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Pull request comments - expanded on EBS root volumes and IP addresses.

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Adam Nelson 2016-10-13 08:33:57 +11:00
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@ -722,7 +722,9 @@ EC2
- ❗Never use ssh passwords. Just don’t do it; they are too insecure, and consequences of compromise too severe. Use keys instead. [Read up on this](https://www.digitalocean.com/community/tutorials/how-to-set-up-ssh-keys--2) and fully disable ssh password access to your ssh server by making sure 'PasswordAuthentication no' is in your /etc/ssh/sshd_config file. If you’re careful about managing ssh private keys everywhere they are stored, it is a major improvement on security over password-based authentication.
- 🔸For all [newer instance types](https://aws.amazon.com/amazon-linux-ami/instance-type-matrix/), when selecting the AMI to use, be sure you select the HVM AMI, or it just won’t work.
- ❗When creating an instance and using a new ssh key pair, [make sure the ssh key permissions are correct](http://stackoverflow.com/questions/1454629/aws-ssh-access-permission-denied-publickey-issue).
- 🔸Sometimes certain EC2 instances can get scheduled for retirement by AWS due to “detected degradation of the underlying hardware,” in which case you are given a couple of weeks to migrate to a new instance. However you can typically stop and then start the instance which moves it to heathly host hardware, giving you control over timing of this event. Note however that you will lose any instance store volume data ([ephemeral drives](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/InstanceStorage.html)), but data on EBS volumes will be fine.
- 🔸Sometimes certain EC2 instances can get scheduled for retirement by AWS due to “detected degradation of the underlying hardware,” in which case you are given a couple of weeks to migrate to a new instance
- If your instance root device is an EBS volume, you can typically stop and then start the instance which moves it to heathly host hardware, giving you control over timing of this event. Note however that you will lose any instance store volume data ([ephemeral drives](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/InstanceStorage.html)) if your instance type has instance store volumes.
- The instance public IP (if it has one) will likely change unless you're using Elastic IPs. This could be a problem if other systems depend on the IP address.
- 🔸Periodically you may find that your server or load balancer is receiving traffic for (presumably) a previous EC2 server that was running at the same IP address that you are handed out now (this may not matter, or it can be fixed by migrating to another new instance).
- ❗If the EC2 API itself is a critical dependency of your infrastructure (e.g. for automated server replacement, custom scaling algorithms, etc.) and you are running at a large scale or making many EC2 API calls, make sure that you understand when they might fail (calls to it are [rate limited](http://docs.aws.amazon.com/AWSEC2/latest/APIReference/query-api-troubleshooting.html#api-request-rate) and the limits are not published and subject to change) and code and test against that possibility.
- ❗Many newer EC2 instance types are EBS-only. Make sure to factor in EBS performance and costs when planning to use them.