AWS EC2 with PHP SDK - wait until instance has Public DNS Name

Question

I want to create an ec2 instance, and use the "Waiter" functionality to wait until the Instance has a Public DNS Name - is this possible?

Here is my code:

$ec2 = new Aws\Ec2\Ec2Client([credentials]);

$result = $ec2->runInstances(array(
                'DryRun' => false,
                // ImageId is required
                'ImageId' => '[removed]',
                // MinCount is required
                'MinCount' => 1,
                // MaxCount is required
                'MaxCount' => 1,
                'KeyName' => '[removed]',
                'SecurityGroupIds' => array('[removed]'),

                'InstanceType' => 'r3.4xlarge',

                'Placement' => array(
                    'AvailabilityZone' => 'us-east-1a',

                ),
                'EbsOptimized' => false,
                'Monitoring' => array(
                    // Enabled is required
                    'Enabled' => true,
                ),

            ));

$arr = $result->toArray();

$instanceId = $arr['Instances'][0]['InstanceId'];

echo 'created instance '.$instanceId."\n";

$ec2->waitUntil('InstanceRunning', ['InstanceIds' => array($instanceId)]);          

$result = $ec2->describeInstances(array(
                'InstanceIds' => array($instanceId),
            ));
$dnsName = current($result->getPath('Reservations/*/Instances/*/PublicDnsName'));

The instance is created just fine but the last line fails, because the instance does not have a public dns name because an instance is considered 'running' before it has a dns name. Is there a waiter I can use to wait until it has a dns name?

Here are the waiters: http://docs.aws.amazon.com/aws-sdk-php/v3/api/api-ec2-2015-04-15.html#waiters

I know I can sleep, or loop through until the dns name is available, just wanted to use the cool waiter function. — James Bowler
Honestly, the waiters are just an abstraction over a loop with a call to sleep(), so that would be a valid approach. A lot of the waiters in the SDK came from customer pull requests against one or more of the AWS SDKs, so please open a PR if you come up with something! — giaour

Jordan Jordan · Accepted Answer · 2015-07-22T15:12:21

There is no waiter function to get the public DNS name. 2 options I can think of:

1.) Use sleep or some sort of while loop / sleep method until you can get the PublicDnsName. This is kind of hacky and blocks your thread.

2.) A more elegant way is to make this whole thing asynchronous by using Queuing, or a PHP implementation of asynchronous.

AWS EC2 with PHP SDK - wait until instance has Public DNS Name

2 Answers