Learning term
Placement constraint — Compose, Swarm, and Portainer
Placement constraint restricts tasks to nodes with matching roles or labels. This card shows its role in “Compose, Swarm, and Portainer” and a safe diagnostic path.
Orientation
Placement constraint restricts tasks to nodes with matching roles or labels. At this level, separate purpose, input, and visible result. Place Placement constraint within Compose, Swarm, and Portainer before changing settings or files.
Practical use
Compare the constraint and node labels when a task remains pending. Start in a sandbox with neutral examples. Record the expected state, make one controlled change, and compare status output, application behavior, and logs.
Technical understanding
Placement constraint restricts tasks to nodes with matching roles or labels. Technically, Placement constraint connects through interfaces, configuration, state, or dependencies. Trace data from input to output and check versions, permissions, networking, storage, and resources separately.
Operations and debugging
Compare the constraint and node labels when a task remains pending. In production-like operations, use measurable signals, least privilege, reproducible configuration, and a documented rollback. Preserve evidence, isolate the cause, and verify the correction with the same test.
Exercise
Try it safely
Compare the constraint and node labels when a task remains pending. Open an isolated test environment and run “docker service ls && docker service ps example-service”. Write down the expected output first, do not alter production data, and record one safe next diagnostic step.
docker service ls && docker service ps example-serviceQuick check
Can you explain the purpose, observable state, and most common failure source of Placement constraint — Compose, Swarm, and Portainer in one sentence each? Which evidence would you preserve before changing anything, and which repeated test would prove that the correction actually worked?