On the prevalence, co-occurrence, and impact of infrastructure-as-code smells

In modern software systems, Infrastructure-as-Code (IaC) tools play a pivotal role in automating the management of various infrastructure resources such as networks, databases, and services. This automation is done through code-based specification files, commonly known as IaC files. Similarly to other code files, IaC files can suffer from violations of established implementation and design standards, i.e., IaC smells. Although prior research has studied various aspects of traditional smells in non-IaC artifacts, there is little knowledge of how IaC smells are prevalent, co-occurring, and impacting the change and defect proneness of IaC code. To fill this gap, we conduct an empirical study encompassing 82 Puppet-based open-source projects. Our investigation focused on 12 types of IaC smells in both implementation and design levels. Our findings reveal that IaC smells do not manifest uniformly, as IaC smells that are particularly associated with modularity issues, exhibit high prevalence rates across projects. Additionally, we found that 74% of IaC files are smelly and over 52% of the smelly IaC files have at least two co-occurring IaC smells. Furthermore, our findings highlight that, on average, smelly IaC files are modified nearly 3.8 times, in terms of number of commits, more frequently than non-smelly IaC files. Furthermore, smelly IaC files are found to be 3.1 times more prone to larger code changes, in terms of code churn, than non-smelly IaC files. Additionally, we found that smelly IaC files are 3.3 times more prone to the introduction of defects that are likely to persist in 1.65 more commits before being fixed than non-smelly IaC files. These findings advocate developers to be more aware of IaC smells in their projects and consider their correction