Services and tasks in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an AWS service?

An AWS service is a ready-made cloud tool or feature provided by Amazon Web Services to help you build, store, or manage your applications and data.

beginner

What is a task in AWS ECS (Elastic Container Service)?

A task is a running instance of a container or group of containers defined by a task definition in AWS ECS. It represents the actual work being done.

intermediate

How do AWS services and tasks relate in ECS?

An ECS service manages and runs one or more tasks continuously to keep your application available and scalable.

intermediate

Why use an ECS service instead of running tasks manually?

Because ECS services automatically restart tasks if they fail and balance the load, making your app more reliable without manual work.

beginner

What is a task definition in ECS?

A task definition is like a recipe that tells ECS what containers to run, what resources they need, and how they should behave.

What does an ECS service do?

A Runs and maintains tasks automatically

B Stores data in the cloud

C Creates virtual machines

D Manages user permissions

An ECS service runs and keeps tasks running to ensure your app stays available.

What is a task in AWS ECS?

A A running container or group of containers

B A storage bucket

C A virtual server

D A user account

A task is the actual running container(s) doing the work in ECS.

Which AWS service helps you run containers without managing servers?

A Amazon RDS

B Amazon S3

C Amazon ECS

D AWS IAM

Amazon ECS lets you run containers easily without managing servers.

What is a task definition used for in ECS?

A To store files

B To define how containers run and their settings

C To create user roles

D To monitor network traffic

Task definitions tell ECS what containers to run and how.

Why is using an ECS service better than running tasks manually?

A It creates virtual machines

B It costs less money

C It stores data permanently

D It automatically restarts tasks and balances load

ECS services keep tasks running and manage load without manual effort.

Explain the relationship between AWS ECS services and tasks.

Think about how a manager (service) keeps workers (tasks) working.

Describe what a task definition is and why it is important in ECS.

Imagine a recipe that tells you how to cook a dish.

Practice

1. What is the main role of a service in AWS when managing your app tasks?

easy

A. To define the resources and containers for the app

B. To keep the app tasks running and replace them if they fail

C. To store data for the app

D. To monitor network traffic

Solution

1. Step 1: Understand what a service does

   A service manages running copies of your app tasks and ensures they stay running.

2. Step 2: Compare with other options

   Defining resources and containers is the task's role, not the service's. Storing data and monitoring traffic are unrelated.

3. Final Answer:

   To keep the app tasks running and replace them if they fail -> Option B

4. Quick Check:

   Service manages tasks = B [OK]

Hint: Services keep tasks running and replace failed ones [OK]

Common Mistakes:

• Confusing service with task definition
• Thinking service stores data
• Assuming service monitors network

2. Which of the following is the correct way to define a task in AWS ECS?

easy

A. A database schema for app data

B. A YAML file listing EC2 instances

C. A JSON file specifying containers, CPU, and memory

D. A script to launch EC2 instances

Solution

1. Step 1: Identify task definition format

   A task in AWS ECS is defined by a JSON file that specifies containers, CPU, and memory requirements.

2. Step 2: Eliminate incorrect options

   YAML listing EC2 instances is not a task definition. Scripts to launch EC2 or database schemas are unrelated.

3. Final Answer:

   A JSON file specifying containers, CPU, and memory -> Option C

4. Quick Check:

   Task definition = JSON file with containers [OK]

Hint: Task definitions use JSON to specify containers and resources [OK]

Common Mistakes:

• Confusing task definition with instance listing
• Using scripts instead of JSON for tasks
• Mixing database schemas with task definitions

3. If you create a service with a desired count of 3 tasks, but one task fails, what will AWS ECS do?

medium

A. Replace the failed task to maintain 3 running tasks

B. Stop all tasks and alert the user

C. Ignore the failure and keep 2 tasks running

D. Scale down the service to 2 tasks

Solution

1. Step 1: Understand service desired count behavior

   The service tries to keep the number of running tasks equal to the desired count.

2. Step 2: What happens on task failure?

   If a task fails, the service replaces it to maintain the desired count of 3 tasks.

3. Final Answer:

   Replace the failed task to maintain 3 running tasks -> Option A

4. Quick Check:

   Service maintains desired count = A [OK]

Hint: Service replaces failed tasks to keep desired count [OK]

Common Mistakes:

• Thinking service stops all tasks on failure
• Assuming service ignores failures
• Believing service scales down automatically

4. You defined a task with 512 MB memory but your service fails to start tasks due to insufficient resources. What is the likely problem?

medium

A. The container image is missing

B. The task definition JSON is invalid

C. The service desired count is set to zero

D. The cluster has no available memory to run the task

Solution

1. Step 1: Analyze the error cause

   Insufficient resources usually mean the cluster lacks enough memory to run the task.

2. Step 2: Check other options

   Invalid JSON or zero desired count would cause different errors. Missing image causes container start failure, not resource error.

3. Final Answer:

   The cluster has no available memory to run the task -> Option D

4. Quick Check:

   Insufficient resources = cluster memory shortage [OK]

Hint: Check cluster memory before blaming task definition [OK]

Common Mistakes:

• Assuming JSON syntax error causes resource failure
• Ignoring cluster resource limits
• Confusing desired count zero with resource shortage

5. You want to run a web app that scales automatically based on CPU usage. Which combination should you use in AWS ECS?

hard

A. Create a service with a task definition and enable auto scaling on the service

B. Create only tasks without a service and manually start more tasks

C. Use EC2 instances without ECS to run containers

D. Create a service but disable task definitions

Solution

1. Step 1: Identify components for scaling

   A service manages tasks and can be configured with auto scaling based on CPU.

2. Step 2: Evaluate other options

   Running tasks without a service lacks auto scaling. Using EC2 alone misses ECS benefits. Disabling task definitions is invalid.

3. Final Answer:

   Create a service with a task definition and enable auto scaling on the service -> Option A

4. Quick Check:

   Service + task + auto scaling = C [OK]

Hint: Use service with auto scaling for CPU-based scaling [OK]

Common Mistakes:

• Skipping service and expecting auto scaling
• Confusing EC2 usage without ECS
• Disabling task definitions breaks deployment