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Closing the Nix Gap: From Environments to Packaged Applications for Rust

Aug 22, 2025

Domen Kožar

Should I use crate2nix, cargo2nix, or naersk for packaging my Rust application?

— (@jvmncs) January 21, 2025

This tweet shows a common problem in Nix: “Should I use crate2nix, cargo2nix, or naersk for packaging my Rust application?”

devenv solved this for development environments differently: instead of making developers package everything with Nix, we provide tools through a simple languages.rust.enable. You get cargo, rustc, and rust-analyzer in your shell without understanding Nix packaging.

But when you’re ready to deploy, you face the same problem: which lang2nix tool should you use? Developers don’t want to compare crate2nix vs cargo2nix vs naersk vs crane—they want a tested solution that works.

devenv now provides languages.rust.import, which packages Rust applications using crate2nix. We evaluated the available tools and chose crate2nix, so you don’t have to.

We’ve done this before. In PR #1500, we replaced fenix with rust-overlay for Rust toolchains because rust-overlay was better maintained. Users didn’t need to change anything—devenv handled the transition while keeping the same languages.rust.enable = true interface.

One Interface for All Languages

The typical workflow:

1. Development: Enable the language (languages.rust.enable = true) to get tools like cargo, rustc, and rust-analyzer.
2. Packaging: When ready to deploy, use languages.rust.import to package with Nix.

The same pattern works for all languages:

{ config, ... }: {
  # https://devenv.sh/languages
  languages = {
    rust.enable = true;
    python.enable = true;
    go.enable = true;
  };

  # https://devenv.sh/outputs
  outputs = {
    rust-app = config.languages.rust.import ./rust-app {};
    python-app = config.languages.python.import ./python-app {};
    go-app = config.languages.go.import ./go-app {};
  };
}

Starting with Rust

languages.rust.import automatically generates Nix expressions from Cargo.toml and Cargo.lock.

Add the crate2nix input:

$ devenv inputs add crate2nix github:nix-community/crate2nix --follows nixpkgs

Import your Rust application:

{ config, ... }:
let
  # ./app is the directory containing your Rust project's Cargo.toml
  myapp = config.languages.rust.import ./app {};
in
{
  # Provide developer environment
  languages.rust.enable = true;

  # Expose our application inside the environment
  packages = [ myapp ];

  # https://devenv.sh/outputs
  outputs = {
    inherit myapp;
  };
}

Build your application:

$ devenv build outputs.myapp

Other Languages

This API extends to other languages, each using the best packaging tool:

We’ve also started using uv2nix to provide a similar interface for Python in PR #2115.

That’s it

For feedback, join our Discord community.

Domen

devenv devlog: Processes are now tasks

Jul 25, 2025

Domen Kožar

Building on the task runner, devenv now exposes all processes as tasks named devenv:processes:<name>.

Now you can run tasks before or after a process runs - addressing a frequently requested feature for orchestrating the startup sequence.

Usage

Execute setup tasks before the process starts

devenv.nix

{
  processes.backend = {
    exec = "cargo run --release";
  };

  tasks."db:migrate" = {
    exec = "diesel migration run";
    before = [ "devenv:processes:backend" ];
  };
}

When you run devenv up or the individual process task, migrations run first.

Run cleanup after the process stops

devenv.nix

{
  processes.app = {
    exec = "node server.js";
  };

  tasks."app:cleanup" = {
    exec = ''
      rm -f ./server.pid
      rm -rf ./tmp/*
    '';
    after = [ "devenv:processes:app" ];
  };
}

Implementation

Under the hood, process-compose now runs processes through devenv-tasks run --mode all devenv:processes:<name> instead of executing them directly. This preserves all existing process functionality while adding task capabilities.

The --mode all flag ensures that both before and after tasks are executed, maintaining the expected lifecycle behavior.

What’s next?

Future work on process dependencies (#2037) will also address native health check support (process-compose#371), eliminating the need for manual polling scripts.

Domen

devenv 1.8: Progress TUI, SecretSpec Integration, Listing Tasks, and Smaller Containers

Jul 22, 2025

Domen Kožar

devenv 1.8 fixes a couple of annoying regressions since the 1.7 release, but also includes several new features:

• Progress TUI with async core
• SecretSpec integration for declarative secrets management
• Task improvements with task listing
• CLI improvements with package options support
• Smaller containers with 67% smaller images

Progress TUI

We’ve rewritten our tracing integration to improve reporting on what devenv is doing.

More importantly, devenv is now fully asynchronous under the hood, enabling parallel execution of operations. This means faster performance in scenarios where multiple independent tasks can run simultaneously.

The new progress interface provides real-time feedback on what devenv is doing:

We’re continuing to improve visibility into Nix operations to give you even better insights into the build process.

SecretSpec Integration

We’ve integrated SecretSpec, a new standard for declarative secrets management that separates secret declaration from provisioning.

This allows teams to define what secrets applications need while letting each developer, CI system, and production environment provide them from their preferred secure provider.

Learn more in Announcing SecretSpec Declarative Secrets Management.

Task improvements

Listing tasks

The devenv tasks list command now groups tasks by namespace, providing a cleaner and more organized view:

$ devenv tasks list
backend:
  └── lint (has status check)
      └── test
          └── build (watches: src/backend/**/*.py)
deploy:
  └── production
docs:
  └── generate (watches: docs/**/*.md)
      └── publish
frontend:
  └── lint
      └── test (has status check)
          └── build

Running multi-level tasks

You can now run tasks at any level in the hierarchy. By default, tasks run in single mode (only the specified task):

# Run only frontend:build (default single mode)
$ devenv tasks run frontend:build
Running tasks     frontend:build
Succeeded         frontend:build                           5ms
1 Succeeded                         5.75ms

# Run frontend:build with all its dependencies (before mode)
$ devenv tasks run frontend:build --mode before
Running tasks     frontend:build
Succeeded         frontend:lint                            4ms
Succeeded         frontend:test                            10ms
Succeeded         frontend:build                           4ms
3 Succeeded                         20.36ms

# Run frontend:build and all tasks that depend on it (after mode)
$ devenv tasks run frontend:build --mode after
Running tasks     frontend:build
Succeeded         frontend:build                           5ms
Succeeded         deploy:production                        5ms
2 Succeeded                         11.44ms

CLI improvements

Package options support

The CLI now supports specifying single packages via the --option flag (#1988). This allows for more flexible package configuration directly from the command line:

$ devenv shell --option "languages.java.jdk.package:pkg" "graalvm-oracle"

Container optimizations

The CI container ghcr.io/cachix/devenv/devenv:v1.8 has been reduced (uncompressed) from 1,278 MB in v1.7 to 414 MB in v1.8—that’s a reduction of over 860 MB (67% smaller!).

This makes devenv container much faster to pull and more efficient in CI/CD pipelines.

Thank You

Join our Discord community to share your experiences and help shape devenv’s future!

Domen

Announcing SecretSpec: Declarative Secrets Management

Jul 21, 2025

Domen Kožar

We’ve supported .env integration for managing secrets, but it has several issues:

• Apps are disconnected from their secrets - applications lack a clear contract about which secrets they need
• Parsing .env is unclear - comments, multiline values, and special characters all have ambiguous behavior across different parsers
• Password manager integration is difficult - requiring manual copy-paste or template workarounds
• Vendor lock-in - applications use custom parsing logic, making it hard to switch providers
• No encryption - .env files are stored as plain text, vulnerable to accidental commits or unauthorized access

While we could recommend solutions like dotenvx to encrypt .env files or sops for general secret encryption, these bring new challenges:

Don't you feel some anxiety given we've normalized committing encrypted secrets to git repos?

— Domen Kožar (@domenkozar) July 18, 2025

• Single key management - requires distributing and managing a master key
• Trust requirements - everyone with the key can decrypt all secrets
• Rotation complexity - departing team members require key rotation and re-encrypting all secrets

Larger teams often adopt solutions like OpenBao (the open source fork of HashiCorp Vault), requiring significant infrastructure and operational overhead. Smaller teams face a gap between simple .env files and complex enterprise solutions.

What if instead of choosing one tool, we declared secrets uniformly and let each environment use its best provider?

The Hidden Problem: Conflating Three Concerns

We’ve created SecretSpec and integrated it into devenv. SecretSpec separates secret management into three distinct concerns:

• WHAT - Which secrets does your application need? (DATABASE_URL, API_KEY)
• HOW - Requirements (required vs optional, defaults, validation, environment)
• WHERE - Where are these secrets stored? (environment variables, Vault, AWS Secrets Manager)

By separating these concerns, your application declares what secrets it needs in a simple TOML file. Each developer, CI system, and production environment can provide those secrets from their preferred secure storage - without changing any application code.

One Spec, Multiple Environments, Different Providers

Imagine you commit a secretspec.toml file that declares:

# secretspec.toml - committed to your repo
[project]
name = "my-app"
revision = "1.0"

[profiles.default]
DATABASE_URL = { description = "PostgreSQL connection string", required = true }
REDIS_URL = { description = "Redis connection string", required = false }
STRIPE_API_KEY = { description = "Stripe API key", required = true }

[profiles.development]
# Inherits from default profile - only override what changes
DATABASE_URL = { default = "postgresql://localhost/myapp_dev" }
REDIS_URL = { default = "redis://localhost:6379" }
STRIPE_API_KEY = { description = "Stripe API key (test mode)" }

[profiles.production]
# Production keeps strict requirements from default profile

Now, here’s the magic:

• You (on macOS): Store it in Keychain, retrieve with secretspec --provider keyring run -- cmd args
• Your teammate (on Linux): Store it in GNOME Keyring, same command works
• That one developer: Still uses a .env file locally (we don’t judge, we’ve been there)
• CI/CD: Reads from environment variables in GitHub Actions secretspec --provider env run -- cmd args
• Production: Secrets get provisioned using AWS Secret Manager

Same specification. Different providers. Zero code changes.

Example: One Spec, Three Environments

Let’s walk through migrating from .env to SecretSpec.

Setting up secretspec for development

First, choose your default provider and profile:

$ secretspec config init
? Select your preferred provider backend:
> keyring: Uses system keychain (Recommended)
  onepassword: OnePassword password manager
  dotenv: Traditional .env files
  env: Read-only environment variables
  lastpass: LastPass password manager
? Select your default profile:
> development
  default
  none
✓ Configuration saved to ~/.config/secretspec/config.toml

Importing secrets

Create secretspec.toml from your existing .env:

$ secretspec init --from dotenv

1. Local Development with devenv (You’re on macOS)

Enable SecretSpec in devenv.yaml:

secretspec:
  enable: true

In devenv.nix:

{ pkgs, lib, config, ... }:

{
  languages.rust.enable = true;

  services.minio = {
    enable = true;
    buckets = [ config.secretspec.secrets.BUCKET_NAME ];
  };
}

Start the minio process:

$ devenv up
✓ Starting minio...

2. CI/CD (GitHub Actions)

.github/workflows/test.yml

- name: Run tests
  env:
    DATABASE_URL: {{ secrets.TEST_DATABASE_URL }}
    STRIPE_API_KEY: {{ secrets.STRIPE_TEST_KEY }}
  run: |
    secretspec run --provider env --profile production -- npm test

3. Production (Fly.io)

fly.toml

[processes]
web = "secretspec run --provider env --profile production -- npm start"

# Set secrets using fly CLI:
# fly secrets set DATABASE_URL=postgresql://... STRIPE_API_KEY=sk_live_...
# SecretSpec will read these from environment variables

Notice what didn’t change? Your secretspec.toml. Same specification, different providers, zero code changes.

Loading secrets in your application

While secretspec run provides secrets as environment variables, your application remains disconnected from knowing which secrets it requires. The Rust SDK bridges this gap by providing type-safe access to your declared secrets.

The Rust SDK provides compile-time guarantees:

// Generate typed structs from secretspec.toml
secretspec_derive::declare_secrets!("secretspec.toml");

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Load secrets using the builder pattern
    let secretspec = SecretSpec::builder()
        .with_provider("keyring")  // Can use provider name or URI like "dotenv:/path/to/.env"
        .with_profile(Profile::Production)  // Can use string or Profile enum
        .load()?;

    // Access secrets (field names are lowercased)
    println!("Database: {}", secretspec.secrets.database_url);  // DATABASE_URL → database_url
    println!("Stripe: {}", secretspec.secrets.stripe_api_key);  // STRIPE_API_KEY → stripe_api_key

    // Optional secrets are Option<String>
    if let Some(redis) = &secretspec.secrets.redis_url {
        println!("Redis: {}", redis);
    }

    // Access profile and provider information
    println!("Using profile: {}", secretspec.profile);
    println!("Using provider: {}", secretspec.provider);

    // For backwards compatibility, export as environment variables
    secretspec.secrets.set_as_env_vars();

    Ok(())
}

Add to your Cargo.toml:

[dependencies]
secretspec = "0.2.0"
secretspec_derive = "0.2.0"

The application code never specifies where to get secrets - only what it needs through the TOML file. This keeps your application logic clean and portable.

Building SDKs for Other Languages

We’d love to see more SDKs that bring this same declarative approach to Python, JavaScript, Go, and other languages.

A world of possibilities

We’re exploring features for future workflows:

• Secret rotation without shutting down the application
• Generating secrets
• Mixing providers

Final words

Let’s make secret management as declarative as package management. Let’s stop sharing .env files over Slack. Let’s build better tools for developers.

Share your thoughts on our Discord community or open an issue on GitHub. We’d love to hear how you handle secrets in your team.

Domen

devenv 1.7: CUDA Support, Enhanced Tasks, and MCP support

Jul 3, 2025

Domen Kožar

devenv 1.7 brings several practical improvements:

• CUDA support that works across platforms
• MCP support that understands devenv configurations
• Tasks that only run when their inputs change
• Groundwork for Snix, Rust-based Nix implementation

Progress on Snix Support

We’ve started work on supporting multiple Nix implementations in devenv. The codebase now includes a backend abstraction layer that will allow users to choose between different Nix implementations.

This architectural change paves the way for integrating Snix (our development fork). While the Snix backend isn’t functional yet, the groundwork is in place for building out this Rust-based reimplementation to the C++ Nix implementation. See PR #1950 for implementation details.

Platform-Specific Configuration

Here’s how to enable CUDA support only on Linux systems while keeping your environment working smoothly on macOS:

• CUDA-enabled packages are built with GPU support on Linux
• macOS developers can still work on the same project without CUDA
• The correct CUDA capabilities are set for your target GPUs

devenv.yaml

nixpkgs:
  config:
    allowUnfree: true
    x86_64-linux:
      cudaSupport: true
      cudaCapabilities: ["7.5", "8.6", "8.9"]

Tasks Enhancements

Tasks now skip execution when their input files haven’t changed, using the new execIfModified option:

{
  tasks = {
    "frontend:build" = {
      exec = "npm run build";
      execIfModified = [ "src/**/*.tsx" "src/**/*.css" "package.json" ];
    };

    "backend:compile" = {
      exec = "cargo build --release";
      execIfModified = [ "src/**/*.rs" "Cargo.toml" "Cargo.lock" ];
    };
  };
}

This dramatically speeds up incremental builds by skipping unnecessary work.

Namespace-Based Task Execution

Run all tasks within a namespace using prefix matching:

# Run all frontend tasks
$ devenv tasks run frontend

Model Context Protocol (MCP) Support

devenv now includes a built-in MCP server that enables AI assistants like Claude to better understand and generate devenv configurations:

# Start the MCP server
$ devenv mcp

AI assistants can now:

• Search for packages and their options
• Understand devenv’s configuration format
• Generate valid configurations based on your requirements

Quality of Life Improvements

• Shell Integration: Your shell aliases and functions now work correctly
• Clean Mode: Fixed shell corruption when using --clean
• Error Messages: More helpful error messages when commands fail
• State Handling: Automatically recovers from corrupted cache files
• Direnv Integration: Fewer unnecessary environment reloads

Upcoming 1.8 Release

Standardized Language Tooling Configuration

All language modules will support the same configuration pattern (PR #1974):

{
  languages.rust.dev = {
    lsp.enable = false;
    debugger.enable = false;
    linter.enable = false;
    formatter.enable = false;
  };
}

Rust Import Functionality

Import Rust projects and their dependencies as Nix packages with the new languages.rust.import configuration (PR #1946):

{
  languages.rust.enable = true;
  languages.rust.import = {
    mypackage = {
      root = ./.;
    };
  };
  packages = languages.rust.import.mypackage.packages;
}

That allows us to bridge the gap between developer environments and fully packaged Rust applications using Nix.

Async Core

Operations that can run in parallel will (PR #1970).

Getting Started

Join our Discord community to share your experiences and help shape devenv’s future.

We’re particularly interested in feedback on the standardized language tooling configuration coming in 1.8 - let us know if this approach works for your use cases!

Domen

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