Empirical Study of the Docker Smells Impact on the Image Size

Docker, a widely adopted tool for packaging and deploying applications leverages Dockerfiles to build images. However, creating an optimal Dockerfile can be challenging, often leading to "Docker smells" or deviations from best practices. This paper presents a study of the impact of 14 Docker smells on the size of Docker images. To assess the size impact of Docker smells, we identified and repaired 16 145 Docker smells from 11 313 open-source Dockerfiles. We observe that the smells result in an average increase of 48.06 MB (4.6 %) per smelly image. Depending on the smell type, the size increase can be up to 10 %, and for some specific cases, the smells can represent 89 % of the image size. Interestingly, the most impactful smells are related to package managers which are commonly encountered and are relatively easy to fix. To collect the perspective of the developers regarding the size impact of the Docker smells, we submitted 34 pull requests that repair the smells and we reported their impact on the Docker image to the developers. 26/34 (76.5 %) of the pull requests have been merged and they contribute to a saving of 3.46 GB (16.4 %). The developer's comments demonstrate a positive interest in addressing those Docker smells even when the pull requests have been rejected.