Feature Request: Allow Custom Puppeteer Launch Arguments For AWS Lambda Runtime

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In this article, we will explore the feature request to allow custom Puppeteer launch arguments for AWS Lambda runtime when using marp-cli. Marp CLI is a powerful tool for creating beautiful slide decks from Markdown, but its default configuration doesn't always play nicely with serverless environments like AWS Lambda. This article delves into the problem, current behavior, expected behavior, and proposed solutions to make marp-cli more adaptable to such environments. By understanding the nuances of AWS Lambda and Puppeteer, we can enhance marp-cli to seamlessly generate PDFs and images in serverless architectures. This feature enhancement not only broadens the usability of marp-cli but also aligns it with modern cloud-native development practices. The ability to customize Puppeteer launch arguments is crucial for overcoming the limitations imposed by sandboxed environments like AWS Lambda, ensuring that marp-cli remains a versatile tool for various deployment scenarios. Let’s delve deeper into the core issue and the proposed solutions to make marp-cli a more robust tool for serverless environments.

Problem Description

The core of the issue lies in the incompatibility of default Puppeteer launch arguments with the AWS Lambda runtime environment. Marp-cli, by default, uses a predefined set of Puppeteer launch arguments that are generally suitable for standard environments. However, these hardcoded arguments do not account for the specific requirements and limitations of serverless environments like AWS Lambda. When running within AWS Lambda, the PDF and image generation processes often fail because the default arguments are not designed to operate within Lambda's sandboxed environment. AWS Lambda imposes certain restrictions and requires specific Chrome/Chromium flags to ensure proper execution. The absence of a mechanism to customize or override these browser launch arguments severely restricts the utility of marp-cli in such contexts. This limitation means that users who wish to leverage marp-cli in serverless workflows are currently unable to do so without significant workarounds or modifications. The ability to specify custom arguments would not only resolve this issue but also provide greater flexibility for users deploying marp-cli in diverse environments with varying constraints. Addressing this problem is essential for making marp-cli a truly versatile tool capable of meeting the demands of modern cloud-based applications.

Current Behavior

Currently, the default Puppeteer launch arguments within marp-cli are the primary cause of failure when running in an AWS Lambda environment. The existing configuration does not account for the sandboxed nature of Lambda, which requires specific settings for Chrome/Chromium to function correctly. As a result, when marp-cli attempts to generate PDFs or images, the process often fails due to these incompatible settings. There is no built-in way to modify or override these browser launch arguments, leaving users with limited options to adapt the tool to their specific needs. This rigid behavior prevents marp-cli from being effectively used in serverless architectures without significant manual intervention. The inability to customize these arguments means that users are unable to leverage the scalability and cost-effectiveness of AWS Lambda for their slide generation workflows. This limitation underscores the need for a more flexible approach that allows users to tailor the Puppeteer launch arguments to suit the constraints of their deployment environment, particularly in serverless contexts like AWS Lambda. By addressing this inflexibility, marp-cli can become a more adaptable and valuable tool for a wider range of users.

Expected Behavior

The desired behavior is to enable users to customize Puppeteer launch arguments, allowing marp-cli to function seamlessly in restricted environments like AWS Lambda. This would involve providing a mechanism to pass additional or custom arguments to Puppeteer, thereby overriding or supplementing the default settings. By implementing this feature, users would gain the flexibility needed to adapt marp-cli to various deployment contexts, including serverless environments that impose specific requirements. This enhanced customization would ensure that marp-cli can be used effectively in AWS Lambda and other similar environments, where specific Chrome/Chromium flags are necessary for proper execution. The ability to tailor the launch arguments would also cater to users with unique needs or constraints, such as those related to security, performance, or resource utilization. Ultimately, the expected behavior is to make marp-cli a more versatile and robust tool, capable of meeting the diverse demands of modern application development and deployment scenarios. This flexibility would significantly enhance the user experience and expand the applicability of marp-cli across a broader range of use cases.

Proposed Solutions

To address the issue of customizing Puppeteer launch arguments, several solutions can be implemented. Each option offers a unique approach to providing this flexibility, and the choice may depend on factors such as ease of use, integration with existing workflows, and overall maintainability. Here are three potential solutions:

Option 1: Environment Variable

One approach is to use an environment variable to specify the desired Puppeteer arguments. This method would involve setting an environment variable, such as MARP_PUPPETEER_ARGS, with a string containing the arguments. For example:

MARP_PUPPETEER_ARGS="--no-sandbox,--disable-setuid-sandbox,--disable-dev-shm-usage" marp --pdf presentation.md

This approach is relatively straightforward to implement and allows users to easily configure the arguments without modifying the command-line invocation. Environment variables are a common way to configure applications in various environments, including AWS Lambda, making this a familiar and convenient option for many users. This method also allows for dynamic configuration, where the arguments can be set based on the environment in which the application is running. For instance, different arguments could be used in development versus production environments. The use of environment variables provides a clean separation of configuration from code, which is a best practice for application development and deployment. This approach enhances the portability and maintainability of marp-cli, making it easier to manage and deploy in diverse environments. By leveraging environment variables, users can seamlessly integrate marp-cli into their existing workflows and infrastructure.

Option 2: CLI Flag

Another option is to introduce a command-line interface (CLI) flag specifically for passing Puppeteer arguments. This would involve adding a new flag, such as --puppeteer-args, that accepts a string containing the arguments. For example:

marp --pdf --puppeteer-args="--no-sandbox,--disable-setuid-sandbox" presentation.md

This approach provides a direct and explicit way to specify the arguments when invoking marp-cli from the command line. CLI flags are a standard way to configure command-line tools, making this a natural and intuitive option for many users. This method also allows for ad-hoc configuration, where the arguments can be specified on a per-invocation basis, providing flexibility for different use cases. The use of a dedicated CLI flag enhances the discoverability of this feature, making it easier for users to find and use. This approach also allows for better validation of the arguments, as the CLI can enforce certain rules or constraints on the input. For instance, the CLI could check for invalid or conflicting arguments, providing helpful error messages to the user. By incorporating a CLI flag, marp-cli can offer a user-friendly and robust way to customize Puppeteer launch arguments, enhancing its usability and versatility.

Option 3: Configuration File

A third option is to allow users to specify the Puppeteer arguments in a configuration file. This would involve defining a section in the configuration file where the arguments can be listed. For example:

{
  "puppeteer": {
    "args": ["--no-sandbox", "--disable-setuid-sandbox", "--disable-dev-shm-usage"]
  }
}

This approach provides a structured and organized way to manage the arguments, particularly when there are many or complex settings. Configuration files are a common way to configure applications, making this a familiar and convenient option for many users. This method also allows for version control of the configuration, making it easier to track changes and revert to previous settings. The use of a dedicated configuration file enhances the readability and maintainability of the settings, particularly when the arguments are extensive. This approach also allows for hierarchical configuration, where different settings can be applied based on the environment or context. For instance, different arguments could be used in development versus production environments, or for different types of presentations. By leveraging a configuration file, marp-cli can offer a flexible and robust way to customize Puppeteer launch arguments, enhancing its usability and adaptability.

AWS Lambda Requirements

When running marp-cli in AWS Lambda, certain Puppeteer arguments are typically required to ensure proper execution. These arguments are necessary due to the sandboxed environment of Lambda, which imposes restrictions on the processes that can be run. The following arguments are commonly needed:

{
  args: [
    '--no-sandbox',
    '--disable-setuid-sandbox',
    '--disable-dev-shm-usage',
    '--disable-background-timer-throttling',
    '--disable-backgrounding-occluded-windows',
    '--disable-renderer-backgrounding',
    '--single-process' // Sometimes needed depending on Lambda configuration
  ]
}
  • --no-sandbox: This argument disables the sandbox, which is necessary because Lambda's environment does not support the sandboxing features of Chrome/Chromium.
  • --disable-setuid-sandbox: This argument disables the setuid sandbox, which is another sandboxing mechanism that is not compatible with Lambda.
  • --disable-dev-shm-usage: This argument prevents Chrome/Chromium from using /dev/shm, which is a shared memory file system that is not available in Lambda's environment.
  • --disable-background-timer-throttling: This argument prevents Chrome/Chromium from throttling timers in background pages, which can improve performance.
  • --disable-backgrounding-occluded-windows: This argument prevents Chrome/Chromium from backgrounding occluded windows, which can also improve performance.
  • --disable-renderer-backgrounding: This argument prevents Chrome/Chromium from backgrounding renderers, which can further improve performance.
  • --single-process: This argument forces Chrome/Chromium to run in a single process, which can be necessary depending on the Lambda configuration.

These arguments are crucial for ensuring that marp-cli can generate PDFs and images reliably in AWS Lambda. Without these arguments, the process may fail due to various issues related to sandboxing and resource limitations. By providing a way to specify these arguments, marp-cli can be seamlessly integrated into serverless workflows, allowing users to leverage the scalability and cost-effectiveness of AWS Lambda.

In conclusion, the ability to customize Puppeteer launch arguments is essential for making marp-cli compatible with AWS Lambda and other restricted environments. The proposed solutions, including the use of environment variables, CLI flags, and configuration files, offer various ways to implement this feature. Each option provides a unique approach to providing this flexibility, and the choice may depend on factors such as ease of use, integration with existing workflows, and overall maintainability. The arguments listed under AWS Lambda Requirements are crucial for ensuring that marp-cli can generate PDFs and images reliably in AWS Lambda, and providing a way to specify these arguments allows marp-cli to be seamlessly integrated into serverless workflows. By addressing this feature request, marp-cli can become a more versatile and robust tool, capable of meeting the diverse demands of modern application development and deployment scenarios. This enhancement not only broadens the usability of marp-cli but also aligns it with modern cloud-native development practices. The ability to customize Puppeteer launch arguments is crucial for overcoming the limitations imposed by sandboxed environments like AWS Lambda, ensuring that marp-cli remains a valuable tool for various deployment scenarios. Ultimately, this feature enhancement will improve the user experience and expand the applicability of marp-cli across a broader range of use cases.