Task definitions in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a task definition in AWS ECS?

A task definition is like a recipe that tells AWS ECS how to run a container. It includes details like which container image to use, how much CPU and memory to give, and what ports to open.

beginner

Name three key parts of a task definition.

1. Container definitions (which containers to run)
2. CPU and memory settings
3. Networking and port mappings

intermediate

Why do you need to register a new task definition revision in ECS?

Because each change to how your container runs (like updating the image or resources) needs a new version. ECS uses these versions to know which setup to use when starting tasks.

beginner

How does a task definition relate to running tasks in ECS?

A task is an instance of a task definition. When you run a task, ECS uses the task definition to know what containers to start and how to configure them.

intermediate

What happens if you update a task definition but don’t update your service to use the new revision?

Your service will keep running tasks with the old task definition version until you tell it to use the new one. So changes won’t take effect automatically.

What does a task definition specify in AWS ECS?

A The user permissions for AWS console

B How to run containers including image, CPU, and ports

C The billing details for ECS usage

D The physical server where containers run

A task definition tells ECS how to run containers, including which image to use, CPU, memory, and ports.

What must you do after changing a task definition to apply updates to a running ECS service?

A Update the service to use the new task definition revision

B Delete the old task definition

C Restart the AWS account

D Nothing, changes apply automatically

You must update the ECS service to use the new task definition revision for changes to take effect.

Which of these is NOT part of a task definition?

A AWS billing plan

B CPU and memory settings

C Network port mappings

D Container image

AWS billing plans are not part of task definitions.

What is a task in ECS?

A A billing invoice

B A user role in AWS

C A physical server

D A running instance of a task definition

A task is a running instance of a task definition in ECS.

Why do task definitions have revisions?

A To increase billing

B To assign user permissions

C To track changes and allow rollback

D To change AWS regions

Revisions track changes to task definitions and allow you to roll back if needed.

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

Think about how you tell ECS what containers to run and how.

Describe the process and reason for updating a task definition revision in ECS.

Consider what happens when you want to change how your app runs.

Practice

1. What is the main purpose of an AWS ECS task definition?

easy

A. To specify how to run a containerized application including resources and settings

B. To create a virtual machine in AWS

C. To store data in AWS S3

D. To manage user permissions in AWS IAM

Solution

1. Step 1: Understand what a task definition is

   A task definition tells AWS ECS how to run your containerized app, including details like CPU, memory, and ports.

2. Step 2: Compare options to the definition

   Only To specify how to run a containerized application including resources and settings correctly describes this purpose. Other options describe unrelated AWS services.

3. Final Answer:

   To specify how to run a containerized application including resources and settings -> Option A

4. Quick Check:

   Task definition = container run instructions [OK]

Hint: Task definitions describe container setup and resources [OK]

Common Mistakes:

• Confusing task definitions with EC2 instances
• Thinking task definitions manage storage or permissions
• Mixing up ECS with other AWS services

2. Which of the following is the correct JSON snippet to define a container image in an ECS task definition?

easy

A. "docker_image": "myrepo/myapp:latest"

B. "image": "myrepo/myapp:latest"

C. "img": "myrepo/myapp:latest"

D. "container_image": "myrepo/myapp:latest"

Solution

1. Step 1: Recall ECS task definition JSON format

   The correct key for specifying the container image is "image" inside the container definitions.

2. Step 2: Check each option's key

   Only "image": "myrepo/myapp:latest" uses the correct key "image". Others use incorrect keys not recognized by ECS.

3. Final Answer:

   "image": "myrepo/myapp:latest" -> Option B

4. Quick Check:

   Container image key = "image" [OK]

Hint: Use "image" key exactly for container images in task definitions [OK]

Common Mistakes:

• Using incorrect keys like "container_image" or "img"
• Confusing task definition keys with Dockerfile syntax
• Misspelling the key name

3. Given this partial ECS task definition snippet:

{
  "containerDefinitions": [{
    "name": "web",
    "image": "nginx",
    "cpu": 256,
    "memory": 512,
    "portMappings": [{"containerPort": 80, "hostPort": 80}]
  }]
}

What will happen when this task runs?

medium

A. The container will use default CPU and memory values ignoring specified ones

B. The task will fail because hostPort cannot be 80

C. The container will run but without port 80 exposed

D. A container named 'web' runs nginx using 256 CPU units and 512 MB memory, exposing port 80

Solution

1. Step 1: Analyze container resource settings

   The task defines CPU as 256 units and memory as 512 MB, which are valid resource allocations.

2. Step 2: Check port mapping

   Port 80 is mapped from container to host, so port 80 is exposed correctly.

3. Final Answer:

   A container named 'web' runs nginx using 256 CPU units and 512 MB memory, exposing port 80 -> Option D

4. Quick Check:

   Resources and ports set correctly = runs as expected [OK]

Hint: Port mappings expose container ports to host ports directly [OK]

Common Mistakes:

• Assuming hostPort 80 is invalid (it is allowed)
• Ignoring resource settings and thinking defaults apply
• Missing port exposure due to misunderstanding portMappings

4. You have this ECS task definition snippet:

{
  "containerDefinitions": [{
    "name": "app",
    "image": "myapp:latest",
    "cpu": 512,
    "memory": 1024
  }]
}

When you try to run this task, it fails with an error about missing port mappings. What is the likely fix?

medium

A. Add a portMappings section specifying containerPort and hostPort

B. Remove the cpu and memory fields

C. Change the image name to include a registry URL

D. Rename the container from 'app' to 'web'

Solution

1. Step 1: Understand the error about missing port mappings

   If the app requires network access, port mappings must be defined to expose ports.

2. Step 2: Identify the fix

   Adding a portMappings section with containerPort and hostPort will resolve the error by exposing the needed ports.

3. Final Answer:

   Add a portMappings section specifying containerPort and hostPort -> Option A

4. Quick Check:

   Missing ports error = add portMappings [OK]

Hint: Add portMappings to expose container ports when needed [OK]

Common Mistakes:

• Removing CPU or memory which are unrelated to port errors
• Changing image name unnecessarily
• Renaming container without fixing ports

5. You want to update your ECS service to run a new version of your app with environment variables and increased memory. Which part of the task definition should you modify?

hard

A. Change the taskRoleArn to a new IAM role

B. Modify the family name of the task definition

C. Update the containerDefinitions section to include new environment variables and increase the memory value

D. Add a new volume definition without changing container settings

Solution

1. Step 1: Identify where environment variables and memory are set

   Environment variables and memory limits are set inside the containerDefinitions section of the task definition.

2. Step 2: Understand the update process

   To update the app version and resources, modify containerDefinitions with new environment variables and increased memory.

3. Final Answer:

   Update the containerDefinitions section to include new environment variables and increase the memory value -> Option C

4. Quick Check:

   Env vars and memory updated in containerDefinitions [OK]

Hint: Change containerDefinitions to update app settings and resources [OK]

Common Mistakes:

• Changing taskRoleArn which controls permissions, not env or memory
• Modifying family name which identifies task definition versions
• Adding volumes without updating container environment or memory