Kestrel now reacts to configuration changes by default

[halter73]

Kestrel now reacts to configuration changes by default

Kestrel now reacts to changes made to the "Kestrel" section of the application's IConfiguration (e.g. appsettings.json) at runtime. To learn more about how to configure Kestrel using appsettings.json, see the appsettings.json example in https://docs.microsoft.com/en-us/aspnet/core/fundamentals/servers/kestrel#endpoint-configuration.

Kestrel will bind, unbind and rebind endpoints as necessary to react to these configuration changes.

Version introduced

ASP.NET Core 5.0.0-preview7

Old behavior

Prior to 5.0.0-preview6, Kestrel did not support changing config at runtime.

In 5.0.0-preview6, you could opt into the now-default behavior of reacting to configuration changes at runtime by binding Kestrel's configuration manually as follows:

webHostBuilder.UseKestrel((builderContext, kestrelOptions) =>
{
    kestrelOptions.Configure(builderContext.Configuration.GetSection("Kestrel"), reloadOnChange: true);
});

New behavior

Kestrel now reacts to configuration changes at runtime by default.

Reason for change

To support reconfiguring endpoints at runtime without completely restarting the server. Unlike with a full server restart, unchanged endpoints are not unbound even temporarily.

Recommended action

For the majority of scenarios where Kestrel's default configuration section does not change at runtime, this change has no impact and no action is needed.

For scenarios where Kestrel's default configuration section does change at runtime and Kestrel should react to it, this is now the default behavior.

For scenarios where Kestrel's default configuration section changes at runtime and Kestrel should not react to it, you can opt out as follows:

webHostBuilder.UseKestrel((builderContext, kestrelOptions) =>
{
    kestrelOptions.Configure(builderContext.Configuration.GetSection("Kestrel"), reloadOnChange: false);
});

Notes

This does not change the behavior of the KestrelServerOptions.Configure(IConfiguration) overload which still defaults to the reloadOnChange: false behavior.

It's also important to make sure the configuration source supports reloading. For Json sources this is done by calling AddJsonFile(path, reloadOnChange: true). This is already done by default for appsettings.json and appsettings.{Environment}.json.

Category

ASP.NET

Affected APIs

• GenericHostBuilderExtensions.ConfigureWebHostDefaults(IHostBuilder, Action) now calls KestrelServerOptions.Configure(IConfiguration, bool) with reloadOnChange: true by default.

This is the discussion issue for the following announcement: aspnet/Announcements#419

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Issue metadata

• Issue type: breaking-change

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