ASP.NET Core API in Docker on Linux

Question

I have created a ASP.NET Core Web API app with Docker enabled just using the auto generated boilerplate code. Running on Docker on my Windows dev machine works just fine. But when I deploy the app to Docker running on Ubuntu, I'm not able to connect to the API. Doing a Docker ps shows that it is listening on port 8098 on the host. It is connected to the docker_default, just as my other containers which works. The port mapping, using docker -ps for the container is

 0.0.0.0:8098->8080/tcp, :::8098->8080/tcp

Looking at the container logs, it listens to the 8080-port in the container:

  Info: Microsoft.Hosting.Lifetime[14]
      Now listening on: http://[::]:8080

But when trying to connect to port 8098 I just get a 404. As far as I can tell, everything looks like it should, but it does just not work. Any suggestions on what to try next?

Hans Kilian · Accepted Answer · 2025-04-05 08:21:58Z

0

404 can only come from the service, so you are able to connect successfully. I'll take a guess that you're trying to access the Swagger pages. Swagger is only available when the application runs in development mode (see Program.cs for the if statement that causes this). The default environment for a container is not development.

To tell your application that you're running in development mode, add -e ASPNETCORE_ENVIRONMENT=Development as an option to your docker run command. Remember to place the option before the image name in the command. Something like this

docker run -p 8098:8080 -e ASPNETCORE_ENVIRONMENT=Development -d myimage

Then Swagger will be available.

If that doesn't help, then please edit your question and add

the command you use to run your container
the URL you're trying to access

Without setting the environment variable, you should still be able to access the actual API on http://localhost:8098/weatherforecast. It's only Swagger that's disabled.

All this, ofc, assumes that my guess that you're trying to access Swagger is correct :)

edited Apr 5 at 8:21

answered Apr 5 at 8:07

Hans Kilian

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1 Comment

Jonas Samuelsson Apr 5 at 13:03

Thanks Hans! That was the issue! Now I feel rather stupid... :)

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