cdk-remote-stack
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    cdk-remote-stack

    Get outputs and AWS SSM parameters from cross-region AWS CloudFormation stacks

    Why

    Setting up cross-regional cross-stack references requires using multiple constructs from the AWS CDK construct library and is not straightforward.

    cdk-remote-stack aims to simplify the cross-regional cross-stack references to help you easily build cross-regional multi-stack AWS CDK applications.

    This construct library provides two main constructs:

    • RemoteOutputs - cross regional stack outputs reference.
    • RemoteParameters - cross regional/account SSM parameters reference.

    RemoteOutputs

    RemoteOutputs is ideal for one stack referencing the outputs from another across different AWS regions.

    Let's say we have two cross-regional stacks in the same AWS CDK application:

    1. stackJP - stack in Japan (JP) to create a SNS topic
    2. stackUS - stack in United States (US) to get the outputs from stackJP and print out the SNS TopicName from stackJP outputs.
    import { RemoteOutputs } from 'cdk-remote-stack';
    import * as cdk from '@aws-cdk/core';
    
    const app = new cdk.App();
    
    const envJP = {
      region: 'ap-northeast-1',
      account: process.env.CDK_DEFAULT_ACCOUNT,
    };
    
    const envUS = {
      region: 'us-west-2',
      account: process.env.CDK_DEFAULT_ACCOUNT,
    };
    
    // first stack in JP
    const stackJP = new cdk.Stack(app, 'demo-stack-jp', { env: envJP })
    
    new cdk.CfnOutput(stackJP, 'TopicName', { value: 'foo' })
    
    // second stack in US
    const stackUS = new cdk.Stack(app, 'demo-stack-us', { env: envUS })
    
    // ensure the dependency
    stackUS.addDependency(stackJP)
    
    // get the stackJP stack outputs from stackUS
    const outputs = new RemoteOutputs(stackUS, 'Outputs', { stack: stackJP })
    
    const remoteOutputValue = outputs.get('TopicName')
    
    // the value should be exactly the same with the output value of `TopicName`
    new cdk.CfnOutput(stackUS, 'RemoteTopicName', { value: remoteOutputValue })

    At this moment, RemoteOutputs only supports cross-regional reference in a single AWS account.

    Always get the latest stack output

    By default, the RemoteOutputs construct will always try to get the latest output from the source stack. You may opt out by setting alwaysUpdate to false to turn this feature off.

    For example:

    const outputs = new RemoteOutputs(stackUS, 'Outputs', { 
      stack: stackJP,
      alwaysUpdate: false,
    })

    RemoteParameters

    AWS Systems Manager (AWS SSM) Parameter Store is great to store and persist parameters and allow stacks from other regons/accounts to reference. Let's dive into the two major scenarios below:

    Stacks from single account and different regions

    In this sample, we create two stacks from JP (ap-northeast-1) and US (us-west-2). The JP stack will produce and update parameters in its parameter store, while the US stack will consume the parameters across differnt regions with the RemoteParameters construct.

        const envJP = { region: 'ap-northeast-1', account: '111111111111' };
        const envUS = { region: 'us-west-2', account: '111111111111' };
    
        // first stack in JP
        const producerStackName = 'demo-stack-jp';
        const stackJP = new cdk.Stack(app, producerStackName, { env: envJP });
        const parameterPath = `/${envJP.account}/${envJP.region}/${producerStackName}`
    
        new ssm.StringParameter(stackJP, 'foo1', {
          parameterName: `${parameterPath}/foo1`,
          stringValue: 'bar1',
        });
        new ssm.StringParameter(stackJP, 'foo2', {
          parameterName: `${parameterPath}/foo2`,
          stringValue: 'bar2',
        });
        new ssm.StringParameter(stackJP, 'foo3', {
          parameterName: `${parameterPath}/foo3`,
          stringValue: 'bar3',
        });
    
        // second stack in US
        const stackUS = new cdk.Stack(app, 'demo-stack-us', { env: envUS });
    
        // ensure the dependency
        stackUS.addDependency(stackJP);
    
        // get remote parameters by path from AWS SSM parameter store
        const parameters = new RemoteParameters(stackUS, 'Parameters', {
          path: parameterPath,
          region: stackJP.region,
        })
    
        const foo1 = parameters.get(`${parameterPath}/foo1`);
        const foo2 = parameters.get(`${parameterPath}/foo2`);
        const foo3 = parameters.get(`${parameterPath}/foo3`);
    
        new cdk.CfnOutput(stackUS, 'foo1Output', { value: foo1 });
        new cdk.CfnOutput(stackUS, 'foo2Output', { value: foo2 });
        new cdk.CfnOutput(stackUS, 'foo3Output', { value: foo3 });

    Stacks from differnt accounts and different regions

    Similar to the use case above, but now we deploy stacks in separate accounts and regions. We will need to pass an AWS Identity and Access Management (AWS IAM) role to the RemoteParameters construct to get all the parameters from the remote environment.

        const envJP = { region: 'ap-northeast-1', account: '111111111111' };
        const envUS = { region: 'us-west-2', account: '222222222222' };
    
        // first stack in JP
        const producerStackName = 'demo-stack-jp';
        const stackJP = new cdk.Stack(app, producerStackName, { env: envJP });
        const parameterPath = `/${envJP.account}/${envJP.region}/${producerStackName}`
    
        new ssm.StringParameter(stackJP, 'foo1', {
          parameterName: `${parameterPath}/foo1`,
          stringValue: 'bar1',
        });
        new ssm.StringParameter(stackJP, 'foo2', {
          parameterName: `${parameterPath}/foo2`,
          stringValue: 'bar2',
        });
        new ssm.StringParameter(stackJP, 'foo3', {
          parameterName: `${parameterPath}/foo3`,
          stringValue: 'bar3',
        });
    
        // allow US account to assume this read only role to get parameters
        const cdkReadOnlyRole = new iam.Role(stackJP, 'readOnlyRole', {
          assumedBy: new iam.AccountPrincipal(envUS.account),
          roleName: PhysicalName.GENERATE_IF_NEEDED,
          managedPolicies: [ iam.ManagedPolicy.fromAwsManagedPolicyName('AmazonSSMReadOnlyAccess')],
        })
    
        // second stack in US
        const stackUS = new cdk.Stack(app, 'demo-stack-us', { env: envUS });
    
        // ensure the dependency
        stackUS.addDependency(stackJP);
    
        // get remote parameters by path from AWS SSM parameter store
        const parameters = new RemoteParameters(stackUS, 'Parameters', {
          path: parameterPath,
          region: stackJP.region,
          // assume this role for cross-account parameters
          role: iam.Role.fromRoleArn(stackUS, 'readOnlyRole', cdkReadOnlyRole.roleArn),
        })
    
        const foo1 = parameters.get(`${parameterPath}/foo1`);
        const foo2 = parameters.get(`${parameterPath}/foo2`);
        const foo3 = parameters.get(`${parameterPath}/foo3`);
    
        new cdk.CfnOutput(stackUS, 'foo1Output', { value: foo1 });
        new cdk.CfnOutput(stackUS, 'foo2Output', { value: foo2 });
        new cdk.CfnOutput(stackUS, 'foo3Output', { value: foo3 });

    Dedicated account for a centralized parameter store

    The parameters are stored in a centralized account/region and previously provisioned as a source-of-truth configuration store. All other stacks from different accounts/regions are consuming the parameters from the central configuration store.

    This scenario is pretty much like #2. The difference is that there's a dedicated account for centralized configuration store being shared with all other accounts.

    You will need create RemoteParameters for all the consuming stacks like:

    // for StackUS
    new RemoteParameters(stackUS, 'Parameters', {
      path: parameterPath,
      region: 'eu-central-1'
      // assume this role for cross-account parameters
      role: iam.Role.fromRoleArn(stackUS, 'readOnlyRole', sharedReadOnlyRoleArn),
    })
    
    // for StackJP
    new RemoteParameters(stackJP, 'Parameters', {
      path: parameterPath,
      region: 'eu-central-1'
      // assume this role for cross-account parameters
      role: iam.Role.fromRoleArn(stackJP, 'readOnlyRole', sharedReadOnlyRoleArn),
    })

    Tools for multi-account deployment

    You will need to install and bootstrap your target accounts with AWS CDK 1.108.0 or later, so you can deploy stacks from different accounts. It adds support for cross-account lookups. Alternatively, install cdk-assume-role-credential-plugin. Read this blog post to setup this plugin.

    Limitations

    1. At this moment, the RemoteParameters construct only supports the String data type from parameter store.
    2. Maximum number of parameters is 100. Will make it configurable in the future if required.

    Contributing

    See CONTRIBUTING for more information.

    License

    This code is licensed under the Apache License 2.0. See the LICENSE file.

    Install

    npm i cdk-remote-stack

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