Enabling numerical Models as a Service (MaaS)

Running numerical models you are unfamiliar with is not always straightforward. The models have different kinds of interfaces, different program languages, and different names for the same concepts. To standardize this, the Basic Model Interface (Hutton, 2020) was developed by the Community Surface Dynamics Modeling System (CSDMS). With the Basic Model Interface (BMI), users are presented with a standard set of functions to query and control numerical models. This standard interface also allows users to couple models together, allowing for the creation of standard components that can be coupled to create a full model (Peckham, 2013). 

However, coupling these models or components, whether they are written in C, C++, Fortran or Python, requires them to all share the same interpreter or (Python) environment. This is not always possible or viable and can require compilation on the end-user's side. This also prevents containerization of models. 

For cross-language and cross-container communication we developed grpc4bmi in 2018, making it possible to use the BMI over a HTTP connection. However, while highly performant, gRPC is not supported in many languages. To this end, we developed the new RemoteBMI protocol. RemoteBMI can communicate to models using the Basic Model Interface using a RESTful API, making it easier to support any language; only a HTTP server and JSON parser implementation are required. 

With grpc4bmi and RemoteBMI it is possible to package a model or model component inside a software container (e.g., Docker) and communicate with these models over an HTTP connection. This makes models more interoperable and reproducible, as container images can easily be archived and used by other people. It also enables running models on different machines than your own, and then directly communicating with them or coupling them to other models. 

With these technologies, you can now, for example, host models that require specific and difficult-to-share input data and provide them to anyone interested as a web-based service. This model-as-a-service (MaaS) architecture could also make it easier for end-users to try out your model in the browser before committing to installing it locally if they are interested. 

Currently, the grpc4bmi and RemoteBMI protocols are used by the eWaterCycle platform (Hut, 2022), allowing hydrologists and students easy access to containerized hydrological models through a common interface, accelerating both research and teaching. 

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Hutton, E.W.H., Piper, M.D., and Tucker, G.E., 2020. The Basic Model Interface 2.0: A standard interface for coupling numerical models in the geosciences. Journal of Open Source Software, 5(51), 2317, https://doi.org/10.21105/joss.02317. 

Peckham, S.D., Hutton, E.W., and Norris, B., 2013. A component-based approach to integrated modeling in the geosciences: The design of CSDMS. Computers & Geosciences, 53, pp.3-12, http://dx.doi.org/10.1016/j.cageo.2012.04.002. 

Hut, R., et al. (2022). The eWaterCycle platform for open and FAIR hydrological collaboration. Geoscientific Model Development, 15(13), 5371–5390. https://doi.org/10.5194/gmd-15-5371-2022