# PostHog's architecture - Docs

This section covers PostHog's [data model](/docs/how-posthog-works/data-model.md), [ingestion pipeline](/docs/how-posthog-works/ingestion-pipeline.md), [ClickHouse setup](/docs/how-posthog-works/clickhouse.md) and [data querying](/docs/how-posthog-works/queries.md). This page provides an overview of how PostHog is structured.

## Broad overview

PostHog has a few main systems:

-   **Web app and API** – Django serves the UI and REST API for users
-   **Rust microservices** – High-throughput services for event capture, feature flag evaluation, and session replay ingestion
-   **Kafka** – Central message bus connecting ingestion to storage
-   **Background workers** – Celery (short tasks), Temporal (reliable workflows), and Dagster (scheduled data pipelines)
-   **CDP** (Customer Data Platform) – Processes events on ingestion and exports to destinations

graph LR sdk\[Client Apps/SDKs\] u\[User\] ex\[Export destinations\] capture\[Capture services<br/>Rust\] web\[Web/API<br/>Django\] cdp\[CDP<br/>Node.js\] workers\[Background workers<br/>Celery · Temporal · Dagster\] kafka{{Kafka}} ds\[(Data stores<br/>ClickHouse · PostgreSQL · Redis · Blob storage)\] sdk -->|events & recordings| capture sdk -->|feature flags| capture u --> web capture --> kafka kafka --> cdp cdp --> kafka kafka --> ds cdp --> ex web <--> ds workers <--> ds web --> workers

## Zooming closer

Adding detail reveals the individual services and how data flows between them.

graph TD u\[User\] --> web\[Django web app / API\] sdk\[Client Apps/SDKs\] -->|events| cap\[Capture\] sdk -->|flags| flags\[Feature flags\] sdk -->|recordings| replay\[Replay capture\] web <--> redis\[(Redis)\] web --> workers\[Background workers<br/>Celery · Temporal · Dagster\] cap --> kafka{{Kafka}} replay --> kafka replay --> blob\[(Blob storage)\] kafka --> cdp\[CDP worker\] cdp -->|processed events| kafka cdp --> ex\[Export destinations\] web <--> ch\[(ClickHouse)\] workers <--> ch kafka --> ch web <--> pg\[(PostgreSQL)\] workers <--> pg flags <--> pg cdp <--> pg

## Infrastructure view

On PostHog Cloud, the application services run in an EKS (Kubernetes) cluster on AWS, while the data stores are managed separately.

flowchart TD ClientApps("Client Apps / SDKs") --> ALB subgraph EKS \["EKS cluster (Kubernetes)"\] ALB --> Django\["Django (web app, API)"\] ALB --> Rust\["Rust services<br/>(capture, feature flags, replay)"\] Workers\["Background workers<br/>(Celery, Temporal, Dagster)"\] CDP\["CDP worker (Node.js)"\] end Django <--> Redis\[("Redis / Valkey")\] Rust --> S3\[("S3 (recordings, exports)")\] Rust --> Kafka{{Kafka / WarpStream}} Kafka --> CDP CDP --> Kafka Django --read path--> CH Workers --read path--> CH Kafka --write path--> CH subgraph CH \["ClickHouse cluster (self-managed EC2)"\] direction LR S1\["Shard 1<br/>(Replica A · Replica B)"\] ~~~ SN\["... Shard N<br/>(Replica A · Replica B)"\] end CH -.- ZK\[ZooKeeper\] Django --> PgBouncer Workers --> PgBouncer CDP --> PgBouncer PgBouncer\[PgBouncer\] --> PG\[("Aurora PostgreSQL")\]

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