> ## Documentation Index > Fetch the complete documentation index at: https://docs.goakt.dev/llms.txt > Use this file to discover all available pages before exploring further. # Architecture Overview > System design and component diagram. ## Bird's eye view GoAkt is a framework for building **concurrent, distributed, and fault-tolerant systems** in Go using the actor model. Every unit of computation is an **actor**—a lightweight, isolated entity that communicates exclusively through messages. The [Actor System](/actor/actor-system) is the top-level runtime that hosts actors and orchestrates messaging, clustering, and lifecycle. ## Three deployment modes | Mode | Description | | -------------------- | ----------------------------------------------------------------------------------------------------------- | | **Standalone** | Single process. Actors communicate in-process. | | **Clustered** | Multiple nodes. Discovery via Consul, etcd, Kubernetes, NATS, mDNS, or static. Location-transparent actors. | | **Multi-Datacenter** | Multiple clusters across DCs. Pluggable control plane (NATS JetStream or etcd). DC-aware placement. | ## Core building blocks | Concept | Role | | --------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | **Reactive stream** | Composable `stream.Source` → `Flow` stages → `Sink` pipelines, materialized with `RunnableGraph.Run` on an `ActorSystem`. Stages run as actors with demand-driven backpressure. See [Streams](/advanced/streams). | | **CRDT / Replicator** | Conflict-free replicated data types (`crdt` package), merged by a per-node **Replicator** system actor. Replication is **eventually consistent**—separate from the Olric actor/grain registry (quorum-strong). See [Distributed data](/advanced/distributed-data). | ## Message flow Message flow - Sender sends Tell (fire-and-forget) or Ask (request-response) to Receiver via local or TCP transport, messages enqueue to mailbox then dequeue to Receive For remote messages, the remoting layer serializes the payload over a custom TCP frame protocol with optional compression. ## Actor hierarchy Actor hierarchy - root guardian at top, /system branch for internal actors, /user branch for user-defined actors with nested children When a parent stops, all children stop first (depth-first). A parent supervises its children. ## Cluster architecture Cluster architecture - GoAkt Cluster Node with ActorSystem connecting to Cluster (Olric DMap), Discovery, Remoting (TCP/TLS), and TCP Server **Placement and membership** state (which actors and grains live where) is stored in Olric (distributed hash map) with configurable quorum. Node membership uses Hashicorp Memberlist. **CRDT application state** (when enabled via `ClusterConfig.WithCRDT`) is replicated separately by the **Replicator** actor using delta broadcast over the topic bus—not through Olric DMap writes. ## Deep dives The following pages describe the internal architecture of each major subsystem: | Subsystem | Page | What it covers | | ------------- | ------------------------------------------------ | --------------------------------------------------------------------------------------------------------------- | | **Scheduler** | [Dispatcher Pool](/architecture/dispatcher-pool) | Fixed worker pool, actor state machine, ready queue, work stealing, system-message priority, throughput tuning. | ## See also * [Code Map](/architecture/code-map) — package layout and file-level responsibilities * [Design Decisions](/architecture/design-decisions) — rationale behind architectural choices