Use new Redis instrumentation in an ASP.NET Core app

APM Agent version

1.8.0

Environment

.NET Framework/Core name and version (e.g. .NET 4.6.1, NET Core 3.1.100) : .NET 5.0

Application Target Framework(s) (e.g. net461, netcoreapp3.1): net5.0

Describe the bug

It seems to be impossible to configure the Redis instrumentation inside of an ASP.NET Core app while registering the ConnectionMultiplexer into the DI services collection in the Startup.ConfigureServices method. Calling UseElasticApm on the ConnectionMultiplexer triggers an access to the Agent.Instance singleton therefore configuring the instance and locking it. When you later call app.UseElasticApm in the Startup.Configure method you get an Elastic.Apm.Agent.InstanceAlreadyCreatedException with a message saying The singleton APM agent has already been instantiated and can no longer be configured.

Honestly, I have to say that working with the Elastic APM agent configuration has been a pretty poor experience as I have run into several roadblocks along the way.

[russcam]

Thanks for your time earlier @ejsmith.

I’ve opened https://github.com/elastic/apm-agent-dotnet/pull/1192 to lazily access the agent in the redis integration when accessed through the Agent.Instance static property.

An approach that might be of interest to other folks that do need to use Redis early in startup, and before the agent is initialized, it would be possible right now to register the redis integration after initialization of the agent in app configure. For example, in ConfigureServices

services.AddSingleton(_ => {
	const string redisConnection = @"localhost,abortConnect=false";
	var redisConnectionMultiplexer = ConnectionMultiplexer.Connect(redisConnection);
	return redisConnectionMultiplexer;
});

Then, in Configure

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
   // Some call to redis happens **before** the agent is initialized

    // agent initialized here
    app.UseAllElasticApm(Configuration);

    var muxer = app.ApplicationServices.GetService<ConnectionMultiplexer>();
    // register redis integration
    muxer.UseElasticApm();

    // other app setup
}

It does mean that those initial redis calls won’t be traced, but would avoid the Elastic.Apm.Agent.InstanceAlreadyCreatedException.

As part of https://github.com/elastic/apm-agent-dotnet/pull/1161, Elastic.Apm.Agent.InstanceAlreadyCreatedException is removed and there will be an error log instead.

[ejsmith]

Thanks @russcam for getting on a Zoom call with me and helping me figure out this issue. For anyone else looking at this, Russ is going to make the agent access in the ElasticApmProfiler lazy and he helped me find where my app was aggressively loading a dependency and causing the agent to be configured before the other app.UseElasticApm call was made.