The life sciences are becoming more and more digital and nowadays data analysis methods represent a key factor of the discovery process. In the case of bioinformatics, software is widely provided by the research community. Developers favor open source approaches and many software tools are available online. It is commonly agreed that such a distributed and free creation process accelerates discoveries in the life sciences ^{1, 2} . However, this view must be nuanced, as multiple factors still hinder the discovery, integration, and maintenance of these software tools.

First, domains such as genomics, where technological innovation leads to a exponential growth of data to analyse, also generate an ever-increasing number of new software methods. However, the discovery of new interesting tools by potential users remains limited by unstructured descriptions, lack of metadata and deprecated source codes. In this context, dedicated search engines like the ELIXIR Tools and Data Services Registry ^{3, 4} (hereafter referred as the "ELIXIR registry") have emerged as a potential solution to search, find and locate available and maintained tools.

Secondly, the implementation methods of bioinformatic software are heterogeneous and their deployment requires multiple technical skills. The installation process is therefore expensive, in terms of human resources. It is worth recalling that the cost in supporting operating systems and hardware diversity can be high, the code compilation process is error prone and the required software dependencies are often conflicting with installed libraries. Consequently, the audience of a software can be limited to highly motivated and technical users or large bioinformatics facilities. The recent development of user-friendly data analysis environments like Galaxy ⁵ ease access for biologists and bio-analysts to bioinformatic tools. These software workbenches provide a generic web user interface for command line based scientific applications, but do not solve the tools’ deployment issue. Even if the task can be submitted inside a container, it is the tool designer’s responsibility to provide a readily deployable component ⁶ and the proportion of container based components in repositories such as the Galaxy Toolsheds ⁷ is currently low.

Finally, traditional academic publishing and funding processes emphasize the production of software with short-term goals, these being the publication of the method and/or results. Such an environment does not favor a software engineering-oriented approach to software development ⁸ , and this affects directly the portability and maintainability of the software products ⁹ . This in turn impacts the reproducibility of analyses, experiments or benchmarks described in published articles. However, even if various emerging initiatives are developing frameworks ^{10– 12} to enable a new kind of "executable format" of scientific publication, few journals have an innovative publishing policy that includes the long term storage of the source codes on a dedicated public web platform.

Nevertheless, today containerization brings new pragmatic solutions. Linux containers are a mature technology that has the potential to dramatically facilitate scientific software deployment and analysis reproducibility. Docker, one of the most popular container solutions ^{13, 14} , is now used in a variety of computation environments, from commercial clouds ¹⁵ to clusters with dedicated middleware ¹⁶ . It has been positively evaluated for data intensive computation, a recent study showing that the performance of bioinformatic workflows composed by medium or long running tasks are only very slightly affected by containerization ¹⁷ .

Container technology has the potential to impact audiences, developers and end-users. In the scientific field, it can effectively improve reproducibility, ease deployment and facilitate the building of software collections and search engines dedicated to a specific scientific domain or topic.

For these reasons, we created the BioShaDock registry that promotes the use of container technologies in bioinformatics. The BioShaDock registry provides a web entry point to deploy, search and discover ready to use bioinformatics tools, encapsulated in Docker containers.

Future works will focus on better integration with domain-centric registries as well as bioinformatic integrated environments, to enable the seamless discovery, integration, and execution of the BioShaDock containers. Our project will also greatly benefit from discussions with other existing bioinformatic container initiatives.

The aim of BioShaDock is to contribute to the aggregation and standardization of bioinformatic tools and utilities. Maintaining ready to use validated and versioned software is key in ensuring the reproducibility needed in an open science approach.

Thereby, the creation of a collection of tools embedded in Docker containers, as provided by BioShaDock, is a pragmatic solution to this major bottleneck.

A number of other projects also focus on the provision of bioinformatic Docker images. BioDocker ³⁰ is a community based initiative to encourage the use of Docker images in bioinformatics. A GitHub repository stores a list of Dockerfiles that define the construction of images for the corresponding bioinformatic tool, with an open yet controlled contribution mechanism. Bioboxes ³¹ is an open source project that defines guidelines to build bioinformatic tool images using compatible interfaces for images which perform the same task, independent of the underlying tool, hence favoring interoperability between tools. It is therefore, among other characteristics, very well suited to automate tool and pipeline benchmarks. It has been applied to the assessment of different types of NGS data processing methods that concern assembly software as well as metagenomics tool. Dockstore ³² is an open platform that enables the registration of Docker images described using CWL. It integrates with a number of external services for source code and image hosting, and focuses on the provision of images that can be integrated in CWL-ready environments. BioShaDock shares with these existing efforts the use of Docker as a container technology to facilitate the distribution and integration of bioinformatic tools. However, none of these systems are designed to provide local image building and storage options. Furthermore, we believe the integration of BioShaDock with external domain-centric and platform-agnostic registries such as the ELIXIR registry will significantly raise the visibility of both the images provided and the container technology itself to the community of bioinformatic tool users. Because the files that describe the image building process (Dockerfiles) are usually freely available online, the interoperability issues between Docker registry initiatives are potentially very limited.

Computer scientists and bioinformaticians can more easily disseminate their programs and find potential users using a dedicated domain-centric Docker registry. There is a wide range of perspective uses for container registries in bioinformatics: repositories managed at a community level, based on tools embedded in containers, promote the ability to exchange and replicate data analyses.

In addition, the association between workflow models, data references and containerized tools could lead to the creation of interoperable and ready to use analysis components and pipeline collections maintained by many contributors. The development of such specifications is already in progress as illustrated by the CWL (Common Workflow Language) ²⁰ and the A-SCDFM (Autonomous Semi-Concrete Data Flow Model) ³³ portable workflow formats that are natively compatible with containers. In this case, the integration of programs in a container registry like BioShaDock and the formalization of the data processing following one of these new portable workflow specifications could simplify the creation of reproducible benchmarks, teaching material, demos and the production of use case prototypes. It could also be used by article reviewers to quickly evaluate a software.

The spread of container usage in the bioinformatics community and their indexing in repositories can be a solution to capture and share a large collection of data analysis methods. A wide set of bioinformatics components available on demand could induce better data analysis by simplifying tests and benchmarks.