Docker Swarm Architecture

Compose 🐳

flowchart LR
    none["svc-swarm-node declares no service"]

Swarm 🐝

flowchart LR
    none["svc-swarm-node declares no service"]

Volumes

flowchart LR
    none["svc-swarm-node declares no volume"]

Condition	Effect
swarm, storage.backend: nfs, no nfs: false, role not pinned	shared over NFS
any one of those missing	node-local

All four conditions must hold, so pinning a role takes every one of its volumes node-local. Only the role’s primary entry counts as pinned here: a placement on any other service pins that service alone and leaves the backing of every volume unchanged. The chain is drawn rather than its result, because that coupling is what makes a placement change move data without saying so.

Dependencies

flowchart LR
    subgraph deps [Dependencies]
        dep_web_app_docs["web-app-docs 🐳🐝"]
    end
    subgraph role [svc-swarm-node 💻]
        svc_node["node"]
        svc_docs["docs"]
    end
    subgraph dependents [Dependents]
        dpt_svc_cache_package["svc-cache-package 🐳"]
        dpt_svc_registry_cache["svc-registry-cache 🐳"]
        dpt_svc_registry_docker["svc-registry-docker 🐳"]
        dpt_svc_swarm_manager["svc-swarm-manager 💻"]
    end
    dep_web_app_docs -. "0..1" .-> svc_docs
    svc_node -- "1:1" --> dpt_svc_cache_package
    svc_node -- "1:1" --> dpt_svc_registry_cache
    svc_node -- "1:1" --> dpt_svc_registry_docker
    svc_node -. "0..1" .-> dpt_svc_swarm_manager

Symbol	Meaning
1:1 solid	fixed relationship
0..1 dashed	conditional, enabled only in matching deployments
0..0 red	declared but turned off in this role
💻	deploys to the host
🐳	deploys under compose
🐝	deploys under swarm
❌	service explicitly turned off
⚙️	Ansible role dependency from meta/main.yml

Every dependency and dependent is listed; the graph is not truncated.