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- Let's talk about bootstrapping

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with what we call Userdata in Amazon EC2.

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Userdata is ultimately a
script that allows an EC2

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instance to automatically configure itself

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on first boot.

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So, this is one of the
keys, along with using

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multiple availability zones,
this is one of the keys

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to high availability and what we call

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self-healing infrastructures.

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I personally don't really
like being woken up

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at 2:00 in the morning
because Apache crashed

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or a server failed and I don't really want

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to have to get up in
the middle of the night

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and reinstall and reconfigure software.

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Ultimately, I want my
environment to automatically

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handle that stuff for me.

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Bootstrapping with
Userdata is one of the ways

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that we can do that.

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Now, again, this is executed
only on the first launch.

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What happens is this
script on that front boot,

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it will be ran and then it will be locked

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via a locked file so it
doesn't happen if you reboot.

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In the case of Linux,
if the very first line

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of your Userdata is
something like #!/bin/bash,

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then that will execute
that script using the bash

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binary executable.

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Otherwise, you can use
any executable software

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that you have installed that is a part

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of that Amazon machine image
when the instance boots.

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You could Node, Python,
Go, Ruby, the list goes on.

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In the case of Windows, we have the option

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of having that be a batch
or a powershell script.

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If you leave the top line blank,

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then Userdata would just be a
list of environment variables

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that a script that's already
a part of the machine image

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could then pick up and start using.

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So again, bootstrapping with user data

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is a really important key to
maintaining a highly available

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and self-healing environment,

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where our EC2 instances
can use this script

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to configure themselves on first boot.