I have the following code that I'd like to understand:

DescribeInstanceStatusRequest instanceRequest = new DescribeInstanceStatusRequest().withInstanceIds([String of our instanceId]);
AmazonEC2 ec2 = AmazonEC2ClientBuilder.defaultClient();
ec2.startInstances([instanceID string]);
ec2.waiters().instanceStatusOK().run(new WaiterParameters<DescribeInstanceStatusRequest>().withRequest(instanceRequest));

I was assured that this will start my ec2 instance and check that it it's running. I also understand that documentation states that instanceStatusOk() will poll until my desired state is achieved. How does the 4th line know what my desired state is?

CodePudding user response：

Instance status can be one of:

ok | impaired | initializing | insufficient-data | not-applicable

The instanceStatusOK waiter method is a helper that creates a pre-configured waiter which can then be run to poll until the waiter determines whether or not the EC2 instance has the desired status (ok) or not.

It knows your desired status (of ok) because it's pre-configured with that status. You can create waiters for other status values but they don't have equivalent pre-configured helpers afaik (presumably because they're not as useful, in general).