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So let's have a look at status checks.
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So status checks on your EC2 instances
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are automatic checks done by AWS for you
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that will identify hardware and software issues
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with your EC2 instances.
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So there are two types.
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The first type is a system status check,
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and this will be a monitoring of problems that will happen
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with the systems of AWS directly.
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For example, a software or a hardware issue
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on the actual physical host that will be used,
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that will be the one that your EC2 instance is placed on.
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Or for example,
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if your host has a loss of system power and so on.
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To have an overview of these issues,
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the place to look at is the personal health dashboard.
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And this will give you information around any scheduled,
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critical maintenance by AWS
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that will affect your institute instance host,
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and therefore you need to act on it.
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So a way to act on it is to stop and start your instance.
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So let's have a look.
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As we can see here, we have a host 1.
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This is hidden to us, okay,
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but this is what happens in the data center of AWS.
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And our easy two instance is launched onto this Host 1.
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Then, say that AWS has a hardware failure.
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Then this system status check
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will be going from zero to one
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and what we have to do is to stop
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and start the EC2 instance.
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So anytime you stop an EC2 instance,
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and then you start it again.
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So not a reboot, right?
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But a stop and a start.
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Then internally what's going to happen
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is that your EC2 instance will automatically be migrated
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to a different host within AWS,
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which also explains why it will get
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a new difference public IP,
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because this will be the public IP
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of the host that you're on.
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So this is a different host migration.
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So it goes from a Host 1 to Host 2.
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And because we'll just stop and start it,
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then we know that it's moved
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and the Host 2 does not have any issues.
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And so therefore we've solved our hardware failure problem.
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The second type of problem is an instance status check.
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This is to monitor software
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and network configuration of your instance.
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For example, the network configuration becomes invalid,
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there's exhausted memory, this kind of stuff.
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In which case, to just resolve this issue,
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you should just reboot the EC2 instance
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or change the instance configuration.
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So these are the two types of status checks
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on your EC2 instance,
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but there is a way for you to automate the recovery
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and look at CloudWatch metrics.
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So CloudWatch Metrics are: StatusCheckFailed_System,
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StatusCheckFailed_Instance,
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or StatusCheckFailed if you want to regroup
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these two issues in one metric.
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So option one is choose a CloudWatch Alarm
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to recover your EC2 instance.
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So there is an action called recover instance.
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And when it's being used by CloudWatch Alarm,
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it will recover the instance by using the same private IP,
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the same public IP, the same EIP,
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the same metadata and the same placement group.
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You can also send a notification
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because it's a CloudWatch Alarm, likely to SNS.
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So your EC2 instance
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will be monitored by CloudWatch Metrics,
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for example, for the status checked failed system metric.
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The CloudWatch Alarm will be triggered
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on top of your CloudWatch Metric in case it goes to one,
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and the action of your CloudWatch Alarm
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will be to recover your EC2 instance
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by placing it somewhere else.
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You can also send a notification to Amazon SNS,
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as I just said.
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The option two, which is a bit less conventional,
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is to use an auto scaling group
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with a min, max and desired of one.
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And within health check to check for the status check
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of your EC2 instance,
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what will happen is that in case there is an issue
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with your EC2 instance,
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it will be terminated by your auto-scaling group.
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And therefore, because we have a min,
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max and desired to one,
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a new EC2 instance will be launched
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within your same auto-scaling group.
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So in this case, you don't have the same EBS volumes,
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you don't have the same private IP,
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you don't have the same elastic IP,
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but at least your instance is back up and running.
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And if you automate things well,
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then you could maybe regain back its states.
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Okay, so these are two options.
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Obviously option one's going to be much preferred
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if you have emphasis on one specific EC2 instance.
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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.
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