100 Days of DevOps — Day 17- Creating EC2 Instance using Terraform

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Welcome to Day 17 of 100 Days of DevOps, Let continue our journey, so far I have discussed terraform fundamentals and building VPC. Let continue our Journey and build our two EC2 instances in Public Subnet using terraform

100 Days of DevOps — Day 15- Introduction to Terraform

100 Days of DevOps — Day 16- Building VPC using Terraform

In order to deploy EC2 instance we need a bunch of resources

• AMI
• Key Pair
• EBS Volumes Creation
• User data

The first step in deploying EC2 instance is choosing correct AMI and in terraform, there are various ways to do that

• We can hardcode the value of AMI
• We can use data resource(similar to what we used for Availability Zone in VPC section) to query and filter AWS and get the latest AMI based on the region, as the AMI id is different in a different region.

NOTE: Use of data resource is not ideal and each and every used case, eg: In the case of Production we might want to use a specific version of CentOS.

• The above code will help us to get the latest Centos AMI, the code is self-explanatory but one important parameter we used is owners
• owners - (Optional) Limit search to specific AMI owners. Valid items are the numeric account ID, amazon, or self.
• most_recent - (Optional) If more than one result is returned, use the most recent AMI.This is to get the latest Centos AMI as per our use case.
• For more info

AWS: aws_ami - Terraform by HashiCorp

• Other ways to find the AMI ID

Go to https://us-west-2.console.aws.amazon.com/ec2 --> Instances --> Launch Instances --> Search for centos 

• Same thing you can do using AWS CLI

aws --region us-west-2 ec2 describe-images --owners aws-marketplace --filters Name=product-code,Values=aw0evgkw8e5c1q413zgy5pjce

• If you look at the Description field

"Description": "CentOS Linux 7 x86_64 HVM EBS 1708_11.01",

and then check the Terraform code in of the filter we use “CentOS Linux 7 x86_64 HVM EBS *” and that is one of the reasons of using that

filter {
  name   = "name"
  values = ["CentOS Linux 7 x86_64 HVM EBS *"]
}

Cloud/AWS - CentOS Wiki

• As we are able to figure out the AMI part, the next step is to create and use the key pair
• Either we can hardcode the value of key pair or generate a new key via command line and then refer to this file

$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/plakhera/.ssh/id_rsa): /tmp/id_rsa
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /tmp/id_rsa.
Your public key has been saved in /tmp/id_rsa.pub.
The key fingerprint is:
XXXXXXXXXXXXX
The key's randomart image is:
+---[RSA 2048]----+
|                 |
|                 |
|                 |
|   . . .   .   . |
|. = . +.S .o. o .|
| *.= +. .oo.oo + |
|o =+=  o o+o+ * .|
|.. ++.. +..o =.+.|
|  .o+o   Eo oo+o |
+----[SHA256]-----+

* and in var.my_public_key set the location as /tmp/id_rsa.pub
* To refer to this file, we need to use the file function

• After AMI and Keys out of our way, let start building EC2 instance

Most of these parameters I already discussed in the first section, but let's quickly review it and check the new one
* count: The number of instance, we want to create
* ami: This time we are pulling ami using data resource
* instance_type: Important parameter in AWS Realm, the type of instance we want to create
* key_name: Resource we create earlier and we are just referencing it here
Below two ones are special, because both of these resource we created during the vpc section, so now what we need to do is to output it during VPC module and use there output as the input to this module. I will discuss more about it later
* tags: Tags are always helpful to assign label to your resources.

100 Days of DevOps — Day 15- Introduction to Terraform

• If you notice the above code, one thing which is interesting here is vpc_security_group_ids and subnet_id
• The interesting part, we already created these as a part of VPC code, so we just need to call in our EC2 terraform and the way to do it using outputs.tf

• After calling these values here, we just need to define as the part of main module and the syntax of doing that is

module.<module name>.<output variable>
subnet_id      = "${module.vpc_networking.public_subnets}"                         security_group = "${module.vpc_networking.security_group}"

• Final module code for EC2 instance look like this

• Let’s create two EBS volumes and attach it to two EC2 instances we created earlier

* To create EBS Volumes, I am using ebs_volume resource and to attach it use aws_volume_attachment
* We are creating two Volumes here
* AS Volume is specific to Availibility Zone, I am using aws_availibility_zone data resource
* Size of the Volume is 10GB
* Type is gp2(other available options "standard", "gp2", "io1", "sc1" or "st1" (Default: "standard"))

AWS: aws_ebs_volume - Terraform by HashiCorp

AWS: aws_volume_attachment - Terraform by HashiCorp

• Next step is to define user data resource, what this will do, during the instance building process it’s going to attach EBS Volumes we created in earlier step.

* Special parameter in this is path.module which is going to refer to exisiting module path in our case ec2_instance

• The last step is to refer user_data resource back in your terraform code

user_data = "${data.template_file.user-init.rendered}"

• After that, You need to follow the same steps we have done while creating modules for VPC

# Step1
$ git clone https://github.com/100daysofdevops/100daysofdevops.git
Cloning into '100daysofdevops'...
remote: Enumerating objects: 83, done.
remote: Counting objects: 100% (83/83), done.
remote: Compressing objects: 100% (64/64), done.
remote: Total 83 (delta 28), reused 41 (delta 12), pack-reused 0
Unpacking objects: 100% (83/83), done.
#Step2
cd 100daysofdevops/two-tier-environment/
#Step3
Run all the terraform command
* terraform init
* terraform plan
* terraform apply

GitHub Link

100daysofdevops/100daysofdevops

Looking forward from you guys to join this journey and spend a minimum an hour every day for the next 100 days on DevOps work and post your progress using any of the below medium.

• Twitter: @100daysofdevops OR @lakhera2015
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• Slack: https://devops-myworld.slack.com/messages/CF41EFG49/
• GitHub Link:https://github.com/100daysofdevops

Reference

100 Days of DevOps — Day 0