Billing API

Tools to generate Invoices based on usage.

Idea:

This application should be able to programmatically measure resource usage (CPU/Memory/Storage) via Prometheus & Loki on a per-tenant basis and generate the appropriate InvoiceNinja invoices.

Needed endpoints:

• List clients
• Get client by name
• Create new client
• Generate Invoice
• Get start + end time for service/resource (Loki K8s event log)
• Get usage over period for metric
• Generic LogQL Query
• Push generated cost data back to Promtheus/Loki

Components

• http-swagger: generates testable API docs
• Chi: FastAPI-like framework for golang
• Yq: Query JSON/YAML data without needing structs.
• Go-Invoice-Ninja: Interact with Invoice-Ninja using Go.
• Prometheus/client_golang: Query usage metrics from the observability stack

Endpoints:

• Docs: http://localhost:3000/swagger
• Metrics: http://localhost:3000/metrics
• Ready: http://localhost:3000/ready

Docker

kubectl port-forward svc/mimir-gateway 8080:80 \
    -n monitoring \
    --address 192.168.1.201

kubectl port-forward svc/loki-query-frontend 3100:3100 \
    -n monitoring \
    --address 192.168.1.201

kubectl port-forward svc/smol-invoiceninja-nginx 8888:80 \
    -n default \
    --address 192.168.1.201

docker build . -f Dockerfile -t billing-api

docker run -it -p 3000:3000 \
    -e PROMETHEUS_ENDPOINT="http://192.168.1.201:8080/prometheus" \
    -e LOKI_ENPOINT="http://192.168.1.201:3100" \
    -e INVOICE_NINJA_ENDPOINT="http://192.168.1.201:8888" \
    -e INVOICE_NINJA_API_KEY="" \
    -e LOKI_QUERY_LINE_LIMIT="100" \
    billing-api

Development

1. Install deps:

   • Install Go: https://go.dev/doc/install

   • Install Chi:

     go get -u github.com/go-chi/chi/v5
     

   • Install http-swagger:

     go install github.com/swaggo/swag/cmd/swag@latest
     

2. Set required Env Vars:

   export PROMETHEUS_ENDPOINT="http://127.0.0.1:8080/prometheus"
   export LOKI_ENDPOINT="http://127.0.0.1:3100"
   export INVOICE_NINJA_ENDPOINT="http://127.0.0.1:8888"
   export INVOICE_NINJA_API_KEY=""
   export LOKI_QUERY_LINE_LIMIT="100"
   

3. Run swag init --parseDependency --parseInternal -g main.go to generate docs

4. Run go build to build the program

5. Run go run main.go to start the server on localhost:3000