CI/CD pipelines are widely used in software development, yet their environmental impact, particularly carbon and water footprints (CWF), remains largely unknown to developers, as CI service providers typically do not disclose such information. With the growing environmental impact of cloud computing, understanding the CWF of CI/CD services has become increasingly important. This work investigates the CWF of using GitHub Actions, focusing on open-source repositories where usage is free and unlimited for standard runners. We build upon a methodology from the Cloud Carbon Footprint framework and we use the largest dataset of workflow runs reported in the literature to date, comprising over 2.2 million workflow runs from more than 18,000 repositories. Our analysis reveals that the GitHub Actions ecosystem results in a substantial CWF. Our estimates for the carbon footprint in 2024 range from 150.5 MTCO2e in the most optimistic scenario to 994.9 MTCO2e in the most pessimistic scenario, while the water footprint ranges from 1,989.6 to 37,664.5 kiloliters. The most likely scenario estimates are 456.9 MTCO2e for carbon footprint and 5,738.2 kiloliters for water footprint. To provide perspective, the carbon footprint in the most likely scenario is equivalent to the carbon captured by 7,615 urban trees in a year, and the water footprint is comparable to the water consumed by an average American family over 5,053 years. We explore strategies to mitigate this impact, primarily by reducing wasted computational resources. Key recommendations include deploying runners in regions whose energy production has a low environmental impact such as France and the United Kingdom, implementing stricter deactivation policies for scheduled runs and aligning their execution with periods when the regional energy mix is more environmentally favorable, and reducing the size of repositories.

翻译：CI/CD 流水线在软件开发中被广泛使用，但其环境影响，特别是碳足迹和水足迹（CWF），对开发者而言在很大程度上仍是未知的，因为 CI 服务提供商通常不披露此类信息。随着云计算环境影响的日益增长，理解 CI/CD 服务的 CWF 变得越来越重要。本研究调查了使用 GitHub Actions 的 CWF，重点关注开源仓库，其中标准运行器的使用是免费且无限制的。我们基于云碳足迹框架的方法论，并使用了文献中迄今报道的最大规模的工作流运行数据集，包含来自超过 18,000 个仓库的 220 多万次工作流运行。我们的分析表明，GitHub Actions 生态系统产生了显著的 CWF。我们对 2024 年碳足迹的估计范围从最乐观情景下的 150.5 MTCO2e 到最悲观情景下的 994.9 MTCO2e，而水足迹范围从 1,989.6 到 37,664.5 千升。最可能情景下的估计值为碳足迹 456.9 MTCO2e 和水足迹 5,738.2 千升。为提供视角，最可能情景下的碳足迹相当于 7,615 棵城市树木一年吸收的碳量，水足迹则相当于一个美国家庭 5,053 年的用水量。我们探讨了减轻这种影响的策略，主要是通过减少浪费的计算资源。关键建议包括：在能源生产环境影响较低的地区（如法国和英国）部署运行器；对计划运行实施更严格的停用策略，并将其执行与区域能源结构更环保的时段对齐；以及减小仓库的大小。