In
the previous article
Clustering Web Servers Using ELB we saw and have learned AMI, target groups, their different configurations like
registering instances in the target group, etc. In this article, we are going to
learn and see the concept of Launch Templates and will cover the below topics.
- Creating Launch
Template
- Launching instance
from template
So, let’s get started.
Launch Template
Launch
template, as the name implies, contains all the configurations or settings that
are required to launch instances. It simplifies the process of auto-scaling
wherein we need a lot of instances to be added automatically in case of specific
needs.
So how we can create launch template?
Go
to Launch templates under instances -> Create launch template
And
select the key pair, security group of the card-web01/02.
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Here
as we can see that we have specified the AMI and given the instance type which
is t2.micro in this case and have also selected the same security group that we
have created for the web servers card-web01.
We
have added Tag Name as card-web00 as this is a template. Now
just click on Create template button and we can see that our launch template
has been successfully created.
NOTE: Instead of selecting
AMI for creating new instance, and then selecting instance type, key pair and
security group, we can directly go to launch template and give the no of
instances we want to create, as we have saved all the configurations inside the
launch template only.
Launching Instance from Template
By
now we have seen how we can create the template, so now it's time to launch some
instance(s) using the template. For
that, just go to actions and select the option launch Instance from template as
shown.
This
will take you to a page where you are required to put additional details like
how many instances you want to create using the launch template.
We
can also add tags for better searching.
Here we can give any number of instances in the number of instances option,
that we want to generate.
Finally
hit Launch instance from template and we can see that our new instance
card-web03 has been created successfully.
Thus,
we can see that in just few seconds we can launch the new instances. We can add
this newly created instance also in the target group as we registered our other
2 instances i.e. card-web01 and card-web02 respectively.
For
a launch template, we can create multiple launch template versions and each
version of the template can have different parameters to launch the instances.
So,
if you want to launch a new instance from the launch template then at that time,
we can select the launch template version and if we don’t specify any version
in particular then the default version is used. Also, we can set any version of
the launch template as the default version, but by default the first version of
the launch template is considered as the default version of the template.
Image
source: aws.amazon.com
The diagram above shows the different versions of launch template at a given point
of time.
- First
version; i.e. version 1, shows the type of instance, AMI Id, subnet and the
keypair used to launch an instance.
- Second
version adds security group to the details of the first version.
- Lastly the third version uses different values for some of the configuration parameters of the launch template.
Summary
In this article, we learned the concept of Launch template and their use case. We
also saw practically how we can set up launch template and can create the
instances in a matter of a few seconds.
I hope you find this article helpful. Stay tuned for
more … Cheers!!