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by djb_hackernews 3703 days ago
In general, if you are using ELBs you should have at least 2 instances per AZ or cross zone load balancing enabled. I've seen this get teams several times.

The other thing to consider when deploying to the cloud with load balancers is to use an immutable architecture. Taking hosts out of service, updating them, and putting them back in service is a bit cumbersome at best and leaves you vulnerable to service outages.
2 comments
faceplanter 3703 days ago
While I agree with having an immutable arch is preferable but in some cases it's not viable. In one of our projects we re-use the instances like in the article since we deploy multiple times an hour. In AWS you are billed for each started hour which in this case would mean that we would pay a lot extra if we created new instances for each deploy.
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djb_hackernews 3703 days ago
I do wish AWS had more granular EC2 billing, and I expect that to come soon since GCE offers it. But 2 things:

1) If you are at the scale of deploying several times an hour, the instance hour cost would probably look like a rounding error for your entire AWS spend, I'd imagine.

2) At that cadence you'll definitely benefit from using containers and a container scheduler (Kube, ECS, etc). Reuse the infrastructure but redeploy your apps to your hearts content.

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MBCook 3703 days ago
Is Elastic Beanstalk not an option? It doesn't replace hosts on redeploy so you wouldn't end up cycling through unnecessary instance.
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martin_ 3702 days ago
Genuine question: Why is it okay to reuse instances because it's controlled via an abstraction layer, as opposed to doing it yourself?
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MBCook 3702 days ago
I agree, that doesn't make a difference.

I only mentioned EB because it does that kind of thing for you and if you don't have a highly complicated setup it makes rolling updates without changing instances very easy.

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itaifrenkel 3703 days ago
I've heard that cross zone load balancing means the vpc encryption does not cover traffic between zones (the traffic is isolated like in ec2 classic). Is that substantiated?
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otterley 3703 days ago
Network communication between instances in a VPC is not encrypted, and never has been, to my knowledge. Perhaps you're thinking of VPN?
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