On Sun, Jul 8, 2012 at 8:27 PM, steve pirk [egrep] st...@pirk.com wrote:
I am pretty sure Netflix and others were trying to do it right, as they
all had graceful fail-over to a secondary AWS zone defined.
It looks to me like Amazon uses DNS round-robin to load balance the zones,
because they mention returning a list of addresses for DNS queries, and
explains the failure of the services to shunt over to other zones in their
postmortem.
There are also bugs from the Netflix side uncovered by the AWS outage:
Lessons Netflix Learned from the AWS Storm
http://techblog.netflix.com/2012/07/lessons-netflix-learned-from-aws-storm.html
For an infrastructure this large, no matter you are running your own
datacenter or using the cloud, it is certain that the code is not bug
free. And another thing is, if everything is too automated, then
failure in one component can trigger bugs in areas that no one has
ever thought of...
Rayson
==
Open Grid Scheduler - The Official Open Source Grid Engine
http://gridscheduler.sourceforge.net/
Elastic Load Balancers (ELBs) allow web traffic directed at a single IP
address to be spread across many EC2 instances. They are a tool for high
availability as traffic to a single end-point can be handled by many
redundant servers. ELBs live in individual Availability Zones and front EC2
instances in those same zones or in other Availability Zones.
ELBs can also be deployed in multiple Availability Zones. In this
configuration, each Availability Zone’s end-point will have a separate IP
address. A single Domain Name will point to all of the end-points’ IP
addresses. When a client, such as a web browser, queries DNS with a Domain
Name, it receives the IP address (“A”) records of all of the ELBs in random
order. While some clients only process a single IP address, many (such as
newer versions of web-browsers) will retry the subsequent IP addresses if
they fail to connect to the first. A large number of non-browser clients
only operate with a single IP address.
During the disruption this past Friday night, the control plane (which
encompasses calls to add a new ELB, scale an ELB, add EC2 instances to an
ELB, and remove traffic from ELBs) began performing traffic shifts to
account for the loss of load balancers in the affected Availability Zone.
As the power and systems returned, a large number of ELBs came up in a
state which triggered a bug we hadn’t seen before. The bug caused the ELB
control plane to attempt to scale these ELBs to larger ELB instance sizes.
This resulted in a sudden flood of requests which began to backlog the
control plane. At the same time, customers began launching new EC2
instances to replace capacity lost in the impacted Availability Zone,
requesting the instances be added to existing load balancers in the other
zones. These requests further increased the ELB control plane backlog.
Because the ELB control plane currently manages requests for the US East-1
Region through a shared queue, it fell increasingly behind in processing
these requests; and pretty soon, these requests started taking a very long
time to complete.
http://aws.amazon.com/message/67457/
*In reality, though, Amazon data centers have outages all the time. In
fact, Amazon tells its customers to plan for this to happen, and to be
ready to roll over to a new data center whenever there’s an outage.*
*That’s what was supposed to happen at Netflix Friday night. But it
didn’t work out that way. According to Twitter messages from Netflix
Director of Cloud Architecture Adrian Cockcroft and Instagram Engineer Rick
Branson, it looks like an Amazon Elastic Load Balancing service, designed
to spread Netflix’s processing loads across data centers, failed during the
outage. Without that ELB service working properly, the Netflix and Pintrest
services hosted by Amazon crashed.*
http://www.wired.com/wiredenterprise/2012/06/real-clouds-crush-amazon/
I am a big believer in using hardware to load balance data centers, and not
leave it up to software in the data center which might fail.
Speaking of services like RightScale, Google announced Compute Engine at
Google I/O this year. BuildFax was an early Adopter, and they gave it great
reviews...
http://www.youtube.com/watch?v=LCjSJ778tGU
It looks like Google has entered into the VPS market. 'bout time... ;-]
http://cloud.google.com/products/compute-engine.html
--steve pirk
