substrate/docs/glossary.md

Agent Substrate Glossary

This document defines the core terms used across Agent Substrate.

For how the pieces fit together, see the Architecture and API Guide.

Resources (declarative)

• ActorTemplate (ate API resource): the definition of an actor "class": the container image(s) and snapshot configuration. Creating an ActorTemplate triggers creation of a Golden Snapshot. It is treated as immutable: you create a new template for a new version rather than editing an existing one. It is analogous to a Pod template, but for a checkpointable workload. ActorTemplates are created and managed through the substrate gRPC API (e.g. kubectl ate create actor-template) and stored in the control-plane database; they are not Kubernetes objects.

• WorkerPool (Kubernetes CRD): declares warm compute capacity, a fleet of pre-started worker pods. It is reconciled into a Kubernetes Deployment by the atecontroller.

• SandboxConfig (Kubernetes CRD): a cluster-scoped resource holding the sandbox binaries for one runtime family (the gVisor runsc binary, or a micro-VM kernel/firmware/config), plus the pause image for the sandbox's root container. An actor resolves its sandbox at first cold boot from the config its ActorTemplate names (naming one is currently required; per-class cluster defaults are planned), so one config pins the runtime version for many templates.

Records (dynamic state, in the control-plane store)

These live in the control-plane database because they change too frequently for etcd.

• Atespace: the isolation boundary an Actor belongs to, and the first half of its identity: an Actor is addressed by (atespace, name), so the same name can exist in two atespaces. Atespaces are global-scoped, not Kubernetes namespaces — an ActorTemplate also lives in an atespace, while WorkerPools live in Kubernetes namespaces. One must exist before any Actor can be created in it, and it can only be deleted once empty.

• Actor: a single instance derived from an ActorTemplate, identified by a DNS-1123 name. It is the unit that is suspended and resumed, and it moves between workers over its lifetime. An Actor record tracks its lifecycle status and snapshot references.

• Worker: a record representing one worker pod in a WorkerPool. A Worker hosts several Actors at once, each in its own sandbox, up to its actor limit and its compute capacity; many more are multiplexed across a pool over time.

Components

• ate-api-server (binary ateapi): the control plane. It owns the Actor lifecycle, schedules Actors onto Workers, and coordinates their snapshots, all backed by the state store. The kubectl-ate CLI talks to it.

• atecontroller: the Kubernetes controller that reconciles the CRDs (for example, it turns a WorkerPool into a Deployment).

• atelet: the node-level supervisor, run as a DaemonSet. It pulls images, assembles OCI bundles, drives the sandbox lifecycle on the node via ateom, and streams snapshots to and from snapshot storage.

• ateom: the coordinator that runs inside each worker pod and drives the sandbox runtime on behalf of atelet. This decouples the physical pod lifecycle from the sandboxed agent process. It embeds a networking service called atunnel that handles network traffic for the sandboxed Actor.

• atenet: the networking stack. Its router resumes suspended Actors on demand and routes traffic to the right worker pod.

• podcertcontroller: issues short-lived pod certificates that components use as their TLS identity to authenticate connections to one another (mutual TLS).

• kubectl-ate: a kubectl plugin CLI for managing the Actor lifecycle and listing Workers.

Lifecycle

• Suspend: hibernate a running or paused Actor into a durable snapshot in external storage. A running Actor is checkpointed on its Worker (which is then freed); a paused Actor's node-local snapshot is uploaded — narrowed to the commit scope when the pause captured more — ending its node pinning.

• Pause: a short-term checkpoint of a running Actor. Snapshot files remain on the node VM, and the following Resume is prioritized onto the node VM where the snapshots are persisted.

• Resume: activate a suspended/paused Actor by restoring it onto a Worker. The common path restores from a snapshot rather than cold-booting.

Volumes

• DurableDir volume: a directory mounted into one or more containers whose contents are preserved by the Data snapshot scope and therefore survive across Suspend/Resume independently of process memory or other rootfs writes. A volume may be mounted into multiple containers, potentially at different paths. This is the per-Actor application-data surface.

  How many an ActorTemplate may declare depends on its sandboxClass: a microvm template may declare several (they are subdirectories of one virtio-fs share, so they cost nothing extra per volume), while a gvisor template is limited to one until gVisor can accept more than a single durable mount.

Snapshots

• Snapshot scope: what an ActorTemplate's SnapshotConfig includes in a given snapshot. Two scopes exist today:

  • Full: process memory plus the rootfs delta on top of the OCI image, and any attached DurableDir volumes. Used to capture everything needed to resume hot.
  • Data: only the contents of attached volumes that support snapshots — currently DurableDir volumes. Process memory and the rest of rootfs are discarded. Used to persist application data cheaply without the cost of a full memory image. How the Actor comes back on Resume is governed by the Resume sources (onResume.fromData): cold-boot by default, or combined with the Golden Snapshot.

  Scopes describe only what a snapshot captures. They are configured per-trigger via onPause and onCommit: onPause selects what is captured during a Pause (kept on the node), and onCommit selects what is captured during a Suspend (uploaded to snapshot storage). onCommit must be a subset of onPause.

• Resume sources: an ActorTemplate's onResume block selects, per snapshot situation, what supplies the guest state on Resume. Each field names what is being resumed from; the value names the boot source. onResume.fromData applies when the Resume uses a Data-scope snapshot (from either trigger):

  • ColdBoot (default): start the containers afresh from the OCI image with the DurableDir contents restored.
  • Golden: restore the template's Golden Snapshot (process memory + rootfs delta) and serve the Actor's DurableDir data to it, so the Actor resumes with the golden's warm state over its own data. Currently microvm-only.

  A still-valid Full snapshot always restores from its own content and is not configurable here.

• Golden Snapshot: the initial checkpoint captured once, when an ActorTemplate is created, from a temporary "golden" boot of the workload. By default an Actor of that template is first restored from this shared snapshot. It is always a Full capture, and under onResume.fromData: Golden (see Resume sources) it also supplies the guest state that an Actor's Data snapshot is combined with on Resume.

• Last Snapshot: the most recent per-Actor snapshot, written on Suspend and used to restore that specific Actor on the next Resume.

• Snapshot storage: the object store (GCS or S3) where snapshots are persisted so Actor state is durable and portable across the cluster.

Networking

• Actor routing header: a higher-order system sends traffic to the Substrate router with ate-target-actor: <atespace>/<actor>. The router uses this header to locate and resume the Actor.