使用CDK为已有EventBus创建新Rule时遭遇ResourceAlreadyExistsException错误的解决求助

问题描述 #

我正尝试通过AWS CDK给一个已经存在的EventBus添加新规则，目的是将特定类型的事件转发到一个已有的SQS队列中，我的实现代码如下：

private void CreateNewRuleOnExistingEventBus(IQueue queue)
{
    var rule = new Rule(this, "MyNewRule", new RuleProps
    {
        RuleName = "MyNewRule",
        EventBus = new EventBus(this, "MyExistingEventBus", new EventBusProps
        {
            EventBusName = "MyExistingEventBus"
        }),
        Description = "New Rule on existing MyExistingEventBus",
        EventPattern = new EventPattern
        {
            Detail = new Dictionary<string, object>
            {
                { "Type", new[] {"MY_NEW_TYPE"} }
            }
        },
        Enabled = true
    });

    rule.AddTarget(new SqsQueue(queue));

    // ReSharper disable once ObjectCreationAsStatement
    new CfnOutput(this, ruleName, new CfnOutputProps
    {
        ExportName = ruleName,
        Value = rule.AttrArn
    });
}

报错信息 #

部署时遇到了以下错误：

Deployment failed: Error: Stack Deployments Failed: Error: The stack named ***** failed to deploy: UPDATE_ROLLBACK_COMPLETE: Event bus MyExistingEventBus already exists. (Service: AWSEvents; Status Code: 400; Error Code: ResourceAlreadyExistsException; Request ID: b4605949-3677-4a86-8185-6bb0c8d20fae; Proxy: null)

at deployStacks (/opt/hostedtoolcache/node/18.16.0/x64/lib/node_modules/aws-cdk/lib/index.js:330:130558)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async CdkToolkit.deploy (/opt/hostedtoolcache/node/18.16.0/x64/lib/node_modules/aws-cdk/lib/index.js:330:146782)
at async exec4 (/opt/hostedtoolcache/node/18.16.0/x64/lib/node_modules/aws-cdk/lib/index.js:385:51296)

解决方案 #

问题的根源在于你当前的代码是尝试创建一个新的EventBus资源，但这个名称的EventBus已经在你的AWS账户中存在了，所以CDK部署时会抛出资源已存在的错误。

正确的做法是直接引用已有的EventBus，而不是重新创建它，具体修改如下：

修改代码引用已有EventBus #

使用CDK提供的EventBus.FromEventBusName静态方法来获取已存在的EventBus实例，替换掉原来创建新EventBus的代码：

private void CreateNewRuleOnExistingEventBus(IQueue queue)
{
    // 引用已有的EventBus，而非创建新资源
    var existingEventBus = EventBus.FromEventBusName(this, "MyExistingEventBusRef", "MyExistingEventBus");

    var rule = new Rule(this, "MyNewRule", new RuleProps
    {
        RuleName = "MyNewRule",
        EventBus = existingEventBus, // 使用引用的已有EventBus
        Description = "New Rule on existing MyExistingEventBus",
        EventPattern = new EventPattern
        {
            Detail = new Dictionary<string, object>
            {
                { "Type", new[] {"MY_NEW_TYPE"} }
            }
        },
        Enabled = true
    });

    rule.AddTarget(new SqsQueue(queue));

    // 修正输出名称，避免变量未定义问题
    new CfnOutput(this, "MyNewRuleArn", new CfnOutputProps
    {
        ExportName = "MyNewRuleArn",
        Value = rule.AttrArn
    });
}

补充说明 #

• FromEventBusName方法会让CDK生成一个对已有AWS资源的引用，不会触发新资源的创建，完美解决资源已存在的问题。
• 同时要确保你的CDK执行角色拥有足够的权限，比如events:DescribeEventBus（用于读取已有EventBus信息）、events:PutRule（用于创建规则）以及events:PutTargets（用于绑定SQS目标）等权限，避免后续出现权限相关的报错。

备注：内容来源于stack exchange，提问作者user007