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- Now let's review
bootstrapping with Userdata.

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Within EC2 Userdata,

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are scripts that would allow

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an instance to configure itself.

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So remember that earlier
we talked about how

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with the on-demand nature of EC2,

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we can launch a machine at any time.

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And when that machine comes to life,

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we need that machine to perhaps
start certain processes,

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perhaps download different pieces of code,

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or call home to a configuration
management service.

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But so the Userdata allows us to do that.

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It is one of the keys to high-availability

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and self-healing, right?

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When we think about an
environment in which

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due to the disposable
nature of EC2 instances,

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they really can come and go at anytime,

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and so as we'll talk about later,

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when we get into Auto Scaling,

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you can imagine that if
we were to create a system

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where with very little
manual intervention,

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and we have a machine come to life,

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we need a way for this
machine to configure itself.

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And in doing so and
creating that kind of thing

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with Auto Scaling and
automatic bootstrapping,

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we can create self-healing environments.

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It's a very, very powerful pattern

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for enabling fault tolerance
and high-availability

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and efficiency in our processes.

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And so, the Userdata that we have,

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we do have a limit of 16 K.

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And these scripts are
executed on the first boot,

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at launch on the first boot.

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And so if we were to reboot that machine,

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no matter how many times,

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that script would never
be executed a second time.

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It's only executed during
the first boot, right?

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Now it doesn't have to be a script,

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it can be a list of
environment variables as well.

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So, for different operating systems,

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while in Linux we have the ability

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to create simple bash scripts,

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or it could be Node.js, or Python,

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or pretty much any executable binary

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that we can list, right?

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And in basically any other executable.

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For Windows, we can use a batch script,

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or a powershell script.

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So either way, we have this
really powerful ability

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to give our EC2 instance
enough information

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to get itself up and running,

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doing what it's supposed to do,

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without manual intervention.

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And so when we combine Userdata with

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the Instance Metadata Service,

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with custom private Amazon machine images,

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that gives us a very powerful tool

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for creating a very efficient,
automated, self-healing,

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and fault-tolerant environment.