Architecture of CHT Instances

The different pieces of a CHT project, how they interact, and what they’re used for

Overview

Architecture of a CHT project

Server

CHT Core Framework

The cht-core product is the primary component of the CHT. The server comes with authentication, role based authorization, data security, and a range of protected data access endpoints. Read more detail in cht-core GitHub repository.

API

A NodeJS service which runs on the server and provides security and APIs for browsers and integrations. It also includes a custom implementation of filtered replication to allow it to support more concurrent users. See more at the CHT Core API repo on Github.

Sentinel

Another NodeJS service running on the server, sentinel performs actions called transitions every time a document in CouchDB is added or modified. Some examples are validations, generating scheduled messages, automatic responses, creating patients, and sending alerts. See more at the CHT Core Sentinel repo on Github.

CouchDB

A free and open source NoSQL database used as the primary store for all app data and configuration. This can be multiple instances clustered together for additional scalability. CouchDB is really good at replication which is the process of sending the data to another database and back again, which makes it ideal for replicating data to the phone for offline access. See more at the CouchDB site.

NGINX

NGINX provides SSL termination and routes requests to API.

HAProxy

HAProxy provides audit logging for any request that makes it to CouchDB so any data access or modification can be validated at a later date.

CHT Upgrade Service

The CHT Upgrade Service is used within the CHT to update individual Docker containers when an upgrade is requested. Read more detail in the cht-upgrade-service GitHub repository.

CHT Sync

A suite of tools for extracting and normalizing data from the Core Framework’s CouchDB, and rendering the data in analytics dashboards to visualize key data for a CHT deployment. Read more detail in cht-sync GitHub repository.

Logstash and PostgREST

Logstash streams data from CouchDB and forwards it to PostgREST which provides REST endpoints to store the data in the PostreSQL database.

PostgreSQL

A free and open source SQL database used for analytics queries. See more at the PostgreSQL site.

DBT

DBT is used to ingest raw JSON data from the postgres database and normalize it into a relational schema to make it much easier to query.

Superset

Apache Superset is a free an open source platform for creating data dashboards.

Client

CHT Core Framework

The CHT Core Framework provides two web applications: the CHT Web App for care teams and program staff, and App Management for program administrators.

CHT Web Application

The CHT Web Application is used by Community Health Workers and provides a large variety of features. View the source code in our GitHub repository.

Technology

The CHT Web Application is reactive, responsive and a single page application built with Angular and NgRx frameworks. Additionally, it uses the following technology:

TechnologyUsage
PouchDBTo implement an Offline-First strategy which means the data is stored on the client and all pages can load immediately regardless of whether the user has a fast connection, slow connection, or no connection at all. The data is stored in PouchDB which replicates changes back and forth in the background with the server CouchDB.
EnketoTo render configured xforms and help with styling and dynamic elements such as show/hide and validation rules.
NoolsA rules engine to compute the upcoming tasks and monthly targets of the users.
Ngx-BootstrapTo integrate Bootstrap components in the Angular application.
Ngx-translateTo automatically translate the labels from a Angular application. Read more about how to configure translations.
KarmaA test runner for unit tests
MochaJSA test framework to run the unit tests
ProtractorTo run the e2e tests
LessA CSS preprocessor
Structure

The CHT Web Application has the following high level structure:

  • /js: Contains the vanilla JavaScript scripts, for example: Enketo widgets, MomentJS locales, etc.
  • /ts: Contains the Angular application source code which uses TypeScript.
    • /actions, /effects, /reducers and /selectors: Contain the implementation for the application’s reactive state which uses NgRx framework.
    • /components, /directives, /pipes, /providers and /services: Contain the reusable elements from Angular framework.
    • /modals: Contains the all application’s modals components.
    • /modules: Contains the application’s modules, each of them has components that are associated to the modules’ routing.
  • /css: Contains the style files. It uses Less as a CSS preprocessor.
  • /fonts: Contains the fonts.
  • /img: Contains the static images.

App Management

App Management is an interface for non-technical administrative users to manage users and settings.

View the application source code in our GitHub repository.

Technology

App Management is a single page application built with AngularJS framework and implements Redux to manage a reactive state. Additionally, it uses the following technology:

TechnologyUsage
Angular TranslateTo automatically translate the labels from a AngularJS application. Read more about how to manage translations.
KarmaA test runner for unit tests
MochaJSA test framework to run the unit tests
ProtractorTo run the e2e tests
LessA CSS preprocessor
Structure
  • /css: Contains style files. It uses Less as a CSS preprocessor.
  • /js: Contains the JavaScript code.
    • /actions, /reducers and /selectors: Contain the implementation of Redux.
    • /controllers, /directives, /filters and /services: Contain the reusable elements from AngularJS framework.
    • /modules: Contains the vanilla JavaScript scripts.
  • /template: Contains the HTML templates that are used in the AngularJS components and directives.

cht-android

CHT Web Application works in the browser or wrapped in the CHT Android app which allows for project branding, sets the project URL, and hides browser elements like the URL bar.

Other applications

cht-gateway

CHT Gateway is an android app for sending and receiving SMS messages. Each SMS enabled project has one gateway running. It polls an api endpoint to write incoming SMS into the CouchDB and retrieve outgoing SMS to send.

medic-collect

Medic Collect is an android app based on Open Data Kit to render xforms on the phone and send reports in to cht-gateway over SMS or directly to api over mobile data.

cht-conf

cht-conf is a command line utility for uploading configuration and bulk importing of records.