description CoreOS Fleet Overview
CoreOS Fleet was a cluster-management system for CoreOS environments, created to schedule and supervise systemd-based services across groups of machines. Operators described desired services in unit files or JSON manifests, and Fleet used the cluster's available hosts to place those units while tracking their state. It was aimed at distributed application deployment, including container workloads, but it is a legacy technology rather than a current general-purpose orchestration standard.
help CoreOS Fleet FAQ
What was CoreOS Fleet actually used for?
Fleet scheduled and supervised systemd services across a cluster of CoreOS machines, using etcd to coordinate cluster state. Operators wrote unit files or JSON manifests, flagging services as global or machine-specific, and Fleet placed them on available hosts.
Is CoreOS Fleet still maintained?
No, Fleet was deprecated as CoreOS shifted its container-orchestration focus to Kubernetes, a process that played out around 2016 to 2017. The project has been effectively unmaintained since, and new deployments should not be built on it.
What replaced CoreOS Fleet?
Kubernetes became the recommended scheduler, and CoreOS offered its own Kubernetes distribution called Tectonic as the migration path. Fittingly, etcd, which Fleet used internally, went on to become Kubernetes' standard datastore.
Why use Fleet instead of plain systemd on CoreOS?
Plain systemd only manages services on a single host, whereas Fleet extended those same unit files across a cluster, handling placement and failover between machines. For small CoreOS clusters it was a lightweight step up before full orchestrators took over.
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