Health Check of CAP Library— CAP.HealthCheck

Microservice architectures frequently use asynchronous communication. One service can send an asynchronous message to another service using the message broker, such as RabbitMQ or Kafka. The outbox pattern is one of the standard solutions in this architecture. CAP is a library based on .NET, which implements the outbox pattern described in the eShop ebook. In this pattern, published and received messages are stored on storage, such as MSSQL or PostgreSQL. In addition, each message has a state which is Succeeded or Failed. It is essential to monitor storage and message broker connectivity and failures. Otherwise, data inconsistencies may occur in the system. In this article, CAP.HealthCheck, a health check library developed for the CAP, will be introduced.

CAP.HealthCheck library

It is available at NuGet. CAP HealthCheck can be installed in the project with the following command:

PM> Install-Package DotNetCore.CAP.HealthCheck

Storage health checks

Currently, it supports PostgreSQL and MongoDB as storage health checks. To install:

PM> Install-Package DotNetCore.CAP.HealthCheck.PostgreSql
PM> Install-Package DotNetCore.CAP.HealthCheck.MongoDB

They have several health check services that check database connectivity and failed data count in published and receive tables. If failed counts are zero and the connection is successful, it returns healthy, otherwise unhealthy.

Transport health checks

Currently, it supports only RabbitMQ as transport health checks. To install:

PM> Install-Package DotNetCore.CAP.HealthCheck.RabbitMQ

It has only broker connectivity health check for now.

Configuration

Usage and configuration are easy as a .NET health check service. They are added in ConfigureServices method without specifying parameters like below:

Health check services are easily accessible at route /health-cap by default. The code below is used to enable and configure the route.

Example Output

{
  "status": "Unhealthy",
  "results": {
    "cap.postgres.connection": {
      "status": "Healthy",
      "description": null,
      "duration": "00:00:00.0669333",
      "tags": [
        "cap"
      ],
      "data": {}
    },
    "cap.postgres.publishedtable": {
      "status": "Healthy",
      "description": null,
      "duration": "00:00:00.0282225",
      "tags": [
        "cap"
      ],
      "data": {
        "failedCount": 0,
        "succeededCount": 1
      }
    },
    "cap.postgres.receivedtable": {
      "status": "Unhealthy",
      "description": "Failed Count: 1",
      "duration": "00:00:00.0407061",
      "tags": [
        "cap"
      ],
      "data": {
        "failedCount": 1,
        "succeededCount": 0
      }
    },
    "cap.rabbitmq.connection": {
      "status": "Healthy",
      "description": null,
      "duration": "00:00:00.0042972",
      "tags": [
        "cap"
      ],
      "data": {}
    }
  }
}

Sample Applications

The github repository contains sample applications, and they have their docker compose file to run required infrastructures. Sample applications have a controller named Test with route api/test.

There are two endpoints for publishing an event with success and failure scenarios.

• http://localhost:5000/api/test/publish publishes an event with successful subscription.
• http://localhost:5000/api/test/publish/error publishes an event with failed subscription.

The healthcheck service is available at http://localhost:5000/health-cap.

Repository

Source code is available at github:

GitHub - teomane/CAP.HealthCheck: The health check library of CAP.

Future Works

This project will continue with the addition of health check services for all the features of the CAP library.

Our articles about CAP

Eventing with Inbox/Outbox Patterns in Microservices — CAP Library

Event bus implementation using EF Core and CAP libraries

Using CAP library in multi-tenant application via SubscribeFilter

Thanks for reading.