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services

README.md

Services

This directory contains sub-projects for tasks that are run as kubernetes services as well as the main Harmony server itself. Any module that runs as a server is here, whereas library type modules should be plced under packages. Not to be confused with Harmony services that operate on actual data, these tasks are associated with the inner plumbing of scheduling work-items, processing work-item updates, etc.

These projects provide Docker files for building images as well as kubernetes manifest yaml files that define the deployments and services. The manifests can be used with kubectl to deploy the services.

Creating a Task Service

The easiest way to create a new task service is to copy the work-scheduler directory to a new directory under this (services) folder, then modify the code to do what you want. work-scheduler is a small Nodes.js Express app that uses the Worker class/pattern as defined in app/workers.ts. The Express server provides a health check endpoint for kubernetes while the Worker performs the real work of the application.

For new services it may be useful to add a metrics route to this server so that Prometheus can scrape it to drive an HPA, but that is beyond the scope of this discussion.

The specific steps to create a new service are

  1. cd services
  2. cp work-scheduler <new service>
  3. Modify the code in the app and test directories to implement/test your service.
  4. Modify the Dockerfile, env-defaults, and config/service-template.yml files as well as the push scripts in the bin directory as needed.
  5. cd <new service>
  6. Build the Docker image with npm run build.
  7. Deploy the service with kubectl -n harmony apply -f ./config/service-template.yaml

For sandbox deployments you can use the push scripts in the bin directory combined with npm to build and deploy your image to AWS ECR:

  1. Set your AWS profile to the sandbox, e.g., export AWS_PROFILE=harmony-sandbox
  2. VERSION=<some-tag> npm run build (or VERSION=<some-tag> npm run build-m1 if you are building on a Mac M1/M2 machine).
  3. bin/push-image-aws-cli2 <some-tag>

The service can be run directly during development using npm run start-dev-fast rather than running it as a kubernetes service. This is much more convenient than continually building the Docker image and redeploying.