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C++ on Miren

C++ isn't auto-detected, so you deploy it with a Dockerfile.miren that compiles your program and runs the binary. This guide uses the header-only cpp-httplib library.

Let your agent do this

Ask your AI coding agent to "set up this C++ app on Miren" after installing the Miren agent skills. It adds the Dockerfile.miren, confirms the server binds 0.0.0.0:$PORT, and deploys — using this page as its reference.

Do you need a Dockerfile?​

Yes. Miren doesn't auto-detect C++, 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 read PORT and listen on 0.0.0.0:

#include "httplib.h"
#include <cstdlib>

int main() {
    httplib::Server svr;
    svr.Get("/", [](const httplib::Request &, httplib::Response &res) {
        res.set_content("Hello from C++ on Miren!\n", "text/plain");
    });
    const char *p = std::getenv("PORT");
    int port = p ? std::atoi(p) : 8080;
    if (!svr.listen("0.0.0.0", port)) {
        return 1;  // bind/startup failed — surface it to the deploy
    }
    return 0;
}

The Dockerfile​

Create Dockerfile.miren in your project root. It fetches the single httplib.h header and compiles with pthreads:

FROM gcc:14 AS build
WORKDIR /app
RUN apt-get update -y && apt-get install -y curl && rm -rf /var/lib/apt/lists/*
COPY main.cpp .
RUN curl -sSL -o httplib.h https://raw.githubusercontent.com/yhirose/cpp-httplib/v0.18.3/httplib.h \
    && g++ -O2 -std=c++17 -pthread -o app main.cpp

FROM debian:trixie-slim
COPY --from=build /app/app /usr/local/bin/app
EXPOSE 8080
CMD ["app"]
Match the runtime to the compiler image

The gcc:14 image is built on Debian trixie (glibc 2.38, a newer libstdc++). Running the binary on an older base like debian:12-slim fails at startup with GLIBC_2.38 not found / GLIBCXX_3.4.32 not found. Use a runtime base from the same or newer Debian release (debian:trixie-slim), or statically link the C++ runtime with -static-libstdc++ -static-libgcc.

.dockerignore​

.git

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: /usr/local/bin/app

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

name = "cpp-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 std::getenv("KEY"):

miren env set -e LOG_LEVEL=info
miren env set -s DATABASE_URL

See App Configuration — Environment Variables.

Agent quick reference​

  • Detection: none — requires Dockerfile.miren
  • Build: fetch httplib.h; g++ -O2 -std=c++17 -pthread -o app main.cpp on gcc:14
  • Runtime glibc/libstdc++: use debian:trixie-slim (matches gcc:14) — older bases crash on GLIBC_2.38/GLIBCXX_3.4.32
  • Service is required: define a Procfile (web: /usr/local/bin/app) — the image CMD is not used
  • Port: std::getenv("PORT"); svr.listen("0.0.0.0", port)
  • Env vars: miren env set -e/-s; read with std::getenv

Next steps​