@opensesame/course-authoring-library-service-check

Service Check Library

The service check library provides a HAPI based controller that creates endpoints can be used to serve a health check, a readiness check, a service check, and a dependency check.

Health Check

Purpose

The health check endpoint is used to monitor the status of a running container. These checks are used by Kubernetes to determine the current health of a given container, and is run constantly and often. This means that we need to be careful about the types of checks added - they should be quick, and should not strain dependency or outside resources. However, they should give a good understanding of the current health of the service.

Adding a check

To add a check, in the service that is consuming the library, create an async function that has no parameters and returns a Promise. Then, using the CheckController object that is created for your service, call the "AddHealthCheck" function. The function takes the name of the check (a string), the function you created (of type CheckFunction), and an optional timeout (a number in milliseconds that defaults to 200).

Calling the check

The endpoint will be at /api/health-check and should return a formatted JSON object

Readiness Check

Purpose

The readiness check endpoint is used by Kubernetes to determine whether a container is ready to take traffic. This endpoint should generally only be called during the initial deployment of a container, and once it returns "ready", the container will begin to take traffic. These checks are intended to help make sure that "slow loading" containers aren't killed by Kubernetes. They should focus on making sure that any resource that might take time to be "ready" to take on traffic is tested.

Adding a check

To add a check, in the service that is consuming the library, create an async function that has no parameters and returns a Promise. Then, using the CheckController object that is created for your service, call the "AddReadyCheck" function. The function takes the name of the check (a string), the function you created (of type CheckFunction), and an optional timeout (a number in milliseconds that defaults to 200).

Calling the check

The endpoint will be at /api/readiness-check and should return a formatted JSON object

Service Status Check

Purpose

The service status check provides system information about the environment that the code/container is running in. It can be used to report out useful metrics about the memory usage, for example, over time. The data reported by this endpoint cannot be modified by the consumer of the library.

Calling the check

The endpoint will be at /api/service-status-check and should return a formatted JSON object

Dependency Check

Purpose

The dependency check endpoint is intended to be used during deployment to make sure the necessary dependencies of the service are in place. These include things like API contracts (do the APIs I am calling have the right endpoint versions? Are the contracts for those versions what I expect?) as well as the availability of resources (Is the Amazon MQ Broker accessible? Can I hit the Postgres database?). These checks can be a little more costly, since they should be seldom hit.

Adding a check

To add a check, in the service that is consuming the library, create an async function that has no parameters and returns a Promise. Then, using the CheckController object that is created for your service, call the "AddDepencencyCheck" function. The function takes the name of the check (a string), the function you created (of type CheckFunction), and an optional timeout (a number in milliseconds that defaults to 200).