Winton.Extensions.Configuration.Consul

Adds support for configuring .NET Core applications using Consul. Works great with git2consul.

Installation

Add Winton.Extensions.Configuration.Consul to your project's dependencies, either via the NuGet package manager or as a PackageReference in the csproj file.

Usage

Minimal Setup

The library provides an extension method called AddConsul for IConfigurationBuilder in the same way that other configuration providers do. The IConfigurationBuilder is usually configured in either the Program or Startup class for an ASP.NET Core application. See Microsoft's documentation for more information about IConfigurationBuilder.

A minimal example is shown below:

var cancellationTokenSource = new cancellationTokenSource();
builder
    .AddConsul(
        $"{env.ApplicationName}/{env.EnvironmentName}",
        cancellationTokenSource.Token);

Assuming the application is running in the 'Development' environment and the application name is 'Website', then this will load a JSON configuration object from the Website/Development key in Consul.

The CancellationToken is used to cancel any active requests/watches to/on Consul. It is recommended that this is cancelled during application shutdown to clean up resources. This will typically be done in one of two places. Either in the Program class, for example:

public static void Main(string[] args)
{
    var cancellationTokenSource = new CancellationTokenSource();
    WebHost
        .CreateDefaultBuilder(args)
        .ConfigureAppConfiguration(
            builder => builder.AddConsul("key", cancellationTokenSource.Token))
        // Rest of webhost setup
        .Build()
        .Run();
    cancellationTokenSource.Cancel();
}

Or in the Startup class, for example:

public Startup()
{
    _cancellationTokenSource = new cancellationTokenSource();
    var builder = new ConfigurationBuilder()
        .AddConsul("key", _cancellationTokenSource.Token);
    Configuration = builder.Build();
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env, IApplicationLifetime appLifetime)
{
    // Other app configuration

    appLifetime.ApplicationStopping.Register(_cancellationTokenSource.Cancel);
}

Options

AddConsul has an overload with an additional third parameter of type Action<IConsulConfigurationSource> which allows the options outlined below to be set.

• ConsulConfigurationOptions

  An Action<ConsulClientConfiguration> that can be used to configure the underlying Consul client.

• ConsulHttpClientHandlerOptions

  An Action<HttpClientHandler> that can be used to configure the underlying Consul client's HTTP handler options.

• ConsulHttpClientOptions

  An Action<HttpClient> that can be used to configure the underlying Consul client's HTTP options.

• OnLoadException

  An Action<ConsulLoadExceptionContext> that can be used to configure how exceptions thrown during the first load should be handled.

• OnWatchException

  A Func<ConsulWatchExceptionContext, TimeSpan> that can be used to configure how exceptions thrown when watching for changes should be handled. The TimeSpan that is returned is used to set a delay before retrying. The ConsulWatchExceptionContext provides data that can be used to implement a backoff strategy or to cancel watching altogether.

• Optional

  A bool that indicates whether the config is optional. If false then it will throw during the first load if the config is missing for the given key. Defaults to false.

• Parser

  The parser to use, which should match the format of the configuration stored in Consul. Defaults to JsonConfigurationParser. Either use those under Winton.Extensions.Configuration.Consul.Parsers or create your own by implementing IConfigurationParser.

• ReloadOnChange

  A bool indicating whether to reload the config when it changes in Consul. If true it will watch the configured key for changes. When a change occurs the config will be asynchronously reloaded and the IChangeToken will be triggered to signal that the config has been reloaded. Defaults to false.

Storing Config as Expanded Keys In Consul

By default this configuration provider will load all key-value pairs from Consul under the specified root key, but by default it assumes that the values of the leaf keys are encoded as JSON.

Take the following example of a particular instance of the Consul KV store:

- myApp/
    - auth/
        { 
            "appId": "guid",
            "claims": [
                "email",
                "name"
            ]
        }
    - logging/
        {
            "level": "warn"
        }

In this instance we could add Consul as a configuration source like so:

var configuration = builder
    .AddConsul("myApp", cancellationToken)
    .Build();

The resultant configuration would contain sections for auth and logging. As a concrete example configuration.GetValue<string>("logging:level") would return "warn" and configuration.GetValue<string>("auth:claims:0") would return "email".

Sometimes however, config in Consul is stored as a set of expanded keys. For instance, tools such as consul-cli load config in this format.

The config in this case can be thought of as a tree under a specific root key in Consul. For instance, continuing with the example above, the config would be stored as:

- myApp/
    - auth/
        - appId/
            "guid"
        - claims/
            0/
                "email"
            1/
                "name"
    - logging/
        - level/
            "warn"

As outlined above this configuration provider deals with recursive keys by default. The only difference here is that the values are no longer encoded as JSON. Therefore, in order to load this config the parser must be changed. This can be done like so when adding the configuration provider:

builder
    .AddConsul(
        "myApp",
        cancellationToken,
        options =>
        {
            options.Parser = new SimpleConfigurationParser();
        });

The SimpleConfigurationParser expects to encounter a scalar value at each leaf key in the tree.

If you need to support both expanded keys and JSON values then this can be achieved by putting them under different root keys and adding multiple configuration sources. For example:

builder
    .AddConsul(
        "myApp/expandedKeys",
        cancellationToken,
        options =>
        {
            options.Parser = new SimpleConfigurationParser();
        })
    .AddConsul("myApp/jsonValues", cancellationToken);