# Server Workers - Uvicorn with Workers Let's check back those deployment concepts from before: * Security - HTTPS * Running on startup * Restarts * **Replication (the number of processes running)** * Memory * Previous steps before starting Up to this point, with all the tutorials in the docs, you have probably been running a **server program**, for example, using the `fastapi` command, that runs Uvicorn, running a **single process**. When deploying applications you will probably want to have some **replication of processes** to take advantage of **multiple cores** and to be able to handle more requests. As you saw in the previous chapter about [Deployment Concepts](concepts.md){.internal-link target=_blank}, there are multiple strategies you can use. Here I'll show you how to use **Uvicorn** with **worker processes** using the `fastapi` command or the `uvicorn` command directly. /// info If you are using containers, for example with Docker or Kubernetes, I'll tell you more about that in the next chapter: [FastAPI in Containers - Docker](docker.md){.internal-link target=_blank}. In particular, when running on **Kubernetes** you will probably **not** want to use workers and instead run **a single Uvicorn process per container**, but I'll tell you about it later in that chapter. /// ## Multiple Workers You can start multiple workers with the `--workers` command line option: //// tab | `fastapi` If you use the `fastapi` command:
```console $ 
 fastapi run --workers 4 main.py
INFO     Using path main.py
INFO     Resolved absolute path /home/user/code/awesomeapp/main.py
INFO     Searching for package file structure from directories with __init__.py files
INFO     Importing from /home/user/code/awesomeapp

 ╭─ Python module file ─╮
 │                      │
 │  🐍 main.py          │
 │                      │
 ╰──────────────────────╯

INFO     Importing module main
INFO     Found importable FastAPI app

 ╭─ Importable FastAPI app ─╮
 │                          │
 │  from main import app    │
 │                          │
 ╰──────────────────────────╯

INFO     Using import string main:app

 ╭─────────── FastAPI CLI - Production mode ───────────╮
 │                                                     │
 │  Serving at: http://0.0.0.0:8000                    │
 │                                                     │
 │  API docs: http://0.0.0.0:8000/docs                 │
 │                                                     │
 │  Running in production mode, for development use:   │
 │                                                     │
 │  fastapi dev                                        │
 │                                                     │
 ╰─────────────────────────────────────────────────────╯

INFO:     Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)
INFO:     Started parent process [27365]
INFO:     Started server process [27368]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Started server process [27369]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Started server process [27370]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Started server process [27367]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
```
//// //// tab | `uvicorn` If you prefer to use the `uvicorn` command directly:
```console $ uvicorn main:app --host 0.0.0.0 --port 8080 --workers 4 INFO: Uvicorn running on http://0.0.0.0:8080 (Press CTRL+C to quit) INFO: Started parent process [27365] INFO: Started server process [27368] INFO: Waiting for application startup. INFO: Application startup complete. INFO: Started server process [27369] INFO: Waiting for application startup. INFO: Application startup complete. INFO: Started server process [27370] INFO: Waiting for application startup. INFO: Application startup complete. INFO: Started server process [27367] INFO: Waiting for application startup. INFO: Application startup complete. ```
//// The only new option here is `--workers` telling Uvicorn to start 4 worker processes. You can also see that it shows the **PID** of each process, `27365` for the parent process (this is the **process manager**) and one for each worker process: `27368`, `27369`, `27370`, and `27367`. ## Deployment Concepts Here you saw how to use multiple **workers** to **parallelize** the execution of the application, take advantage of **multiple cores** in the CPU, and be able to serve **more requests**. From the list of deployment concepts from above, using workers would mainly help with the **replication** part, and a little bit with the **restarts**, but you still need to take care of the others: * **Security - HTTPS** * **Running on startup** * ***Restarts*** * Replication (the number of processes running) * **Memory** * **Previous steps before starting** ## Containers and Docker In the next chapter about [FastAPI in Containers - Docker](docker.md){.internal-link target=_blank} I'll explain some strategies you could use to handle the other **deployment concepts**. I'll show you how to **build your own image from scratch** to run a single Uvicorn process. It is a simple process and is probably what you would want to do when using a distributed container management system like **Kubernetes**. ## Recap You can use multiple worker processes with the `--workers` CLI option with the `fastapi` or `uvicorn` commands to take advantage of **multi-core CPUs**, to run **multiple processes in parallel**. You could use these tools and ideas if you are setting up **your own deployment system** while taking care of the other deployment concepts yourself. Check out the next chapter to learn about **FastAPI** with containers (e.g. Docker and Kubernetes). You will see that those tools have simple ways to solve the other **deployment concepts** as well. ✨