Docker Swarm in 2026's swarm already placed BookNest's tasks, replaced failed ones and rolled out updates. Three gaps showed even in that lab. Every API replica ran CREATE TABLE IF NOT EXISTS at startup, and in two of four runs two replicas raced and one crashed; Swarm 514 has no "run once to completion first" object, while Kubernetes 5,150 has the Job and the init container. Swarm's only health signal is HEALTHCHECK; Kubernetes separates liveness (restart me) from readiness (no traffic yet), which is why BookNest has both /health and /ready. And Swarm's feature set is fixed, while Kubernetes accepts new object types through custom resources and controllers (Operators and CRDs).
Then there is the ecosystem: managed control planes on every cloud, Helm 29,435 , GitOps controllers, autoscalers and operators. Swarm remains a sound choice for a few hosts and a small team, but new tools target Kubernetes first.