feat(aws-ecs): expose environment from containerDefinition (#17889)

Closes #17867

* Assigned props.environment to a public readonly member
* Added integration test that confirms the environment can be appended after the task is instantiated

Made 2 cosmetic, but no obvious changes. Environment values are specified:

name: value
name2: value

But in the test and the README.md files the sample values were:

name: something
value: something else

This is using the string 'value" as a key - which, as someone reading the code for the first time, was confusing. So I changed the sample values to more clearly display what's a key and what's a value.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-ecs/README.md

@@ -405,7 +405,7 @@ declare const parameter: ssm.StringParameter;
 declare const taskDefinition: ecs.TaskDefinition;
 declare const s3Bucket: s3.Bucket;
 
-taskDefinition.addContainer('container', {
+const newContainer = taskDefinition.addContainer('container', {
   image: ecs.ContainerImage.fromRegistry("amazon/amazon-ecs-sample"),
   memoryLimitMiB: 1024,
   environment: { // clear text, not for sensitive data
@@ -421,6 +421,7 @@ taskDefinition.addContainer('container', {
     PARAMETER: ecs.Secret.fromSsmParameter(parameter),
   },
 });
+newContainer.addEnvironment('QUEUE_NAME', 'MyQueue');
 ```
 
 The task execution role is automatically granted read permissions on the secrets/parameters. Support for environment

packages/@aws-cdk/aws-ecs/lib/container-definition.ts

@@ -422,6 +422,8 @@ export class ContainerDefinition extends CoreConstruct {
 
   private readonly secrets?: CfnTaskDefinition.SecretProperty[];
 
+  private readonly environment: { [key: string]: string };
+
   /**
    * Constructs a new instance of the ContainerDefinition class.
    */
@@ -457,6 +459,12 @@ export class ContainerDefinition extends CoreConstruct {
       }
     }
 
+    if (props.environment) {
+      this.environment = { ...props.environment };
+    } else {
+      this.environment = {};
+    }
+
     if (props.environmentFiles) {
       this.environmentFiles = [];
 
@@ -547,6 +555,13 @@ export class ContainerDefinition extends CoreConstruct {
     }));
   }
 
+  /**
+   * This method adds an environment variable to the container.
+   */
+  public addEnvironment(name: string, value: string) {
+    this.environment[name] = value;
+  }
+
   /**
    * This method adds one or more resources to the container.
    */
@@ -669,7 +684,7 @@ export class ContainerDefinition extends CoreConstruct {
       volumesFrom: cdk.Lazy.any({ produce: () => this.volumesFrom.map(renderVolumeFrom) }, { omitEmptyArray: true }),
       workingDirectory: this.props.workingDirectory,
       logConfiguration: this.logDriverConfig,
-      environment: this.props.environment && renderKV(this.props.environment, 'name', 'value'),
+      environment: this.environment && Object.keys(this.environment).length ? renderKV(this.environment, 'name', 'value') : undefined,
       environmentFiles: this.environmentFiles && renderEnvironmentFiles(this.environmentFiles),
       secrets: this.secrets,
       extraHosts: this.props.extraHosts && renderKV(this.props.extraHosts, 'hostname', 'ipAddress'),

packages/@aws-cdk/aws-ecs/test/container-definition.test.ts

@@ -690,13 +690,14 @@ describe('container definition', () => {
     const taskDefinition = new ecs.Ec2TaskDefinition(stack, 'TaskDef');
 
     // WHEN
-    taskDefinition.addContainer('cont', {
+    const container = taskDefinition.addContainer('cont', {
       image: ecs.ContainerImage.fromRegistry('test'),
       memoryLimitMiB: 1024,
       environment: {
         TEST_ENVIRONMENT_VARIABLE: 'test environment variable value',
       },
     });
+    container.addEnvironment('SECOND_ENVIRONEMENT_VARIABLE', 'second test value');
 
     // THEN
     expect(stack).toHaveResourceLike('AWS::ECS::TaskDefinition', {
@@ -705,6 +706,37 @@ describe('container definition', () => {
           Environment: [{
             Name: 'TEST_ENVIRONMENT_VARIABLE',
             Value: 'test environment variable value',
+          },
+          {
+            Name: 'SECOND_ENVIRONEMENT_VARIABLE',
+            Value: 'second test value',
+          }],
+        },
+      ],
+    });
+
+
+  });
+
+  test('can add environment variables to container definition with no environment', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const taskDefinition = new ecs.Ec2TaskDefinition(stack, 'TaskDef');
+
+    // WHEN
+    const container = taskDefinition.addContainer('cont', {
+      image: ecs.ContainerImage.fromRegistry('test'),
+      memoryLimitMiB: 1024,
+    });
+    container.addEnvironment('SECOND_ENVIRONEMENT_VARIABLE', 'second test value');
+
+    // THEN
+    expect(stack).toHaveResourceLike('AWS::ECS::TaskDefinition', {
+      ContainerDefinitions: [
+        {
+          Environment: [{
+            Name: 'SECOND_ENVIRONEMENT_VARIABLE',
+            Value: 'second test value',
           }],
         },
       ],