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Nim on Miren

Nim isn't auto-detected, so you deploy it with a Dockerfile.miren that compiles a native binary and runs it on a minimal image. This guide uses the Jester web framework.

Let your agent do this

Ask your AI coding agent to "set up this Nim 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 Nim, 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 bind 0.0.0.0. With Jester:

import jester
import std/[os, strutils]

let appPort = parseInt(getEnv("PORT", "8080"))

settings:
  port = Port(appPort)
  bindAddr = "0.0.0.0"

routes:
  get "/":
    resp "Hello from Nim on Miren!\n"

A minimal .nimble file declares the dependency and binary:

version       = "0.1.0"
author        = "you"
description   = "nim on miren"
license       = "MIT"
srcDir        = "."
bin           = @["app"]

requires "nim >= 2.0.0"
requires "jester >= 0.6.0"

The Dockerfile​

Create Dockerfile.miren in your project root:

# ----- Build stage -----
FROM nimlang/nim:2.0.8 AS builder
WORKDIR /app
COPY . .
RUN nimble install -dy && nim c -d:release --opt:speed --mm:refc -o:app app.nim

# ----- Runtime stage -----
FROM debian:12-slim
RUN apt-get update -y && apt-get install -y libpcre3 openssl ca-certificates \
    && apt-get clean && rm -rf /var/lib/apt/lists/*
COPY --from=builder /app/app /usr/local/bin/app
EXPOSE 8080
CMD ["app"]
Compile Jester with --mm:refc

Jester runs on httpbeast, which spawns worker threads. Built with Nim 2.0's default ORC memory manager, the app segfaults on startup (SIGSEGV: Illegal storage access, right after "Starting N threads"). Compiling with --mm:refc (the older reference-counting GC) fixes it. This guide also uses a glibc base (debian, via the non-Alpine nimlang/nim image) and installs libpcre3 for Jester's routing.

.dockerignore​

.git
app

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 = "nim-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 getEnv("KEY"):

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

You can also declare variables in .miren/app.toml:

[[env]]
key = "DATABASE_URL"
value = ""
required = true
sensitive = true

See App Configuration — Environment Variables.

Agent quick reference​

  • Detection: none — requires Dockerfile.miren (native binary)
  • Build: nimble install -dy && nim c -d:release --mm:refc -o:app app.nim
  • --mm:refc required: Jester/httpbeast segfaults on startup with Nim 2.0's default ORC GC
  • Runtime libs: libpcre3 openssl on debian-slim (glibc base)
  • Service is required: define a Procfile (web: /usr/local/bin/app) — the image CMD is not used
  • Port: getEnv("PORT", "8080"); Jester settings: bindAddr = "0.0.0.0"
  • Env vars: miren env set -e/-s; read with getEnv

Next steps​