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The ATC is the heart of Concourse. It runs the **web UI and API** and is responsible for all pipeline **scheduling**. It **connects to PostgreSQL**, which it uses to store pipeline data (including build logs).
The [checker](https://concourse-ci.org/checker.html)'s responsibility is to continously checks for new versions of resources. The [scheduler](https://concourse-ci.org/scheduler.html) is responsible for scheduling builds for a job and the [build tracker](https://concourse-ci.org/build-tracker.html) is responsible for running any scheduled builds. The [garbage collector](https://concourse-ci.org/garbage-collector.html) is the cleanup mechanism for removing any unused or outdated objects, such as containers and volumes.
### TSA: worker registration & forwarding
The TSA is a **custom-built SSH server** that is used solely for securely **registering** [**workers**](https://concourse-ci.org/internals.html#architecture-worker) with the [ATC](https://concourse-ci.org/internals.html#component-atc).
The TSA by **default listens on port `2222`**, and is usually colocated with the [ATC](https://concourse-ci.org/internals.html#component-atc) and sitting behind a load balancer.
The **TSA implements CLI over the SSH connection,** supporting [**these commands**](https://concourse-ci.org/internals.html#component-tsa).
### Workers
In order to execute tasks concourse must have some workers. These workers **register themselves** via the [TSA](https://concourse-ci.org/internals.html#component-tsa) and run the services [**Garden**](https://github.com/cloudfoundry-incubator/garden) and [**Baggageclaim**](https://github.com/concourse/baggageclaim).
* **Garden**: This is the **Container Manage AP**I, usually run in **port 7777** via **HTTP**.
* **Baggageclaim**: This is the **Volume Management API**, usually run in **port 7788** via **HTTP**.
<details><summary><strong>Support HackTricks and get benefits!</strong></summary> Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)! Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family) Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com) **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.** **Share your hacking tricks submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.** </details>
