Automatic merge from submit-queue
AWS: More ELB attributes via service annotations
Replaces #25015 and addresses all of @justinsb's feedback therein. This is a new PR because I was unable to reopen#25015 to amend it.
I noticed recently that there is existing (but undocumented) precedent for the AWS cloud provider to manage ELB-specifc load balancer configuration based on service annotations. In particular, one can _already_ designate an ELB as "internal" or enable PROXY protocol.
This PR extends this capability to the management of ELB attributes, which includes the following items:
* Access logs:
* Enabled / disabled
* Emit interval
* S3 bucket name
* S3 bucket prefix
* Connection draining:
* Enabled / disabled
* Timeout
* Connection:
* Idle timeout
* Cross-zone load balancing:
* Enabled / disabled
Some of these are possibly more useful than others. Use cases that immediately come to mind:
* Enabling cross-zone load balancing is potentially useful for "Ubernetes Light," or anyone otherwise attempting to spread worker nodes around multiple AZs.
* Increasing idle timeout is useful for the benefit of anyone dealing with long-running requests. An example I personally care about would be git pushes to Deis' builder component.
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