Gotenberg

A stateless API for converting Markdown files, HTML files and Office documents to PDF

At TheCodingMachine, we build a lot of web applications (intranets, extranets and so on) which require to generate PDF from various sources. Each time, we end up using some well known libraries like wkhtmltopdf or unoconv and kind of losing time by reimplementing a solution from a project to another project. Meh.

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Menu

• Usage
• Security
• Scalability
• Custom implementation

Usage

Let's say you're starting the API using this simple command:

$ docker run --rm -p 3000:3000 thecodingmachine/gotenberg:1.0.0

The API is now available on your host under http://127.0.0.1:3000.

It accepts POST requests with a multipart/form-data Content-Type. Your form data should provide one or more files to convert. It currently accepts the following:

• Markdown files
• HTML files
• Office documents (.docx, .doc, .odt, .pptx, .ppt, .odp and so on)
• PDF files (if more than one file to convert)

Heads up: the API relies on the file extension to determine which library to use for conversion.

There are two use cases:

• If you send one file, it will convert it and return the resulting PDF.
• If many files, it will convert them to PDF, merge the resulting PDFs into a single PDF and return it.

Security

The API does not provide any authentication mechanisms. Make sure to not put it on a public facing port and your client(s) should always controls what's is sent to the API.

Scalability

Some libraries like unoconv cannot perform concurrent conversions. That's why the API does only one conversion at a time. If your API is under heavy load, a request will take time to be processed.

Fortunately, you may pass through this limitation by scaling the API.

In the following example, I'll demonstrate how to do some vertical scaling (= on the same machine) with Docker Compose, but of course horizontal scaling works too!

version: '3'

services:

  # your other services

  gotenberg-proxy:
    # Traefik is a powerful HTTP reverse proxy which allows us to do some load-balancing. 
    # It provides various methods of load-balancing which are not described here.
    # More information: https://traefik.io/
    image: traefik:1.5-alpine
    command: --docker --logLevel=DEBUG
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock:ro
      
  gotenberg:
    image: gotenberg:1.0.0
    labels:
      - traefik.backend=gotenberg
      - traefik.frontend.rule=Host:gotenberg.yourdomain.com
      - traefik.port=3000

You may now launch your services using:

docker-compose up --scale gotenberg=your_number_of_instances

When requesting gotenberg.yourdomain.com with your client(s), Traefik will automatically redirect a request to a Gotenberg container according to the load-balancing strategy you have defined.

Custom implementation

The API relies on a simple YAML configuration file called gotenberg.yml. It allows you to tweak some values and even provides you a way to change the commands called for each kind of conversion.

The default configuration is located here: .ci/gotenberg.yml

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