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Database role

The database role makes sure a Node can run Docker. It marks the Node as a host for shared database Processes. The role owns no database container: shared MySQL or Postgres containers are Node Processes. A Node without this role can still run such a Process when Docker is present. The database connection registry does not need the role either.

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Add and converge

Add the role to an active Node:
node is a numeric ID or a Node name. Retry a failed or active assignment with --converge. node:add --role=database assigns the role during provisioning. Convergence installs the Ubuntu docker.io package, unless Docker CE is already installed and its docker service runs. The Gateway creates no Tool for Docker. The role accepts no options: a request with any other member, such as settings, fails with validation.failed. Add, converge, and remove only ensure Docker. They do not change Router configuration, existing Docker services, or Process ownership.

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Shared Nodes

The role shares a Node with app-dev, router, metrics, websocket, and analytics, in either order. It never shares a Node with gateway, vpn, ingress, or app-prod. A conflicting request fails with validation.failed before it changes anything. Role compatibility lists every pair.

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Remove

Remove the role with the generic role command:
Removal deletes the assignment. Docker, its service, and every Node Process stay on the Node. --purge-data changes nothing more. While the assignment is active, Doctor expects Docker to be installed and the docker service to run.

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Why it works this way

These reasons explain the design. Check them before you propose a change.

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Processes own the containers

Node Processes already own the lifecycle of Docker containers on a Node. A role that also owned database containers would give them two owners. So the role only ensures Docker.

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Removal keeps Docker

Processes on the Node can still use Docker after the role is gone. Removing Docker would break them.

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The remaining conflicts

gateway, vpn, ingress, and app-prod are dedicated control-plane, network, public, or production Nodes. A shared database host does not belong on them. router has no such reason, so the role shares a Node with it.