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@Stability(value=Experimental)

Package software.amazon.awscdk.services.synthetics.alpha

Amazon CloudWatch Synthetics Construct Library

See: Description

Package software.amazon.awscdk.services.synthetics.alpha Description

Amazon CloudWatch Synthetics Construct Library

---

cdk-constructs: Developer Preview

The APIs of higher level constructs in this module are in developer preview before they become stable. We will only make breaking changes to address unforeseen API issues. Therefore, these APIs are not subject to Semantic Versioning, and breaking changes will be announced in release notes. This means that while you may use them, you may need to update your source code when upgrading to a newer version of this package.

Amazon CloudWatch Synthetics allow you to monitor your application by generating synthetic traffic. The traffic is produced by a canary: a configurable script that runs on a schedule. You configure the canary script to follow the same routes and perform the same actions as a user, which allows you to continually verify your user experience even when you don't have any traffic on your applications.

Canary

To illustrate how to use a canary, assume your application defines the following endpoint: 

 % curl "https://api.example.com/user/books/topbook/"
 The Hitchhikers Guide to the Galaxy

The below code defines a canary that will hit the books/topbook endpoint every 5 minutes: 

 Canary canary = Canary.Builder.create(this, "MyCanary")
         .schedule(Schedule.rate(Duration.minutes(5)))
         .test(Test.custom(CustomTestOptions.builder()
                 .code(Code.fromAsset(join(__dirname, "canary")))
                 .handler("index.handler")
                 .build()))
         .runtime(Runtime.SYNTHETICS_NODEJS_PUPPETEER_3_8)
         .environmentVariables(Map.of(
                 "stage", "prod"))
         .build();

The following is an example of an index.js file which exports the handler function: 

 const synthetics = require('Synthetics');
 const log = require('SyntheticsLogger');
 
 const pageLoadBlueprint = async function () {
   // Configure the stage of the API using environment variables
   const url = `https://api.example.com/${process.env.stage}/user/books/topbook/`;
 
   const page = await synthetics.getPage();
   const response = await page.goto(url, { waitUntil: 'domcontentloaded', timeout: 30000 });
   // Wait for page to render. Increase or decrease wait time based on endpoint being monitored.
   await page.waitFor(15000);
   // This will take a screenshot that will be included in test output artifacts.
   await synthetics.takeScreenshot('loaded', 'loaded');
   const pageTitle = await page.title();
   log.info('Page title: ' + pageTitle);
   if (response.status() !== 200) {
     throw 'Failed to load page!';
   }
 };
 
 exports.handler = async () => {
   return await pageLoadBlueprint();
 };

Note: The function must be called handler.

The canary will automatically produce a CloudWatch Dashboard:

UI Screenshot

The Canary code will be executed in a lambda function created by Synthetics on your behalf. The Lambda function includes a custom runtime provided by Synthetics. The provided runtime includes a variety of handy tools such as Puppeteer (for nodejs based one) and Chromium.

To learn more about Synthetics capabilities, check out the docs.

Canary Schedule

You can specify the schedule on which a canary runs by providing a Schedule object to the schedule property.

Configure a run rate of up to 60 minutes with Schedule.rate: 

 Schedule schedule = Schedule.rate(Duration.minutes(5));

You can also specify a cron expression with Schedule.cron: 

 Schedule schedule = Schedule.cron(CronOptions.builder()
         .hour("0,8,16")
         .build());

If you want the canary to run just once upon deployment, you can use Schedule.once().

Canary DeleteLambdaResourcesOnCanaryDeletion

You can specify whether the AWS CloudFormation is to also delete the Lambda functions and layers used by this canary, when the canary is deleted.

This can be provisioned by setting the enableAutoDeleteLambdas property to true when we define the canary. 

 Stack stack = new Stack();
 
 Canary canary = Canary.Builder.create(stack, "Canary")
         .test(Test.custom(CustomTestOptions.builder()
                 .handler("index.handler")
                 .code(Code.fromInline("/* Synthetics handler code"))
                 .build()))
         .enableAutoDeleteLambdas(true)
         .runtime(Runtime.SYNTHETICS_NODEJS_PUPPETEER_3_8)
         .build();

Synthetic Canaries create additional resources under the hood beyond Lambda functions. Setting enableAutoDeleteLambdas: true will take care of cleaning up Lambda functions on deletion, but you still have to manually delete other resources like S3 buckets and CloudWatch logs.

Configuring the Canary Script

To configure the script the canary executes, use the test property. The test property accepts a Test instance that can be initialized by the Test class static methods. Currently, the only implemented method is Test.custom(), which allows you to bring your own code. In the future, other methods will be added. Test.custom() accepts code and handler properties -- both are required by Synthetics to create a lambda function on your behalf.

The synthetics.Code class exposes static methods to bundle your code artifacts:

Using the Code class static initializers: 

 // To supply the code from a S3 bucket:
 import software.amazon.awscdk.services.s3.*;
 // To supply the code inline:
 // To supply the code inline:
 Canary.Builder.create(this, "Inline Canary")
         .test(Test.custom(CustomTestOptions.builder()
                 .code(Code.fromInline("/* Synthetics handler code */"))
                 .handler("index.handler")
                 .build()))
         .runtime(Runtime.SYNTHETICS_NODEJS_PUPPETEER_3_8)
         .build();
 
 // To supply the code from your local filesystem:
 // To supply the code from your local filesystem:
 Canary.Builder.create(this, "Asset Canary")
         .test(Test.custom(CustomTestOptions.builder()
                 .code(Code.fromAsset(join(__dirname, "canary")))
                 .handler("index.handler")
                 .build()))
         .runtime(Runtime.SYNTHETICS_NODEJS_PUPPETEER_3_8)
         .build();
 Bucket bucket = new Bucket(this, "Code Bucket");
 Canary.Builder.create(this, "Bucket Canary")
         .test(Test.custom(CustomTestOptions.builder()
                 .code(Code.fromBucket(bucket, "canary.zip"))
                 .handler("index.handler")
                 .build()))
         .runtime(Runtime.SYNTHETICS_NODEJS_PUPPETEER_3_8)
         .build();

Note: Synthetics have a specified folder structure for canaries. For Node scripts supplied via code.fromAsset() or code.fromBucket(), the canary resource requires the following folder structure: 

 canary/
 ├── nodejs/
    ├── node_modules/
         ├── <filename>.js

For Python scripts supplied via code.fromAsset() or code.fromBucket(), the canary resource requires the following folder structure: 

 canary/
 ├── python/
     ├── <filename>.py

See Synthetics docs.

Running a canary on a VPC

You can specify what VPC a canary executes in. This can allow for monitoring services that may be internal to a specific VPC. To place a canary within a VPC, you can specify the vpc property with the desired VPC to place then canary in. This will automatically attach the appropriate IAM permissions to attach to the VPC. This will also create a Security Group and attach to the default subnets for the VPC unless specified via vpcSubnets and securityGroups. 

 import software.amazon.awscdk.services.ec2.*;
 
 IVpc vpc;
 
 Canary.Builder.create(this, "Vpc Canary")
         .test(Test.custom(CustomTestOptions.builder()
                 .code(Code.fromAsset(join(__dirname, "canary")))
                 .handler("index.handler")
                 .build()))
         .runtime(Runtime.SYNTHETICS_NODEJS_PUPPETEER_3_8)
         .vpc(vpc)
         .build();

Note: By default, the Synthetics runtime needs access to the S3 and CloudWatch APIs, which will fail in a private subnet without internet access enabled (e.g. an isolated subnnet).

Ensure that the Canary is placed in a VPC either with internet connectivity or with VPC Endpoints for S3 and CloudWatch enabled and configured.

See Synthetics VPC docs.

Alarms

You can configure a CloudWatch Alarm on a canary metric. Metrics are emitted by CloudWatch automatically and can be accessed by the following APIs:

Create an alarm that tracks the canary metric: 

 import software.amazon.awscdk.services.cloudwatch.*;
 
 Canary canary;
 
 Alarm.Builder.create(this, "CanaryAlarm")
         .metric(canary.metricSuccessPercent())
         .evaluationPeriods(2)
         .threshold(90)
         .comparisonOperator(ComparisonOperator.LESS_THAN_THRESHOLD)
         .build();
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