CHT Core

Technical overview of the CHT Core Framework

The CHT Core Framework 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.

  graph TB
  classDef container stroke:#63a2c6, fill:#eef5f9, color:#000
  
  subgraph CHT_Core_Framework["<div style="width: 23em; height:2em; display:flex; justify-content: flex-start; align-items:flex-end;">Server</div>"]
    direction TB
    NGINX(NGINX):::container
    API(API):::container
    Sentinel(Sentinel):::container
    HAProxy(Haproxy):::container
    HealthCheck(HealthCheck):::container
    CouchDB[(CouchDB)]:::container
    Nouveau[(Nouveau)]:::container
  end

  Upgrade["Upgrade Service"]:::container

  subgraph Client["<div style="width: 28em; height:2em; display:flex; justify-content: flex-start; align-items:flex-end;">Client (Android & Browser)</div>"]
    subgraph Webapp["Webapp"]
      PouchDB[(PouchDB)]:::container
    end

    Admin["App Management"]:::container
end
  
  Webapp --> NGINX
  Admin --> NGINX
  NGINX --> API
  API <--> Upgrade
  Sentinel --> HAProxy
  API --> HAProxy
  HAProxy --> CouchDB
  HealthCheck --> CouchDB
  HAProxy --> HealthCheck
  CouchDB --> Nouveau

  style CHT_Core_Framework fill: transparent
  style Client fill: transparent
  style Webapp fill: transparent

Server

API

A NodeJS service that 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.

Nouveau

Nouveau is a CouchDB service, added to the CHT in version 5.0.0, leverages the Lucene search engine to modernize how freetext searches are done. Nouveau is faster at running these queries and more efficient at storing and creating the indexes. Offline users do not use this.

NGINX

NGINX provides SSL termination and routes requests to API.

HAProxy

HAProxy provides logging and reverse proxying for any request that makes it to CouchDB.

HealthCheck

A service that periodically verifies the health status of the CouchDb cluster. HAProxy uses this service for checking server status.

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.

Client

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:

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:

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.

Data Flows

Without cht-datasource

  flowchart TD
subgraph webapp
  webapp/online[/Online User\]
  webapp/offline[/Offline User\]
  webapp/cht-datasource/offline/pouch[PouchDB]
end
subgraph api
  replication{Replication}
  api/router(( ))
end
couchdb[(CouchDB)]
replication -->|POST medic/_bulk_get| couchdb
webapp/offline --> webapp/cht-datasource/offline/pouch -->|/api/replication| replication
webapp/online --> webapp/cht-datasource/offline/pouch -->|GET <_id>| api/router
api/router --> |GET <_id>| couchdb

With cht-datasource

  flowchart TD
subgraph webapp
  webapp/online[/Online User\]
  webapp/offline[/Offline User\]

  subgraph webapp/cht-datasource[cht-datasource]
    webapp/cht-datasource/online/fetch[fetch]
    webapp/cht-datasource/offline/pouch[PouchDB]
  end
end
subgraph api
  subgraph api/cht-datasource[cht-datasource]
    api/cht-datasource/pouch[PouchDB]
  end
  replication{Replication}
end
couchdb[(CouchDB)]
api/cht-datasource/pouch -->|GET medic/<_id>| couchdb
webapp/offline --> webapp/cht-datasource/offline/pouch -->|/api/replication| replication
webapp/online --> webapp/cht-datasource/online/fetch -->|GET api/v1/person| api/cht-datasource
replication --> |POST medic/_bulk_get| couchdb

Replication algorithm (simplified)

  sequenceDiagram
    participant webapp
    participant api
    participant couchdb

    webapp ->>api: GET api/replicaiton/get-ids
    api ->>couchdb: Query view <br />medic/docs_by_replication_key
    couchdb ->>api: Returns docs for users hierarchy/shortcode
    api ->>api: Filter our purged docs
    api ->>webapp: Returns list of all doc ids/revs <br />accessible to the user
    webapp ->>webapp: Compares with ids of all local docs
    webapp ->>couchdb: POST medic/_bulk_get <br />(with the missing ids)
    couchdb ->> webapp: Returns requested docs
    webapp ->>api: POST api/v1/replication/get-deletes <br />(with local ids not returned from get-ids)
    api <<->> couchdb: Uses allDocs to check deleted status
    api ->>webapp: Returns list of docs to be deleted
    webapp ->>webapp: Deletes docs

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