Why My Spark Container Keeps Exiting — Docker PID 1 and the Daemon Trap

I spent an embarrassing amount of time staring at my terminal, watching Spark containers start and immediately die. Three different attempts, three different failure modes, all in the same afternoon. If you're setting up Spark inside Docker and your container just... vanishes, this post is for you. The Setup I'm building a CMS Medicare streaming pipeline — pulling hospital charge data from the CMS public API, pushing it through Kafka, processing it with Spark Structured Streaming, and landing th