---

name: windmill-workflows description: | Windmill workflow engine deployment and scripting. Use when: (1) Setting up Windmill self-hosted with Docker Compose (2) Building custom worker images with PDF/image processing tools (3) Writing scripts for PDF text extraction, manipulation, or conversion (4) Writing scripts for image processing with libvips (5) Configuring workers, scaling, and resource limits (6) Troubleshooting job execution or worker issues (7) Integrating Windmill with Caddy reverse proxy

Windmill Workflow Engine

Windmill is an open-source workflow engine for building internal tools with TypeScript, Python, Go, Bash, and more. This skill focuses on self-hosting and custom worker images for PDF/image processing.

Quick Reference

Architecture

CopyCaddy → Server (port 8000) → PostgreSQL
              ↓
         Workers (N replicas) → Job Containers
              ↓
            LSP (port 3001)

• Server: API + frontend
• Workers: Execute jobs, spawn Docker containers
• LSP: Editor intellisense
• PostgreSQL: State and job queue

Custom Worker with PDF/Image Tools

Build a worker with pdfcpu, Poppler, and libvips (~150MB overhead):

CopyFROM ghcr.io/windmill-labs/windmill:main

USER root

RUN apt-get update && apt-get install -y --no-install-recommends \
    poppler-utils \
    libvips-tools \
    && rm -rf /var/lib/apt/lists/*

# Add pdfcpu
RUN curl -fsSL "https://github.com/pdfcpu/pdfcpu/releases/download/v0.11.1/pdfcpu_0.11.1_Linux_x86_64.tar.xz" \
    | tar -xJf - -C /usr/local/bin --strip-components=1

Included Tools

Common Scripts

Extract text from PDF

Copyimport { $ } from "bun";

export async function main(pdfPath: string): Promise<string> {
  return await $`pdftotext -layout ${pdfPath} -`.text();
}

Convert PDF to images

Copyimport { $ } from "bun";

export async function main(pdfPath: string): Promise<string[]> {
  const outDir = `/tmp/pdf_${Date.now()}`;
  await $`mkdir -p ${outDir}`;
  await $`pdftoppm -png -r 300 ${pdfPath} ${outDir}/page`;
  return (await $`ls ${outDir}/*.png`.text()).trim().split('\n');
}

Resize image (fast, memory-efficient)

Copyimport { $ } from "bun";

export async function main(imagePath: string, width: number): Promise<string> {
  const output = `/tmp/resized_${Date.now()}.jpg`;
  await $`vipsthumbnail ${imagePath} -s ${width} -o ${output}[Q=85,strip]`;
  return output;
}

Merge PDFs

Copyimport { $ } from "bun";

export async function main(pdfs: string[]): Promise<string> {
  const output = `/tmp/merged_${Date.now()}.pdf`;
  await $`pdfunite ${pdfs.join(' ')} ${output}`;
  return output;
}

libvips vs ImageMagick

libvips is chosen for memory-constrained environments:

• 4-8x faster than ImageMagick
• 90% less memory (~200MB vs ~3GB for large images)
• Streaming architecture (processes in chunks)

Docker Compose Example

Copywindmill-worker:
  build:
    context: ./windmill-worker
    dockerfile: Dockerfile
  image: windmill-worker-custom:latest
  environment:
    - DATABASE_URL=${DATABASE_URL}
    - MODE=worker
    - WORKER_GROUP=default
  volumes:
    - /var/run/docker.sock:/var/run/docker.sock:ro
  mem_limit: 1.5g
  cpus: 1.0
  deploy:
    replicas: 2

Resource Guidelines

Scaling rule: 1 worker per 1 vCPU and 1-2 GB RAM

Reference Files

Official Documentation

Troubleshooting Quick Guide