as i learn docker, and with my professional life working primarily in the microsoft ecosystem, i have read many blogs, articles, and tutorials. these have been educational, yet I continue to run into issues and nuances as i work to move a dotnet core aspnet app into a container. i am documenting these here as i run into them.

GuidMaker is a simple dotnet core aspnet app that generates a GUID and shows which hostname generated it. it was inspired by Alex Ellis’ guid generator in node.js. this is what I am moving into a container.

initial move, needlessly exposing ports, https woes

when creating a Dockerfile i was adding EXPOSE lines like this indicated. doing this did not cause any errors, however, after reviewing the dotnet-docker repo and the ASP.NET Core Docker Sample, i noticed the sample does not use EXPOSE, and so i removed these from the GuidMaker Dockerfile.

after running docker build, i am now able to run GuidMaker with a simple port map by:

docker run --name guidmaker --rm -it -p 5001:443 legobuff/guidmaker

yet it is not responding when navigating to https://localhost:5001/api/guid, looking at the container output i see…

Hosting environment: Production
Content root path: /
Now listening on: http://[::]:80
Application started. Press Ctrl+C to shut down.

which shows it listening to http, and seeing as i do not have a port mapping for that, makes sense. so trying again with with…

docker run --name guidmaker --rm -it -p 5000:80 legobuff/guidmaker

now it works with http, but the container output shows…

warn: Microsoft.AspNetCore.HttpsPolicy.HttpsRedirectionMiddleware[3]
      Failed to determine the https port for redirect.

again, this time mapping an additional port…

docker run --name guidmaker --rm -it -p 5000:80 -p 5001:443 legobuff/guidmaker

no dice. if i was thinking, i would have known that would not work as that it telling docker to map a local port to 443 and not configuring aspnet. i also did not pay close attention to the aspnet page above. after re-reading it, i noticed the “See Hosting ASP.NET Core Images with Docker over HTTPS to use HTTPS with this image” line. that link explains how to run the container configured for https. after following the steps outlined, i am able to run via…

docker run -it -p 5001:443 \
   -e ASPNETCORE_URLS="https://+443" \
   -e ASPNETCORE_Kestrel__Certificates__Default__Password="crypticpassword" \
   -e ASPNETCORE_Kestrel__Certificates__Default__Path=/https/GuidMaker.pfx \
   -v ${HOME}/.aspnet/https:/https/ \
   --name guidmaker \

and now https://localhost:5001/api/guid works. at this point i have a working image. continued here