Gera Tools

Docker Swarm Stack File Builder

Generate a Docker Swarm stack file with services, secrets, and constraints

Build a Docker Swarm compose v3.8 stack file with replicas, placement constraints, rolling update config, restart policy, resource limits, external secrets, and an overlay network. Runs entirely in your browser.

How is a Swarm stack file different from a plain compose file?

A stack file uses the same compose syntax but adds a deploy section that only Swarm reads — replicas, placement, update_config, restart_policy, and resources. docker compose up ignores deploy, while docker stack deploy honors it and runs the services across the cluster.

A Docker Swarm stack file builder that generates a docker stack deploy-ready compose v3.8 file. Each service gets a full deploy block — replicas, placement constraints, a safe rolling-update policy, restart rules, and resource limits — plus external secret references and an overlay network tying the cluster together.

How it works

A stack file looks like a compose file but adds a deploy section that only Swarm interprets. For every service the builder emits replicas, an optional placement.constraints list, and an update_config using order: start-first with failure_action: rollback so deploys add capacity before removing it and self-heal on failure. A restart_policy retries failed tasks, and a resources block sets CPU and memory limits and reservations.

Secrets you list per service are referenced under each service and collected into a top-level secrets: block marked external: true — meaning you create them once in the cluster with docker secret create and never store their values in the file. All services join a single top-level overlay network so they can reach each other by name across nodes.

Tips and notes

  • Run docker stack deploy on a manager node. Workers cannot deploy stacks, and the overlay network requires Swarm mode to be active.
  • Create secrets first: echo "value" | docker secret create db_password -. The external: true reference will fail to deploy if the secret does not already exist.
  • Keep update_config.parallelism at 1 for stateful services so you never take down more than one replica at a time; raise it for stateless services to deploy faster.
  • Placement constraints are AND-ed together. Use node labels (docker node update --label-add tier=app node1) to target specific hardware tiers cleanly.