Save and retrieve context variable values

You can specify context variables with the AWS Cloud Development Kit (AWS CDK) CLI or in the cdk.json file. Then, use the TryGetContext method to retrieve values.

Specify context variables

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"
  }
}

If you specify a context variable using both the AWS CDK CLI and cdk.json file, the AWS CDK CLI value takes precedence.

Retrieve context variable values

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.)

In this example, we retrieve the value of the bucket_name context variable. If the requested value is not defined, TryGetContext returns undefined (None in Python; null in Java and C#; nil in Go) 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.