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.NET on Miren

.NET isn't auto-detected, so you deploy ASP.NET Core apps with a Dockerfile.miren that publishes your app with the SDK image and runs it on the smaller ASP.NET runtime image.

Let your agent do this

Ask your AI coding agent to "set up this .NET app on Miren" after installing the Miren agent skills. It adds the Dockerfile.miren, points Kestrel at 0.0.0.0:$PORT, wires up environment variables, and deploys — using this page as its reference.

Do you need a Dockerfile?​

Yes. Miren doesn't auto-detect .NET, so add a Dockerfile.miren to your project root. Miren builds from it instead of guessing the stack — see Using Dockerfile.miren.

Want native support?

Miren auto-detects and builds common stacks (Python, Node, Bun, Go, Ruby, Rust) without a Dockerfile. This language isn't one of them yet — if you'd like first-class support, request it.

Bind to the injected port​

Miren injects PORT and routes traffic to it, so Kestrel must listen on 0.0.0.0 at that port. The simplest way is to pass the URL to app.Run:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", () => "Hello from .NET on Miren!\n");

var port = Environment.GetEnvironmentVariable("PORT") ?? "8080";
app.Run($"http://0.0.0.0:{port}");

Reading PORT in code (as above) is the simplest approach. ASPNETCORE_URLS also works, but Miren stores env vars literally and does not shell-expand $PORT, so you can't set it to http://0.0.0.0:$PORT in app.toml — the app would receive that literal string. Use it only from a shell entrypoint that expands PORT at runtime.

The Dockerfile​

Create Dockerfile.miren in your project root. Replace dotnet-bench.dll with your project's assembly name:

# ----- Build stage -----
FROM mcr.microsoft.com/dotnet/sdk:9.0 AS builder
WORKDIR /app
COPY . .
RUN dotnet publish -c Release -o /out

# ----- Runtime stage -----
FROM mcr.microsoft.com/dotnet/aspnet:9.0
WORKDIR /app
COPY --from=builder /out .
EXPOSE 8080
CMD ["dotnet", "dotnet-bench.dll"]

.dockerignore​

.git
bin
obj

Set up the app​

Even with a Dockerfile.miren, Miren needs at least one service defined — it doesn't use the image's CMD as the start command. Add a Procfile:

web: dotnet /app/dotnet-bench.dll

Then create .miren/app.toml naming your app and deploy from your project root:

name = "dotnet-bench"
miren deploy
Deploying without a service fails

If no service is defined, the build succeeds but the deploy stops with no services defined: please define at least one service in a Procfile or .miren/app.toml.

Environment variables​

Set variables with miren env set — -e for plain values, -s for secrets (masked in output and logs). Read them with Environment.GetEnvironmentVariable or the configuration system:

miren env set -e ASPNETCORE_ENVIRONMENT=Production
miren env set -s ConnectionStrings__Default

.NET maps __ in an env var name to nested configuration keys, so ConnectionStrings__Default becomes ConnectionStrings:Default. You can also declare variables in .miren/app.toml:

[[env]]
key = "ASPNETCORE_ENVIRONMENT"
value = "Production"

See App Configuration — Environment Variables.

Agent quick reference​

  • Detection: none — requires Dockerfile.miren
  • Build: dotnet publish -c Release -o /out on the SDK image; run on dotnet/aspnet
  • Service is required: define a Procfile (web: dotnet /app/<assembly>.dll) — the image CMD is not used
  • Port: app.Run($"http://0.0.0.0:{port}") (reading PORT in code; ASPNETCORE_URLS is not shell-expanded)
  • Env vars: miren env set -e/-s; __ maps to nested config keys
  • Database: optional [addons.miren-postgresql] injects DATABASE_URL

Next steps​