Services and tasks in AWS - Step-by-Step Execution

Process Flow - Services and tasks

Create Task Definition

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Register Task Definition

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Create Service

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Service Launches Tasks

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Tasks Run Containers

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Monitor & Scale Tasks

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Update Service

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Replace Tasks

This flow shows how you define a task, register it, create a service to run tasks, and how the service manages running and updating tasks.

Execution Sample

AWS

1. Define task with container info
2. Register task definition
3. Create service with task definition
4. Service launches tasks
5. Tasks run containers

This sequence shows how AWS ECS runs containers by defining tasks and services.

Process Table

Step	Action	Input	Result	Notes
1	Define Task	Container image: nginx	Task Definition created	Defines container and resources
2	Register Task	Task Definition JSON	Task Definition ARN	Task is saved and versioned
3	Create Service	Task Definition ARN, desired count=2	Service created	Service manages tasks
4	Service Launches Tasks	Desired count=2	2 Tasks started	Tasks run containers
5	Tasks Running	Container image nginx	Containers running	Containers serve traffic
6	Monitor & Scale	CPU usage high	Service scales to 3 tasks	More tasks launched
7	Update Service	New Task Definition version	Service updates tasks	Old tasks replaced
8	Tasks Replaced	Old tasks stopped	New tasks running	Service stable with new version
9	Exit	Desired count met	Stable service	No further action needed

💡 Service reaches desired count and tasks run containers successfully

Status Tracker

Variable	Start	After Step 3	After Step 4	After Step 6	After Step 8	Final
Task Definition	None	Registered v1	Registered v1	Registered v1	Registered v2	Registered v2
Service Desired Count	0	2	2	3	3	3
Running Tasks	0	0	2	3	3	3
Task Version	None	v1	v1	v1	v2	v2

Key Moments - 3 Insights

Why does the service launch multiple tasks instead of just one?

Because the service's desired count is set to more than one (2 in step 3), so it launches that many tasks to run containers (see execution_table step 4).

What happens when the service updates to a new task definition version?

The service replaces old tasks with new tasks running the updated version (see execution_table steps 7 and 8). This ensures smooth updates without downtime.

How does the service decide to scale up the number of tasks?

It monitors metrics like CPU usage and scales tasks up or down to meet demand (see execution_table step 6).

Visual Quiz - 3 Questions

Look at the execution table, how many tasks does the service launch initially?

A 1

B 2

C 3

D 0

💡 Hint

Check step 4 in the execution_table where the service launches tasks.

At which step does the service update to a new task definition version?

A Step 5

B Step 6

C Step 7

D Step 8

💡 Hint

Look for the step labeled 'Update Service' in the execution_table.

If the desired count changes from 2 to 3, what happens in the execution table?

A Service scales to 3 tasks

B Service deletes task definitions

C Service stops tasks

D No change

💡 Hint

See step 6 where the service scales tasks based on CPU usage.

Concept Snapshot

AWS ECS runs containers using tasks and services.
Define a task with container info.
Register task definition to save it.
Create a service to run tasks.
Service launches and manages tasks.
Update service to replace tasks with new versions.

Full Transcript

This visual execution shows how AWS ECS uses tasks and services to run containers. First, you define a task with container details like the image. Then you register this task definition, which saves it with a version. Next, you create a service that uses this task definition and sets how many tasks to run. The service launches the tasks, which run containers. The service monitors the tasks and can scale them up or down based on demand. When you update the task definition, the service replaces old tasks with new ones running the updated version. This process ensures your containers run reliably and can be updated smoothly.