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SolarMonitorApi

Introduction

The SolarMonitorApi application forms part of the Solar Monitor Project.

The main purpose of the SolarMonitorApi is to persist solar measurements from various solar sites and to make this information available to different types of clients (web currently and mobile in the future) via a flexible RESTful API.

How to build

Prerequisites

  • .NET Core 2.0 SDK
  • MySQL server 5.7

Note: this project has been developed with VS Code. The solution may also work in Visual Studio 2017 Update 3 as long as .Net Core 2.0 SDK is installed.

Build instructions

  1. Restore dependencies: dotnet restore (in root folder)
  2. Build: dotnet build (in root folder)
  3. Run tests: dotnet test (in a folder containing a test project)

More detailed notes about the different developer tools and commands can be found here.

SolarMonitorApi Architecture

System Architecture

The SolarMonitorApi application is structured as shown above in 3 layers:

  1. API Layer

    This layer contains the main components that implement the APIs: Controllers, Middleware, Swagger related configuration classes, Filters, etc.

    There are 5 different controllers that form part of the SolarMonitor API:

    • SolarMonitor - provides general information such as server version.
    • Sites - information about the various solar sites in the system
    • Devices - describes various solar devices (such as Inverters, Charge Controllers, Solar Arrays, etc.)
    • Sensors - information related to the sensors in the system (shunts, current sensors, temperature and humidity sensors, sensors that hold energy statistical information, battery state of charge, etc.)
    • Measurements - measurement data produced at regular intervals by the sensors.

  2. Business Logic Layer

    Contains the Services as well as supporting classes (Model Binders, Validators, Request Query classes).

  3. Data Layer

    This layer contains the projects related to data access: Repositories, Data Models, REST Resources (i.e. DTOs), Adapters (for converting between Models and REST Resources). It also contains a MySQL implementation of the Repositories, which uses Entity Framework and the Pomelo MySQL EF Adapter to connect to the MySQL database.

    The project uses code-first database design. Models that belong the same category of entities (e.g. sensors or devices) are structured hierarchically. We map these hierarchies using the "Table per Hierarchy" mechanism, since it is the only mechanism supported by EF Core (as of 2.0). This means that for example the whole set of sensor related classes will be mapped to a single "Sensors" table in the database, with a discriminator column (SensorType) used by EF Core to automatically map the rows in the table to the correct Sensor-derived class.

Authentication and authorization

This application uses self-contained JWT tokens for API authorization. SolarMonitorApi does not issue tokens directly but it relies on another service (see the AuthService repo) to perform the actual authentication and to issue tokens. The AuthService is based on IdentityServer4 and supports standard Open Connect and OAuth2 protocols.

There are 2 levels of access based on roles:

  • 'user' role has access to all read-only APIs
  • 'admin' role has access to all (read and write) APIs

API Design

TBD

Hosting

Hosting is done in Linode (Linux-based cloud provider) via a shared VM. I highly recommend this service - it costs USD5 a month for a very reliable and fast (shared) VM.

Initially I hosted the SolarMonitorApi via an Azure Web App service. This had the advantage that it was very easy to set up and required no maintenance. However the cost was too high for what I needed. Given that the application cross-platform (being based on .Net Core), I went for Linode.

Testing strategy

The application contains tests at 3 levels, using xunit as the test harness:

Unit tests

These are class level tests. Mock classes may be used to stub out external dependencies - this is trivial as almost all classes in the system use dependency injection for their dependencies.

Integration tests

The integration tests form the bulk of the tests in the system. They are responsible for testing all APIs in a manner that very closely reflects the way the system is run in production, with 2 exceptions:

  • the tests run the full SolarMonitorApi application in-process, however the full ASP.NET pipeline is loaded and executed for every request. The tests use the standard HttpClient class to send request to the server, even though it runs in the same process. This is achieved using the test infrastructure provided by ASP.NET Core called TestHost.

  • the back-end MySQL database is substituted with an in-memory SQLite provider.

Each test is responsible for creating the database and populating it with the data that it needs and destroying it at the end. This means that tests are fully independent of each other and can be parallelised easily to make use of multiple cores.

The benefits of this approach is that the tests run very fast (under 1s per test including database set up and tear down) providing quick feedback on regressions while still exercising the full application stack.

System (end-to-end) tests

The system tests are true end to end tests where the system is set up identically to the production environment:

  • the SolarMonitorApi is hosted independently of the tests (in a Docker container)
  • an actual MySQL database is used
  • the external AuthService is also used for authentication and issuing tokens

This set of tests is fairly small. They are intended for validating the deployment procedure and to ensure everything is set up correctly while at the same time running some basic smoke tests to give enough confidence that everything is working as it should before pushing to production.