Merge pull request awsdocs#124 from hacker65536/fixContext

Fix and add example code to Context
eladb · Sep 24, 2019 · d8f2ec9 · d8f2ec9
2 parents edd18b8 + 656c2f7
commit d8f2ec9
Showing 1 changed file with 84 additions and 19 deletions.
diff --git a/doc_source/context.md b/doc_source/context.md
@@ -5,9 +5,10 @@ The AWS CDK uses context to retrieve information such as the Availability Zones
 ## Construct Context<a name="context_construct"></a>
 
 You can provide context values in three different ways:
-+ Automatically by the AWS CDK CLI after required information, such as the list of Availability Zones, is looked up from the current AWS account\.
-+ Provided by the user through the CLI using the \-\-context option, or in the `context` key of the `cdk.json` file\.
-+ Set in code using the `construct.node.setContext` method\.
+
+- Automatically by the AWS CDK CLI after required information, such as the list of Availability Zones, is looked up from the current AWS account\.
+- Provided by the user through the CLI using the \-\-context option, or in the `context` key of the `cdk.json` file\.
+- Set in code using the `construct.node.setContext` method\.
 
 Context entries are scoped to the construct that created them: they are visible to children constructs, but not to siblings\. Context entries that are set by the CLI, either automatically or from the \-\-context option, are implicitly set on the `App` construct, and are visible to the app\.
 
@@ -19,16 +20,16 @@ The AWS CDK supports several context methods that enable AWS CDK apps to get con
 
 The following are the context methods:
 
-[HostedZone\.fromLookup](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-route53.HostedZone.html#static-from-lookupscope-id-query)  
+[HostedZone\.fromLookup](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-route53.HostedZone.html#static-from-wbr-lookupscope-id-query)  
 Gets the hosted zones in your account\.
 
 [stack\.availabilityZones](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_core.Stack.html#availabilityzones)  
 Gets the supported Availability Zones\.
 
-StringParameter\.valueFromLookup  
+[StringParameter\.valueFromLookup](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-ssm.StringParameter.html#static-value-wbr-from-wbr-lookupscope-parametername)  
 Gets a value from the current Region's AWS Systems Manager Parameter Store\.
 
-Vpc\.fromLookup  
+[Vpc\.fromLookup](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-ec2.Vpc.html#static-from-wbr-lookupscope-id-options)  
 Gets the existing VPCs in your accounts\.
 
 If a given context information isn't available, the AWS CDK app notifies the AWS CDK CLI that the context information is missing\. The CLI then queries the current AWS account for the information, stores the resulting context information in the `cdk.context.json` file, and executes the AWS CDK app again with the context values\.
@@ -41,14 +42,14 @@ Use the cdk context command to view and manage the information in your `cdk.cont
 
 ```
 Context found in cdk.json:
-      
-┌───────────────────────────────────────────────────────────────────────────|
-│ # | Key                                                         │ Value                                                        |
-├───────────────────────────────────────────────────────────────────────────|
-│ 1 | availability-zones:account=123456789012:region=eu-central-1 │ [ "eu-central-1a", "eu-central-1b", "eu-central-1c" ]        |
-├───────────────────────────────────────────────────────────────────────────|
-│ 2 | availability-zones:account=123456789012:region=eu-west-1    │ [ "eu-west-1a", "eu-west-1b", "eu-west-1c" ]                 |
-└───────────────────────────────────────────────────────────────────────────|
+
+┌───┬─────────────────────────────────────────────────────────────┬──────────────────────────────────────────────────────────────┐
+│ # | Key                                                         │ Value                                                        │
+├───┼─────────────────────────────────────────────────────────────┼──────────────────────────────────────────────────────────────│
+│ 1 | availability-zones:account=123456789012:region=eu-central-1 │ [ "eu-central-1a", "eu-central-1b", "eu-central-1c" ]        │
+├───┼─────────────────────────────────────────────────────────────┼──────────────────────────────────────────────────────────────│
+│ 2 | availability-zones:account=123456789012:region=eu-west-1    │ [ "eu-west-1a", "eu-west-1b", "eu-west-1c" ]                 │
+└───┴─────────────────────────────────────────────────────────────┴──────────────────────────────────────────────────────────────┘
 
 Run cdk context --reset KEY_OR_NUMBER to remove a context key. It will be refreshed on the next CDK synthesis run.
 ```
@@ -68,15 +69,79 @@ reset. It will be refreshed on the next SDK synthesis run.
 Therefore, if you want to update to the latest version of the Amazon Linux AMI, you can use the preceding example to do a controlled update of the context value and reset it, and then synthesize and deploy your app again\.
 
 ```
-cdk synth
+$ cdk synth
 ```
 
+To clear all of the stored context values for your app, run cdk context \-\-clear, as follows\.
+
 ```
-...
+$ cdk context --clear
 ```
 
-To clear all of the stored context values for your app, run cdk context \-\-clear, as follows\.
+The following is an example of importing an existing vpc using cdk context.
+
+```
+import cdk = require('@aws-cdk/core');
+import ec2 = require('@aws-cdk/aws-ec2');
+
+export class ExistsvpcStack extends cdk.Stack {
+  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
+    super(scope, id, props);
+
+    const vpcid = this.node.tryGetContext('vpcid');
 
+    const vpc = ec2.Vpc.fromLookup(this, 'VPC', {
+      vpcId: vpcid,
+    });
+
+    const pubsubnets = vpc.selectSubnets({subnetType: ec2.SubnetType.PUBLIC});
+
+    new cdk.CfnOutput(this, 'publicsubnets', {
+      value: pubsubnets.subnetIds.toString(),
+    });
+  }
+}
+```
+
+```
+$ cdk diff -c vpcid=vpc-0cb9c31031d0d3e22
+Stack ExistsvpcStack
+Outputs
+[+] Output publicsubnets publicsubnets: {"Value":"subnet-06e0ea7dd302d3e8f,subnet-01fc0acfb58f3128f"}
+```
+
+```
+$ cdk context -j
+
+{
+  "vpc-provider:account=123456789012:filter.vpc-id=vpc-0cb9c31031d0d3e22:region=us-east-1": {
+    "vpcId": "vpc-0cb9c31031d0d3e22",
+    "availabilityZones": [
+      "us-east-1a",
+      "us-east-1b"
+    ],
+    "privateSubnetIds": [
+      "subnet-03ecfc033225be285",
+      "subnet-0cded5da53180ebfa"
+    ],
+    "privateSubnetNames": [
+      "Private"
+    ],
+    "privateSubnetRouteTableIds": [
+      "rtb-0e955393ced0ada04",
+      "rtb-05602e7b9f310e5b0"
+    ],
+    "publicSubnetIds": [
+      "subnet-06e0ea7dd302d3e8f",
+      "subnet-01fc0acfb58f3128f"
+    ],
+    "publicSubnetNames": [
+      "Public"
+    ],
+    "publicSubnetRouteTableIds": [
+      "rtb-00d1fdfd823c82289",
+      "rtb-04bb1969b42969bcb"
+    ]
+  }
+}
 ```
-cdk context --clear
-```