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So let's talk about a lesser-known feature
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called EC2 Hibernate.
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So we know that we can stop and terminate instances,
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and when we do so, when we stop it,
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the data on disk, on your EBS disk,
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is going to be kept intact until the next start.
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That makes sense.
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And if we terminate it, well,
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if you set up the root volume
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to be destroyed with your instance,
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it's going to be destroyed,
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but any volume that is not set up to be destroyed
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when your instance is terminated will be kept.
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And then when you start an instance,
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well, the OS, the operating system will boot
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and then the EC2 User Data that was going to be run,
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the script, and then the OS will boot up.
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And then your application starts, your caches get warmed,
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and that can take time,
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because you are booting your machine, right?
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But the idea is that with Hibernate,
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we want to achieve a new state.
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So when we hibernate an instance, whatever was in RAM,
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the in-memory state is going to be preserved.
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What does that mean?
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That means that your instance boot is going
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to be much faster,
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because the operating system is not stopped or restarted,
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the operating system is actually just frozen,
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it's hibernated.
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And under the hood, well,
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whatever was in the RAM state is going to be written
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into a file in the root EBS volume.
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So that means that the root EBS volume must be encrypted
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and that it must have enough space to contain the RAM.
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So let me show you what happens.
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So we take an EC2 instance,
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and it's running and there is data in RAM,
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and then we start a hibernation process.
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So what happens that the instance will go
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in the stopping state,
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and the RAM is going to be dumped into your EBS volume.
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Then the instance is shut down and the RAM disappears,
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because as soon as you stop an instance the RAM goes away,
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but the EBS volume still contains the dump of the RAM.
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And then when your instance is started,
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then the RAM is going to be loaded from disk
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onto the EC2 instance memory.
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And that means that it is just as is
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your EC2 instance never got stopped.
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And we'll have a look at this in the hands-on.
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So the use cases for hibernation is
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if you want to have long-running processes
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and never actually stop them,
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or if you want to save the RAM state,
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or if you just want to reboot, like boot up fast,
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and you have services that take time to initialize.
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So you actually don't want them to initialize,
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you want them to stay up and running
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even if you hibernate your instance.
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So, some good things to know about EC2 Hibernate is that
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it supports a lot of different families.
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The instance RAM size must be less than 150 gigabytes.
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Now, that can change,
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and again, you're not tested on limits at the exam,
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but I'm just putting this as an indication for you
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to get an idea of how that works.
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It doesn't work for bare metal instances.
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It works for many different operating systems,
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including Linux and Windows.
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It works for the root volume,
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so the root volume must be an EBS volume,
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it must be encrypted, okay?
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And it must be large to contain the RAM
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that you dump onto it.
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It's available for all kind of instances,
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such as on-demand, reserved, and spot instances.
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And hibernation is meant to be no more than 60 days.
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Again, this can change,
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but right now this is the actual limits.
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Okay, so that's it for this lecture, I hope you liked it,
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and I will see you in the next lecture for a hands-on.
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