Get a value from a context variable - AWS Cloud Development Kit (CDK) v2

This is the AWS CDK v2 Developer Guide. If you're using v1, see the CDK v1 Developer Guide. CDK v1 enters maintenance on June 1, 2022.

Get a value from a context variable

You can specify a context variable either as part of an AWS CDK CLI command, or in cdk.json.

To create a command line context variable, use the --context (-c) option, as shown in the following example.

cdk synth -c bucket_name=mygroovybucket

To specify the same context variable and value in the cdk.json file, use the following code.

{
  "context": {
    "bucket_name": "myotherbucket"
  }
}

To get the value of a context variable in your app, use the TryGetContext method in the context of a construct (that is, when this, or self in Python, is an instance of some construct). The example gets the context value bucket_name. If the requested value is not defined, TryGetContext returns undefined (None in Python; null in Java and C#) rather than raising an exception.

TypeScript
const bucket_name = this.node.tryGetContext('bucket_name');
JavaScript
const bucket_name = this.node.tryGetContext('bucket_name');
Python
bucket_name = self.node.try_get_context("bucket_name")
Java
String bucketName = (String)this.getNode().tryGetContext("bucket_name");
C#
var bucketName = this.Node.TryGetContext("bucket_name");

Outside the context of a construct, you can access the context variable from the app object, like this.

TypeScript
const app = new cdk.App();
const bucket_name = app.node.tryGetContext('bucket_name')
JavaScript
const app = new cdk.App();
const bucket_name = app.node.tryGetContext('bucket_name');
Python
app = cdk.App()
bucket_name = app.node.try_get_context("bucket_name")
Java
App app = App();
String bucketName = (String)app.getNode().tryGetContext("bucket_name");
C#
app = App();
var bucketName = app.Node.TryGetContext("bucket_name");

For more details on working with context variables, see Runtime context.