Bird
Raised Fist0
AWScloud~5 mins

Services and tasks in AWS - Commands & Configuration

Choose your learning style10 modes available
LearnWhyDeepVisualTryChallengeProjectRecallTime
Introduction
When you want to run and manage containers on AWS, you use services and tasks. A service keeps your containers running and replaces them if they stop. A task is a single running container or group of containers based on a task definition.
When you want to run a web app in containers and keep it always available.
When you need to update your app without downtime by replacing old containers with new ones.
When you want to run batch jobs or one-time container tasks on AWS.
When you want to control how many copies of your app run at the same time.
When you want AWS to automatically restart containers if they fail.
Config File - task-definition.json
task-definition.json
{
  "family": "my-app-task",
  "networkMode": "awsvpc",
  "containerDefinitions": [
    {
      "name": "my-app-container",
      "image": "nginx:1.23",
      "portMappings": [
        {
          "containerPort": 80,
          "protocol": "tcp"
        }
      ],
      "essential": true
    }
  ],
  "requiresCompatibilities": ["FARGATE"],
  "cpu": "256",
  "memory": "512"
}

This JSON file defines a task for AWS ECS. The family names the task. networkMode sets networking to AWS VPC mode. containerDefinitions describes the container to run, here an nginx web server on port 80. requiresCompatibilities specifies it runs on Fargate, a serverless container service. cpu and memory set resource limits.

Commands
This command registers the task definition with AWS ECS so you can use it to run containers.
Terminal
aws ecs register-task-definition --cli-input-json file://task-definition.json
Expected OutputExpected
{ "taskDefinition": { "taskDefinitionArn": "arn:aws:ecs:us-east-1:123456789012:task-definition/my-app-task:1", "family": "my-app-task", "revision": 1, "status": "ACTIVE", "requiresAttributes": [ { "name": "com.amazonaws.ecs.capability.ecr-auth" }, { "name": "ecs.capability.execution-role-awslogs" } ], "containerDefinitions": [ { "name": "my-app-container", "image": "nginx:1.23", "cpu": 0, "memory": null, "portMappings": [ { "containerPort": 80, "protocol": "tcp" } ], "essential": true } ], "requiresCompatibilities": [ "FARGATE" ], "cpu": "256", "memory": "512" } }
→
--cli-input-json - Specifies the JSON file with the task definition details
This command creates a service that runs one copy of the task on Fargate in the specified subnet with a public IP.
Terminal
aws ecs create-service --cluster default --service-name my-app-service --task-definition my-app-task --desired-count 1 --launch-type FARGATE --network-configuration "awsvpcConfiguration={subnets=[subnet-0abc1234],assignPublicIp=ENABLED}"
Expected OutputExpected
{ "service": { "serviceName": "my-app-service", "clusterArn": "arn:aws:ecs:us-east-1:123456789012:cluster/default", "status": "ACTIVE", "desiredCount": 1, "runningCount": 0, "pendingCount": 1, "launchType": "FARGATE", "taskDefinition": "my-app-task:1" } }
→
--desired-count - Sets how many task copies to run
→
--launch-type - Specifies to use Fargate serverless containers
→
--network-configuration - Defines networking details like subnet and public IP
This command lists the running tasks for the service to check if the container started.
Terminal
aws ecs list-tasks --cluster default --service-name my-app-service
Expected OutputExpected
{ "taskArns": [ "arn:aws:ecs:us-east-1:123456789012:task/default/abcdef1234567890" ] }
This command shows detailed information about the running task, including status and container details.
Terminal
aws ecs describe-tasks --cluster default --tasks arn:aws:ecs:us-east-1:123456789012:task/default/abcdef1234567890
Expected OutputExpected
{ "tasks": [ { "taskArn": "arn:aws:ecs:us-east-1:123456789012:task/default/abcdef1234567890", "lastStatus": "RUNNING", "desiredStatus": "RUNNING", "containers": [ { "name": "my-app-container", "lastStatus": "RUNNING", "networkBindings": [ { "bindIP": "0.0.0.0", "containerPort": 80, "hostPort": 80 } ] } ] } ] }
Key Concept

A service keeps your containers running and replaces them if they stop, while a task is a single running container or group of containers based on a task definition.

Common Mistakes
Not specifying the correct subnet in the network configuration when creating the service.
The task will fail to start because it has no network to connect to.
Always specify a valid subnet ID in the --network-configuration flag.
Forgetting to register the task definition before creating the service.
The service cannot find the task definition and will not start any tasks.
Run aws ecs register-task-definition first with a valid JSON file.
Setting desired-count to zero when creating the service.
No tasks will run, so your app will not be available.
Set desired-count to at least 1 to run one or more task copies.
Summary
Register a task definition JSON file to tell AWS what containers to run and how.
Create a service to run and maintain the desired number of task copies on Fargate.
Use list-tasks and describe-tasks commands to check the status and details of running containers.

Practice

(1/5)
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
Recommended

Ready to prove it?

Pass the test and this pattern moves unknown strong while earning +1 Grip toward your certificate.

10 questions~5 mineasy hard