Module: Aws::CloudWatch::Waiters

Defined in:

gems/aws-sdk-cloudwatch/lib/aws-sdk-cloudwatch/waiters.rb

Overview

Waiters are utility methods that poll for a particular state to occur on a client. Waiters can fail after a number of attempts at a polling interval defined for the service client.

For a list of operations that can be waited for and the client methods called for each operation, see the table below or the Client#wait_until field documentation for the Client.

Invoking a Waiter

To invoke a waiter, call #wait_until on a Client. The first parameter is the waiter name, which is specific to the service client and indicates which operation is being waited for. The second parameter is a hash of parameters that are passed to the client method called by the waiter, which varies according to the waiter name.

Wait Failures

To catch errors in a waiter, use WaiterFailed, as shown in the following example.

rescue rescue Aws::Waiters::Errors::WaiterFailed => error
  puts "failed waiting for instance running: #{error.message}
end

Configuring a Waiter

Each waiter has a default polling interval and a maximum number of attempts it will make before returning control to your program. To set these values, use the max_attempts and delay parameters in your #wait_until call. The following example waits for up to 25 seconds, polling every five seconds.

client.wait_until(...) do |w|
  w.max_attempts = 5
  w.delay = 5
end

To disable wait failures, set the value of either of these parameters to nil.

Extending a Waiter

To modify the behavior of waiters, you can register callbacks that are triggered before each polling attempt and before waiting.

The following example implements an exponential backoff in a waiter by doubling the amount of time to wait on every attempt.

client.wait_until(...) do |w|
  w.interval = 0 # disable normal sleep
  w.before_wait do |n, resp|
    sleep(n ** 2)
  end
end

Available Waiters

The following table lists the valid waiter names, the operations they call, and the default :delay and :max_attempts values.

waiter_name	params	:delay	:max_attempts
alarm_exists	Client#describe_alarms	5	40
composite_alarm_exists	Client#describe_alarms	5	40

Defined Under Namespace

Classes: AlarmExists, CompositeAlarmExists