Amazon EC2 Container Service (ECS) II

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Note

Continued from the introductory post (AWS Amazon EC2 Container Service (ECS)), in this post, we'll create a simple app using json file.

Before following this post, we may need to create an ECS cluster and NLB as pre-requisites.

From this post, we'll learn how to create a task definition and a service. Also, we'll see how to make a revision for an existing application.

In the AWS Management Console, on the "Services" menu, click ECS.
In the left navigation pane, click Task Definitions.
Click "Create new Task Definition"
On the Select launch type compatibility page,

EC2

Scroll to the bottom of the screen, then click "Configure via JSON".
This option allows us to load a Task Definition from a configuration file rather than manually creating the definition.
Delete the code in the JSON panel.
The following task definition JSON file specifies two containers that are pulled from the Docker Hub repository.
Copy and paste the following task definition into the JSON panel:

{
  "family": "ECS-demo",
  "containerDefinitions": [
    {
      "volumesFrom": [],
      "portMappings": [
        {
          "hostPort": 80,
          "containerPort": 80
        }
      ],
      "command": null,
      "environment": [],
      "essential": true,
      "entryPoint": null,
      "links": [],
      "mountPoints": [
        {
          "containerPath": "/usr/local/apache2/htdocs",
          "sourceVolume": "my-vol",
          "readOnly": null
        }
      ],
      "memory": 300,
      "name": "simple-app",
      "cpu": 10,
      "image": "httpd:2.4"
    },
    {
      "volumesFrom": [
        {
          "readOnly": null,
          "sourceContainer": "simple-app"
        }
      ],
      "portMappings": [],
      "command": [
        "/bin/sh -c \"while true; do echo '<html> <head> <title>Amazon ECS Sample App</title> <style>body {margin-top: 40px; background-color: #333;} </style> </head><body> <div style=color:white;text-align:center> <h1>Amazon ECS Sample App</h1> <h2>Congratulations!</h2> <p>Your application is now running on a container in Amazon ECS.</p>' > top; /bin/date > date ; echo '</div></body></html>' > bottom; cat top date bottom > /usr/local/apache2/htdocs/index.html ; sleep 1; done\""
      ],
      "environment": [],
      "essential": false,
      "entryPoint": [
        "sh",
        "-c"
      ],
      "links": [],
      "mountPoints": [],
      "memory": 200,
      "name": "busybox",
      "cpu": 10,
      "image": "busybox"
    }
  ],
  "volumes": [
    {
      "host": {
        "sourcePath": null
      },
      "name": "my-vol"
    }
  ]
}

Click "Save".
We will notice that the configuration screen has been populated based upon the template.
Scroll to the bottom of the screen, then click "Create"
This will register the Task Definition in the ECS-demo family.

Create a Service

In this section, we'll create a service definition.

In the left navigation pane, Click Clusters.
In this post, we assume an "ECS-demo-Cluster" has already been created for us (with 3 t2-medium instances).
Click "ECS-demo-Cluster".
On the Services tab, click "Create" then configure:
1. Launch type: EC2
2. Service name: "myService"
3. Number of tasks: "2"
Scroll to the bottom of the screen, then click "Next step"
In the Load balancing section, configure:
1. Load balancer type: Network Load Balancer
2. Service IAM role: ecsServiceRole.
This role allows Amazon ECS to register and deregister container instances on the load balancer as tasks are placed on them.
Click "Add to load balancer" then configure:
1. Producer listener port: 80:TCP
2. Target group name: myTargetGroup

In the Service discover (optional) section, for Namespace select MyPrivateDnsNamespace
Scroll to the bottom of the screen, then click "Next step"
For Set Auto Scaling (optional), click "Next step"

note: actually, an "AutoScaling group" will be created for us, for example, "EC2ContainerService-ECS-demo-Cluster-EcsInstanceAsg" and of course with a "launch configuration", for example, "EC2ContainerService-ECS-demo-Cluster-EcsInstanceLc".
Review our information, then click "Create Service"
Click "View Service", then the details of the service we just created will be displayed.
Click refresh every 30 seconds until the status for each task displays as RUNNING.
Click the Events tab. This shows the progress of the various tasks associated with our service creation request.
Click the Refresh button till we get an event indicating that our service has reached a steady state.
This may take anywhere from 3-5 minutes.
Click Details tab.
In the Details tab, click the Target Group Name. myTargetGroup should be selected.
Click the Targets tab.
In the Targets tab, we can see all of the registered targets.
Click the Description tab.
On the Description tab click our load balancer name.
It should be ECS-demo-LB.
Copy the DNS name of our load balancer to our clipboard.

Open a new browser tab, then paste the load balancer DNS name and press Enter. If everything has been configured correctly we will see the sample app displayed as shown below:

Deploy a New Application Version to the Service

Whenever we update the Docker image of an application, we can create a new task definition with that image and deploy it to our service, one task at a time. The service scheduler creates a task with the new task definition (provided there is an available container instance to place it on), and after it reaches the RUNNING state, a task that is using the old task definition is drained and stopped. This process continues until all of the desired tasks in our service are using the new task definition.

Keep the sample application browser tab open. We will use it again later.
In the AWS Management Console, on the "Services" menu, click ECS.
In the left navigation pane, click Task Definitions.
Select ECS-demo.
Click "Create new revision"
Scroll to the bottom of the screen, then click "Configure via JSON"
Delete the code in the JSON pane.

Copy and paste the code below into the JSON pane:

{
  "family": "ECS-demo",
  "containerDefinitions": [
    {
      "volumesFrom": [],
      "portMappings": [
        {
          "hostPort": 80,
          "containerPort": 80
        }
      ],
      "command": null,
      "environment": [],
      "essential": true,
      "entryPoint": null,
      "links": [],
      "mountPoints": [
        {
          "containerPath": "/usr/local/apache2/htdocs",
          "sourceVolume": "my-vol",
          "readOnly": null
        }
      ],
      "memory": 300,
      "name": "simple-app",
      "cpu": 10,
      "image": "httpd:2.4"
    },
    {
      "volumesFrom": [
        {
          "readOnly": null,
          "sourceContainer": "simple-app"
        }
      ],
      "portMappings": [],
      "command": [
        "/bin/sh -c \"while true; do echo '<html> <head> <title>Amazon ECS Sample App</title> <style>body {margin-top: 40px; background-color: #333;} </style> </head><body> <div style=color:white;text-align:center> <h1>Amazon ECS Sample App</h1> <h2>Thank You!</h2> <p>Your application is now running on a container in Amazon ECS.</p>' > top; /bin/date > date ; echo '</div></body></html>' > bottom; cat top date bottom > /usr/local/apache2/htdocs/index.html ; sleep 1; done\""
      ],
      "environment": [],
      "essential": false,
      "entryPoint": [
        "sh",
        "-c"
      ],
      "links": [],
      "mountPoints": [],
      "memory": 200,
      "name": "busybox",
      "cpu": 10,
      "image": "busybox"
    }
  ],
  "volumes": [
    {
      "host": {
        "sourcePath": null
      },
      "name": "my-vol"
    }
  ]
}

Click "Save"
Click "Create"

This will change the message displayed from Congratulations! to Thank you!.
In the left navigation pane, click Clusters.
Click "ECS-demo-Cluster".
On the Services tab, select "myService".
Click "Update" then configure:
Revision: Select the latest revision

Click "Next Step"
On Step 2, click "Next step"
On Step 3, click "Next step"
Click "Update Service"
Click "View Service", and this will deploy a new version of the application.
Click the Events tab.
Monitor the process of draining connections and stopping tasks.

We can refresh the events by clicking refresh.

We might see the message: service myService was unable to place a task because no container instance met all of its requirements.

Because there are only four instances available this is the expected behavior. The system needs to stop the task on each instance before it can start a new one on each instance.
Continue to refresh occasionally until we see service myService has reached a steady state at the top of the Event list.
Click the Deployments tab. The Running Count should be the same as the Desired count.
Return to our web browser and refresh the Load Balancer's URL (DNS name).
We should see the new version of the app that says Thank You! changed from the previous message, Congratulations!.

Update a Running Service

We can update a running service to change the number of tasks that are maintained by the service or which task definition is used by the tasks. If we have an application that needs more capacity, we can scale-up the service to use more of our container instances (if they are available). If we have unused capacity that we would like to scale-down, we can reduce the number of desired tasks in your service and free up resources.