Graceterm

Graceterm is a AspNet Core middleware wich provides implementation to ensure graceful shutdown of the application. It was originally written to get zero downtime while performing Kubernetes rolling updates. The basic concept is: After aplication received a SIGTERM (a signal asking it to terminate), graceterm will hold it alive till all pending requests are completed or a timeout ocurr.

If you're interested in configuring aspnet core app on a Kubernetes cluster to get zero downtime updates and wondering about what needs to be done, take look at https://github.com/mnconsulting/graceterm/wiki/Zero-downtime-AspNet-Core-and-Kubernetes-rolling-updates.

Usage

Install Nuget package: Graceterm

Considering a standard AspNet Core application, edit Configure method of Startup by adding app.UseGraceterm() invocation. The graceterm should be on top of request pipeline to work properly, this means that you must add the app.UseGraceterm() invocation before any other app.UseSomething(). If you are using a custom logging configuration, you should put the code wich configures log before the app.UseGraceterm() in order to Graceterm generate logs according to your preferences.

using Graceterm;

public class Startup
{
    ...
    
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ...)
    {
        //
        // Custom logging configuration goes here.
        //

        // Add graceterm just after logging configuration and before 
        // any other middleware.
        app.UseGraceterm(); 

        app.UseOtherMiddleware();       
        ...
    }
    ...
}

Options

You may customize Graceterm behavior providing a delegate to app.UseGraceterm(delegate) invocation. The available options are describled bellow:

app.UseGraceterm(options => 
{
    // Timeout
    // How much time Graceterm will hold application alive (default is 60 seconds)
    options.TimeoutSeconds = 15; 
    
    // IgnorePaths
    // Requests to paths starting with the segments ("/path1", "/path2" and "/path3") 
    // will not be handled by Graceterm.
    options.IgnorePaths("/path1", "/path2", "/path3");
    
    // UseCustomPosSigtermIncommingRequestsHandler
    // By default graceterm send a 503 response, with a "503 - Service unavailable" text body 
    // for requests initiated after application has asked to terminated. You may modify this
    // behavior by providing a Func<HttpContext, Task> to handle this requests.    
    options.UseCustomPostSigtermIncommingRequestsHandler(async (httpContext) =>
    {
        httpContext.Response.StatusCode = 503;
        await httpContext.Response.WriteAsync("My custom message!");
    });
});

Contribute

Issues and pull requests are welcome.