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ECS Task Definitions

This document provides a comprehensive overview of the task-definition.ts file, which defines Amazon ECS (Elastic Container Service) task definitions for various components of the Ghost application infrastructure.

Table of Contents​

  1. Overview
  2. Imports and Configuration
  3. IAM Roles
  4. Task Definitions
  5. CloudWatch Log Group

Overview​

This TypeScript file uses Pulumi to define ECS task definitions for different components of the Ghost application, including:

  • Web Application
  • Celery Worker
  • Celery Scheduler
  • Flower (Celery monitoring tool)
  • pgAdmin (PostgreSQL administration tool)

Each task definition includes specific configurations for CPU, memory, network mode, IAM roles, and container definitions.

Imports and Configuration​

import * as aws from "@pulumi/aws";
import * as pulumi from "@pulumi/pulumi";
import { pgAdminConfig, environmentVariables, image, flowerConfig, appConfig } from "./config";

The file imports necessary modules from Pulumi and AWS SDKs, as well as configuration variables from a local config file.

const stack = pulumi.getStack();
const region = process.env.REGION || "use2";

It also sets up variables for the current stack and region.

IAM Roles​

A helper function createIAMRoles is defined to create IAM roles for ECS tasks:

const createIAMRoles = (name: string) => {
  // ... (role creation logic)
};

This function creates two roles for each task:

  1. Execution Role: Allows ECS to pull container images and publish logs to Amazon CloudWatch on your behalf.
  2. Task Role: Grants permissions to the task itself, allowing it to access AWS services.

The following policies are attached to the task role:

  • AmazonSSMManagedInstanceCore
  • CloudWatchLogsFullAccess
  • AmazonS3FullAccess

note refer to Iam-roles for more details about the policies attached to the task role

Task Definitions​

Web Application​

const webappRole = createIAMRoles("webapp");
export const webappTaskDefinition = new aws.ecs.TaskDefinition(`webapp-task-${stack}`, {
  // ... (task definition properties)
});

Key features:

  • Uses 512 CPU units and 1024 MB of memory
  • Runs on Fargate
  • Exposes port 8080
  • Uses a custom entry point script
  • Logs to CloudWatch

Celery Worker​

const celeryWorkerRole = createIAMRoles("celeryworker");
export const celeryWorkerTaskDefinition = new aws.ecs.TaskDefinition(`celeryworker-${stack}-ecs-${region}-task`, {
  // ... (task definition properties)
});

Key features:

  • Uses 256 CPU units and 512 MB of memory
  • Runs the Celery worker process
  • Logs to CloudWatch

Celery Scheduler​

const celerySchedulerRole = createIAMRoles("celeryscheduler");
export const celerySchedulerTaskDefinition = new aws.ecs.TaskDefinition(`celeryscheduler-${stack}-ecs-${region}-task`, {
  // ... (task definition properties)
});

Key features:

  • Uses 256 CPU units and 512 MB of memory
  • Runs the Celery scheduler with Django Celery Beat
  • Logs to CloudWatch

Flower​

const flowerRole = createIAMRoles("flower");
export const flowerTaskDefinition = new aws.ecs.TaskDefinition(`flower-${stack}-ecs-${region}-task`, {
  // ... (task definition properties)
});

Key features:

  • Uses 256 CPU units and 512 MB of memory
  • Runs the Flower monitoring tool for Celery
  • Exposes port 5555
  • Configures basic authentication
  • Logs to CloudWatch

pgAdmin​

const pgAdminRole = createIAMRoles("pgadmin");
export const pgAdminTaskDefinition = new aws.ecs.TaskDefinition(`pgadmin-${stack}-ecs-${region}-task`, {
  // ... (task definition properties)
});

Key features:

  • Uses 256 CPU units and 512 MB of memory
  • Runs pgAdmin 4 for PostgreSQL management
  • Exposes port 80
  • Configures default email and password
  • Logs to CloudWatch

CloudWatch Log Group​

export const logGroup = new aws.cloudwatch.LogGroup(`gh-webapp-${stack}-cw-${region}-log-group`, {
  name: `gh-webapp-${stack}-cw-${region}-log-group`,
  retentionInDays: 30,
});

A CloudWatch Log Group is created to store logs from all the ECS tasks. Logs are retained for 30 days.