CONCEPT Cited by 1 source
Desired-state reconciliation¶
Definition¶
Desired-state reconciliation is the control-plane pattern of continuously comparing the declared desired state (what should exist) against the observed actual state (what does exist), and applying corrections to close the gap. The loop runs perpetually — it is not a one-shot provisioning step but an ongoing process that converges reality toward intent.
Zak van der Merwe (EC2 / DSQL, AWS) uses the thermostat analogy: "It's a continuous loop, watching the state of the world, comparing it to what should be true, and correcting the difference." (Source: sources/2026-08-04-allthingsdistributed-on-building-scalable-control-planes)
Properties¶
- Level-triggered, not edge-triggered. The loop reacts to state differences, not events. If an event is lost, the next reconciliation pass still detects the drift. This makes the system self-healing without reliable event delivery.
- Idempotent corrections. Each reconciliation step must be safe to retry — applying the same correction twice should not cause harm.
- Convergent. Given enough passes, the system converges even if transient failures prevent individual corrections from landing immediately.
Seen in¶
- systems/ec2-control-plane — "When you launch a VM, the control plane records that a VM should exist, finds a physical server… Later, if that server disappears for any reason, the control plane notices and updates its records to reflect reality." (Source: sources/2026-08-04-allthingsdistributed-on-building-scalable-control-planes)
- Kubernetes controllers — the entire kube controller-manager is a set of reconciliation loops (ReplicaSet controller, Deployment controller, etc.).
- AWS CloudFormation / CDK — drift detection + stack update as reconciliation.
- GitOps (Flux, ArgoCD) — continuously reconciling cluster state with a git repo.
Relationship to static stability¶
Desired-state reconciliation depends on concepts/static-stability: if the reconciler fails, the system should remain operational in its last-known-good state until the reconciler recovers and the loop resumes.