在heat中。一个instance的创建成功信号是在这个instance状态成为active之后发出的，这时候user-data可能还没有运行。可是heat已经觉得这个resource创建成功了，開始调度下一个resource的创建。
假设我们要建立一个webserver，这个webserver须要在databaseServer运行完user-data之后才開始创建，就须要使用AWS的waitcondition通讯机制。
- 整个流程例如以下：
Create WaitHandler -> WaitHandler Done -> Create "Database" (Dependon WaitHandler) -> Database Done -> Create "WaitCondition" (Dependon Database) -> Wait for Database signal ->Database send signal to WaitHandler ->WaitCondition Done ->Create WebServer (Dependon WaitCondition)->WebServer Done
- Template样例：
WaitHandle: {Type: ‘AWS::CloudFormation::WaitConditionHandle’} WaitCondition:
Type: AWS::CloudFormation::WaitCondition
DependsOn: WikiDatabase
Properties:
Handle: {Ref: WaitHandle}
Count: ‘1’
Timeout: ‘600’Database:
Type: AWS::EC2::Instance
Properties: UserData: Fn::Base64: Fn::Join: – /opt/aws/bin/cfn-signal -e 0 -r "Wiki server setup complete" ‘
– {Ref: WaitHandle}
– ”’
‘WebServer:
Type: AWS::EC2::Instance DependsOn: WaitCondition
