        // Initial invoke
        await next.Invoke();
        if (context.Response != null)
        {
            // Checking if the initial invoke is throwing 502
            //(Means service is down)
            if(context.Response.StatusCode == 502)
            {
                // If service is down forwarding to next host
                await next.Invoke();
            }
        }
    }
};

await app.UseOcelot(ocelotConf);