This Go web application queries our internal HaProxy's for available services via REST HaProxy then queries all available backend services on their management endpoints for running services. It then compares this to the versions mapped in configuration management (we use puppet, and expose a single hieradata file called versions.yaml, which is managed by Jenkins via a webhook on our Puppet master).
If the versions running or mapped in configuration management are the same, the service is green; if not, the service is red. This gives us vital visability into the state of a given deployment across all nodes and processes.