What metrics should I track to know my deployment pipeline is healthy?

The main metric to watch is the pipeline execution time. This provides a baseline and any deviation can signal a warning or failure of a infrastructure component. As a deployment pipeline can touch and rely on multiple infrastructure components, it is a useful indicator of infrastructure health.

Another metric to watch is wait time. this is the amount of time the pipeline had to wait before being executed. A long wait time is an indicator that the build and deploy infrastructure is under resourced or broken.

You might want to track the deployment failures vs deployment success. This can give you a glimpse into your code quality. Improving code and tests will improve this statistic.

As a starting set, track these three per pipeline: execution time (baseline plus deviation), queue/wait time before a run starts, and the pass/fail ratio — trending any one of them weekly tends to surface infrastructure or code-quality problems before they cause an outage.