How does airflow find its compontents?

[static-moonlight]

I'm still in the process of building my Kubernetes deployment for Apache Airflow. I just added the triggerer and the web interface from the API server immediately shows this:

How does that work? I didn't tell the API server where to find the triggerer. I didn't tell the triggerer where to find the API server. And yet, they seem to find each other just fine and are already best buddies. How does this work? The only thing they have in common is the database. By any chance, is Airflow using its database as a service discovery middleware or something? Can someone explain to me how Airflow discovers its components? :)

[static-moonlight]

Nevermind. The database seems to be in fact a service registry. I found the entries I was looking for in the job table.

[apoorva-01]

Your hunch is right. The metadata DB is the coordination point, there's no direct network discovery between components.

Every long-running Airflow process (scheduler, triggerer, dag processor) writes a row into the job table (airflow.jobs.job.Job) when it starts up, with its hostname and a heartbeat timestamp, and then keeps bumping that timestamp on an interval. That's the whole "registry." Nobody tells the API server where the triggerer is. The API server just reads the job table and looks at latest_triggerer_heartbeat: if the newest one is within the threshold (30s by default) it shows healthy, if it's stale it shows down. Same mechanism for the scheduler.

So they're not really talking to each other at all. They each connect to the same Postgres, write their own heartbeat, and read everyone else's rows. The DB is the message bus, which is exactly the entries you found.

(Airflow 3 detail: workers no longer hit the DB directly, they go through the Task Execution API on the API server. But the scheduler/triggerer heartbeating into the job table is unchanged.)