Is it possible to use aspire/service discovery to get a url by the service name (locally/production)

[mip1983]

Hi there,

With service discovery in aspire it's easy to give resources references to each other and register http clients that resolve to a particular app.

Is there a way to leverage it in other places to get a url to a service, particularly between web apps? I'm thinking for example if I've got identity server and a web app using it:

    var identity = builder.AddProject<Projects.Identity>("identity").WithExternalHttpEndpoints();

    var web = builder.AddProject<Projects.Identity>("web")
            .WithExternalHttpEndpoints()
            .WithReference(identity);

     identity = identity.WithReference(web);

Where I have to configure things like 'authority' and 'redirectUri' etc. (on both ends) , can I get these Uri's via aspire/service discovery?

I can see it does add urls to configuration in the 'services' section, so I can pull things out via IConfiguration (don't know if there's a neater mechanism?). But, when deployed to Azure container apps, these config urls aren't to the custom binding that I've applied to the container app (just the generic/random Azure assigned ones, I've not put a wildcard binding at the cae level). Is there a way for it to know about these and fetch via some service discovery mechanism?

[mmacneil]

Did you ever find a solution for this @mip1983 ? I have the identical scenario and suspect many others would as well... seems like something that should be supported.

[davidfowl]

You can just read the format described here https://learn.microsoft.com/en-us/dotnet/aspire/fundamentals/app-host-overview?tabs=docker#service-endpoint-environment-variable-format

[mip1983]

As David linked to, I'd noticed the aspire referenced projects appear in config, so I have a static helper class along the lines of:

 public static class ServiceUrlHelper 
 {
       public static string GetAppUrl(IConfiguration config, string appName) 
       {
               string? serviceDiscoveryUrl = configuration[$"services:{appName.ToLowerInvariant()}:https:0"];
               return serviceDiscoveryUrl;
       }
 }

e.g.

     var identityUrl = ServiceUrlHelper.GetAppUrl(config, ApplicationNames.Identity);

(Looking at it now, would probably be better as an extension method to IConfiguration)

Mine's a little more complex than this as I follow a predictable pattern to my app names/url's, so it'll resolve projects where the name ends with '-api' to the aspire config url as above, but for publicly accessible web apps it's always {appName}{-environment suffix if not prod}.{domain} so I'll resolve these by pattern.

I use 'PublishAsAzureContainerApp' and 'ConfigureCustomDomain' to configure domains now, but it doesn't look like those domains get registered as endpoints in the config at the moment, just the 'containerapps.io' internal ones.

[mmacneil]

Ah, got it now. Thanks so much gentlemen! 🙏🙏

[mmacneil]

For future travellers, here's a small method to extract the endpoint from the env variable. Extend with appropriate error handling for your production code.

public static class ServiceDiscoveryUtilities
{
    public static string? GetServiceEndpoint(string serviceName, string endpointName, int index = 0) =>
      Environment.GetEnvironmentVariable($"services__{serviceName}__{endpointName}__{index}");
}

[AldeRoberge]

Thanks for the help, I was also wondering the same. Is this really the actual way to do this? It feels... hacky.

[mmacneil]

Yeah, a bit crude for sure, but I don't believe there's any better built-in mechanism atm...at the end of the day, it's just reading environment variables so you could certainly build something sturdier on top of this to suit your needs.