Connection Draining enables AWS customers to shutter unneeded virtual servers without disrupting users’ in-flight requests to apps.

Amazon has a brand new service, highlighted in a tweet by AWS CTO Werner Vogels on Thursday: Elastic Load Balancing now supports Connection Draining, he said, calling it “good news.”

Amazon’s Elastic Load Balancing service enables a hectic application to spread incoming traffic over a couple of instance of the applying for better response times. When combined with Amazon’s Auto Scaling service, both act together to dynamically allocate and reallocate resources in Amazon’s Elastic Compute Cloud to fit a customer’s needs. Just as traffic often increases, it also decreases, necessitating a scaling back of resources.

That’s where Connection Draining is available in. It’s needed during a workload’s scale-back period within the cloud. When traffic diminishes from a peak, instances and network connections needs to be shut down. Closing network connections risks disrupting application responses which are still within the delivery stage. If they’re closed clumsily, users may even see page freezes or file download disruptions.

“You want to bypass breaking open network connections, while taking an instance out of service, updating its software, or replacing it with a fresh instance that contains updated software,” wrote AWS cloud evangelist Jeff Barr in a blog post on Thursday. Breaking them inadvertently means frustrated customers somewhere, he noted.

[Learn more about Cloud Services And The Hidden Cost Of Downtime.]

By applying Connection Draining to Elastic Load Balancing, Amazon customers can avoid that disruption. The buyer can designate a “timeout” period between when an instance dies and when the network connections that served it would close. By building in a lag time, user responses may finish delivering, even after the example have been eliminated. A timeout could be one second or 60 minutes, if the buyer wants a protracted safeguard period.

As the example disappears off the weight balancer’s registry, the weight balancer still knows how long it’ll allow in-flight requests to the workload to finish, and likewise knows to send no new requests to the discontinued virtual machine. Once the time-out period is exhausted, however, the network connections are closed, and no remaining in-flight requests will complete.

Connection Draining may be activated at the AWS Management Console on the customer’s datacenter. Customers has to be using the most recent version of the console. Clicking at the small blue cartoon bubble within the tool bar on the top right corner of the console enables the brand new console version to load, Barr wrote. A manager can click a load balancer, modify it by enabling the recent Connection Draining capability, and save the change. A customer may also implement it during the AWS command line interface or by calling the Modify LoadBalancerAttributes function within the load balancer API. The feature is usually added to an existing load balancer and can be added by default to new load balancers.

Connection Draining is this kind of enhancement to a cloud service that permits it to function in a fashion more a bit like on-premises applications. System administrators in an enterprise datacenter shouldn’t have to fret about physical network connections disappearing, so all in-flight requests are completed. But trying to manage a cloud workload in an identical manner has its awkward moments, one being when the example must be shut down however the manager can’t tell whether all its end-user requests have completed.

For AWS customers with fluctuating traffic performing on their web servers and applications in EC2, Connection Draining is in a different way to smooth out the variations between workloads running on premises and an identical workloads within the cloud.

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Charles Babcock is an editor-at-large for InformationWeek, having joined the publication in 2003. He’s the previous editor-in-chief of Digital News, former software editor of Computerworld and previous technology editor of Interactive Week. He’s a graduate of Syracuse … View Full Bio

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