How to integrate Einhorn with a Go HTTP server?

Use the go-einhorn library to handle socket file descriptors from environment variables, or implement manual ACK by sending JSON messages to the command socket as described in the README. Ensure your server binds to the passed descriptors instead of creating new sockets.

Einhorn vs Gunicorn for Python apps?

Einhorn is language-agnostic and focuses on socket sharing for seamless upgrades, while Gunicorn is Python-specific with built-in HTTP worker management. Choose Einhorn for multi-protocol servers or mixed-language environments, and Gunicorn for pure Python web apps with more HTTP features.

Can Einhorn handle database connection pooling across workers?

No, Einhorn only manages sockets and processes; each worker must handle its own database connections and pooling. You'll need to implement graceful shutdown logic to avoid connection leaks during upgrades, as Einhorn sends SIGUSR2 but doesn't manage app state.

How to monitor Einhorn worker health in production?

Einhorn provides basic ACKs but no built-in metrics; use external tools to check process status via PID files or custom health endpoints. The command socket allows manual queries, but for dashboards, you'll need to integrate with systems like Prometheus or logging services.

What happens if Einhorn master process crashes?

Workers may continue running but lose management; use the -k option with the fiddle gem on Linux to gracefully kill children on exit, but this is limited and not cross-platform, so additional supervision like systemd is recommended for high availability.

How to dynamically add or remove workers with Einhorn?

Use the command socket via einhornsh to reconfigure worker counts on the fly, but it requires manual intervention. For auto-scaling, you'll need external scripts to trigger commands based on load, as Einhorn doesn't support automatic scaling out of the box.

Einhorn — Shared Socket Process Manager

What is Einhorn?

Einhorn is a language-independent shared socket manager that runs and keeps alive multiple copies of a long-lived process, such as a server. It manages shared sockets in a master process, passes them to worker processes, and supports seamless code upgrades and dynamic reconfiguration. It solves the problem of maintaining robust, restartable server processes with minimal application changes.

Target Audience

Developers and operations engineers running long-lived server processes (e.g., API workers, TCP servers) who need zero-downtime deployments, process supervision, and shared socket management across multiple languages.

Value Proposition

Einhorn provides the proven master/worker process model of servers like Unicorn, but generalized to work with any language or framework. Its minimal dependencies, simple configuration, and support for seamless upgrades make it a lightweight yet powerful alternative to language-specific process managers.

Einhorn: the language-independent shared socket manager

Use Cases

Best For

Running multiple copies of a TCP or HTTP server with shared listening sockets
Implementing zero-downtime code reloads for long-running processes
Managing worker processes in polyglot environments with mixed language services
Supervising and keeping alive critical backend services with automatic respawning
Reducing memory overhead via copy-on-write preloading for Ruby applications
Administering server processes dynamically via a command socket

Not Ideal For

Applications deployed in container orchestration systems like Kubernetes, where built-in process managers handle lifecycle and scaling automatically
Projects requiring built-in load balancing, request routing, or advanced HTTP features beyond basic socket sharing
Teams needing out-of-the-box monitoring dashboards, centralized logging, or configuration management without additional tooling
Services that must auto-scale dynamically based on real-time metrics without manual command socket intervention

Pros & Cons

Pros

Shared Socket Management

Einhorn opens server sockets in the master process and passes file descriptors to workers via environment variables, enabling zero-downtime upgrades without application-level socket handling, as detailed in the README with examples for binding addresses.

Language Agnostic Design

Compatible with arbitrary languages, requiring only minimal code to read environment variables like EINHORN_FD_0, with libraries available for Go, PHP, and Python, as noted in the Compatibility section.

Seamless Code Reloads

Supports hot upgrades by spawning new workers and gracefully shutting down old ones with SIGUSR2, allowing code updates without dropping connections, demonstrated in the 'Seamless upgrades' section.

Flexible Worker Readiness

Offers manual or timer-based ACK mechanisms, giving precise control over worker health confirmation, with Ruby helpers and socket communication options outlined in the ACKs section.

Cons

Ecosystem Fragmentation

Integration libraries for non-Ruby languages are community-maintained and vary in quality, requiring custom implementation for unsupported frameworks, as hinted in the Compatibility list without official endorsement.

Ruby-Centric Optimizations

Preloading and copy-on-write memory savings are only available for Ruby applications via the -p flag, leaving other languages with slower worker startups and higher memory overhead.

Security Reliance on Permissions

The command socket uses a line-oriented YAML protocol and depends on file system permissions for security, which the README warns could be risky if misconfigured or exposed to malicious inputs.

What is Einhorn?

Target Audience

Value Proposition

Use Cases

Best For

Running multiple copies of a TCP or HTTP server with shared listening sockets
Implementing zero-downtime code reloads for long-running processes
Managing worker processes in polyglot environments with mixed language services
Supervising and keeping alive critical backend services with automatic respawning
Reducing memory overhead via copy-on-write preloading for Ruby applications
Administering server processes dynamically via a command socket

Not Ideal For

Applications deployed in container orchestration systems like Kubernetes, where built-in process managers handle lifecycle and scaling automatically
Projects requiring built-in load balancing, request routing, or advanced HTTP features beyond basic socket sharing
Teams needing out-of-the-box monitoring dashboards, centralized logging, or configuration management without additional tooling
Services that must auto-scale dynamically based on real-time metrics without manual command socket intervention

Pros & Cons

Pros

Shared Socket Management

Language Agnostic Design

Seamless Code Reloads

Supports hot upgrades by spawning new workers and gracefully shutting down old ones with SIGUSR2, allowing code updates without dropping connections, demonstrated in the 'Seamless upgrades' section.

Flexible Worker Readiness

Offers manual or timer-based ACK mechanisms, giving precise control over worker health confirmation, with Ruby helpers and socket communication options outlined in the ACKs section.

Cons

Ecosystem Fragmentation

Ruby-Centric Optimizations

Preloading and copy-on-write memory savings are only available for Ruby applications via the -p flag, leaving other languages with slower worker startups and higher memory overhead.

Security Reliance on Permissions

The command socket uses a line-oriented YAML protocol and depends on file system permissions for security, which the README warns could be risky if misconfigured or exposed to malicious inputs.

Einhorn

What is Einhorn?

Overview

Use Cases

Best For

Not Ideal For

Pros & Cons

Pros

Cons

Frequently Asked Questions

Related Projects

Found a gem we're missing?

Einhorn

What is Einhorn?

Overview

Use Cases

Best For

Not Ideal For

Pros & Cons

Pros

Cons

Frequently Asked Questions

Related Projects

Found a gem we're missing?