ECS Fargate Tutorial with FastAPI

In this article we are going to talk about what ECS is and present you a tutorial on how to deploy an API built using Python’s FastAPI framework and packaged in a Docker image. We assume you have previous knowledge of Python and Docker to follow it through.

What is ECS

Amazon Elastic Container Service (ECS) is a container management service that offers orchestration, service discovery, serverless deployment, and more for your containerized applications.

If you’re looking for a more thorough ECS Overview Video, check out my article here.

ECS Key Concepts

In summary, ECS is about configuring services to maintain and scale tasks defined by task definitions running on a cluster. Tasks may run on two different launch types. The first is a serverless manner called Fargate, and the other is traditional EC2 instances.

Task Definition

Task definitions are the configurations of a group of 1 up to 10 containers that will run together once initialized. These containers can be short or long-lived.

In a task definition, you choose how much of the instances resources you are going to allocate and how much each container may consume of these pre-allocated resources. Aside from each container’s resources you also configure things like the images to be used, the ports to open, the environment variables, etc.


A task is the instantiation of a task definition within a cluster.


Your tasks and services run on infrastructure that is registered to a cluster. Clusters are used to separate groups of services and/or independent tasks from each other in a given region. Clusters support both launch types simultaneously.


Fargate is a serverless option for running containers. Fargate instances are managed by AWS and may run only one task at a time. These instances may be configured with as little as .25 vCPU and 512MB of RAM up to 16 vCPU and 120GB of RAM with storage ranging from 20 to 200GB. The RAM must always match 2x to 8x the vCPU configuration.

EC2 Container Instance

ECS container instances are EC2 machines running an ECS-optimized AMI. They are configured to run tasks of a particular ECS cluster. These instances can run as many tasks as their resources can handle.


You can write a task definition that allocates 4 vCPU and 8GB of RAM and has 3 containers C1, C2 and C3, where C1 and C2 get 1vCPU and 2GB of RAM each and C3 gets 2 vCPU and 4GB of RAM. Now, imagine an EC2 instance with 8 vCPU and 16GB of RAM. Not considering the resources used by the OS, you could run 2 tasks defined by this task definition. Note that if you are using Fargate, you have to instantiate two machines, one for each task. The resources will be provisioned automatically according to the task definition.

Application Types

Standalone Task

A standalone task is a task that you start manually or programmatically. They are ideally short-lived and stop after finishing their execution. It is recommended fork workloads such as batch jobs.


As opposed to a standalone task, a service enables you to maintain a specified number of tasks running in a cluster. If for any reason, a task fails, the service automatically instantiates another one for you to replace it. Services are the recommended way to run web applications, for example.

Some other features are comprised by services, such as:

What is ECR

Amazon Elastic Container Registry (ECR) is AWS’ implementation of the Open Container Initiative (OCI) Distribution Specification. OCI suggests a “build, ship, run” philosophy for dealing with packaging and delivery of containerized applications. What it means is, you build an image, ship it somewhere and retrieve it when you need to run a container. The place where you ship your images to retrieve it from is called a registry, such as ECR.

How ECS uses ECR

When you define an image to be used in a Task Definition, you specify an image URI that will point to a container registry where ECS will fetch the image from when initializing a task. When using AWS ECS, you can benefit from better performance and less cost by using ECR to store your images.


Part 1 – Application

For our application we are going to use the FastAPI’s guide on how to deploy the framework as a reference, with some minor changes. The complete guide with recomendations can be found at

├── app
│   ├──
│   └──
├── Dockerfile
└── requirements.txt
from fastapi import FastAPI
from typing import Union

app = FastAPI()

def read_root():
    return {"Hello": "World"}

def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}

This code defines two callable routes when the API is running. One in / and another in /items/{id}. Both routes respond to the HTTP method GET only.

FROM python:3.10-slim


COPY ./requirements.txt /code/requirements.txt

RUN pip install --no-cache-dir --upgrade -r /code/requirements.txt

COPY ./app /code/app

CMD ["uvicorn", "app.main:app", "--host", "", "--port", "80"]

When an image is built using this definition, it starts by fetching the python:3.10-slim base image from the docker public registry. Then, copies the requirements.txt file and install the requirements using pip. Finally, it copies the app folder. When a container starts it runs the uvicorn ASGI webserver using the app defined in

Part 2 – ECR

To follow this part make sure you have Docker and the AWS CLI installed. To know how to install and configure them refer to [link] and [link], respectively.

You can create a new ECR repository using the AWS CLI by running the command:

aws ecr create-repository --repository-name <repository_name>

or by using the console as shown below.

aws ecr get-login-password --region <region> | docker login --username AWS --password-stdin <aws account id>.dkr.ecr.<region>

This is the command 1 you’ve saved on the previous step. You should see the output below.

to push the image to the repository. This is command 4.

Part 3 – ECS

Task Role

The task role is the permissions your containers will have when a task is running. You might need to download something from S3 during runtime. This is the role you should configure with permissions to do so. Task Execution Role

Task Execution Role

The Task Executions role is the permissions the container agent that fetches your images and setup your environment will have when starting tasks. You might permissions such as fetching secrets or parameters from secrets manager or the paramter store to set as environment variables, for example. This is the role you should configure with permissions to do so.

Part 4 – Run a Standalone Task

Step 4.1 – Configure the task:

Step 4.2 – Verify if the task started:

Step 4.3 – Test the API:

Part 5 – Create a Service

Overall, AWS ECS and ECR are powerful tools that can help you to deploy, manage and scale your containerized applications. They provide a way to automate the management of clusters and resources, as well as a way to store and distribute your container images in a private and secure way. With the knowledge gained in this article, you are ready to build and deploy your own applications using these services on AWS.

  1. If you are using Fargate, you have to instantiate two machines, one for each task. The resources will be provisioned automatically according to the task definition. ↩︎
  2. You can find this button by clicking in the repository name if you missed the notification. ↩︎
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