Use Existing Templates

If you already have existing CloudFormation templates, you can use the --source option to reuse them. This allows you to take advantage of lono features with little effort. The source can be a file or an url.

Example

First, use lono new to quickly generate an empty lono project.

lono new infra
cd infra

Now that we’re are in a lono project. Let’s use lono with the --source option with an existing template. We’ll use a template that creates an EC2 instance.

$ URL=https://raw.githubusercontent.com/tongueroo/cloudformation-ec2-example/5c2f593/ec2.yml
$ lono summary demo --source $URL
=> CloudFormation Template Summary for template demo:
# Parameters Total (2)
# InstanceType=t3.micro #
KeyName= # (required)
# Resources:
  1 AWS::EC2::Instance
  1 AWS::EC2::SecurityGroup
  2 Total
$

The summary tells us that the template will create an EC2 Instance and a Security group. It also shows that there’s a required KeyName parameter. Next, let’s create the params file with lono seed

$ lono seed demo --source $URL
Creating starter config files for demo
      create  configs/demo/params/development.txt
$

Let’s take a look at the contents of the generated params file.

configs/demo/params/development.txt:

# InstanceType=t3.micro
KeyName= # (required)

Set a KeyPair that exists on your AWS account. You can use aws ec2 describe-key-pairs to list the KeyPairs on your account.

# InstanceType=t3.micro
KeyName=my-key-pair # must exist on your AWS account

After you set the KeyName in the params file, you’re ready to launch the CloudFormation stack which will create an EC2 instance.

Deploy Stack

Deploy the stack with lono cfn deploy

$ lono cfn deploy demo --source $URL
...
Creating demo stack.
Waiting for stack to complete
11:12:00PM CREATE_IN_PROGRESS AWS::CloudFormation::Stack demo User Initiated
11:12:04PM CREATE_IN_PROGRESS AWS::EC2::SecurityGroup InstanceSecurityGroup
11:12:08PM CREATE_IN_PROGRESS AWS::EC2::SecurityGroup InstanceSecurityGroup Resource creation Initiated
11:12:09PM CREATE_COMPLETE AWS::EC2::SecurityGroup InstanceSecurityGroup
11:12:11PM CREATE_IN_PROGRESS AWS::EC2::Instance EC2Instance
11:12:13PM CREATE_IN_PROGRESS AWS::EC2::Instance EC2Instance Resource creation Initiated
11:13:05PM CREATE_COMPLETE AWS::EC2::Instance EC2Instance
11:13:06PM CREATE_COMPLETE AWS::CloudFormation::Stack demo
Stack success status: CREATE_COMPLETE
Time took for stack deployment: 1m 10s.
$

Preview Stack

When deploying an updated template, lono will show previews of changes about to deploy. This provides you a lot of useful information before hitting the “big red button”. Lono provides 3 types of previews:

  1. Parameter diff preview: Shows parameters that were changed.
  2. Code diff preview: Shows a code diff of the template.
  3. Changeset preview: Uses the CloudFormation ChangeSet feature to show what resources will be changed.

All of the previews are useful in their own way. Here’s an updated template which will help demonstrate the previews.

Let’s also update InstanceType=t3.small in configs/demo/params/development.txt:

InstanceType=t3.small
KeyName=my-key-pair # must exist on your AWS account

Now change the URL to the updated template and preview the changes.

$ URL=https://raw.githubusercontent.com/tongueroo/cloudformation-ec2-example/a505e92/ec2.yml
$ lono cfn preview demo --source $URL
...
Parameter Diff Preview:
Running: colordiff /tmp/lono/params-preview/existing.json /tmp/lono/params-preview/new.json
2c2
<   "InstanceType": "t3.micro",
---
>   "InstanceType": "t3.small",
Code Diff Preview:
56a57
>       Monitoring: true
Changeset Preview:
CloudFormation preview for 'demo' stack update. Changes:
Modify AWS::EC2::Instance: Instance i-0ceca7445937eab93
$

We can see that:

  1. Parameter diff preview: The InstanceType has been changed from a t3.micro to t3.small
  2. Code diff preview: We can see Monitoring: true line has been added to the template
  3. Changeset preview: CloudFormation has detected that the instance will be modified.

Previews allow you to deploy CloudFormation changes with a higher level of confidence. You can deploy when you are ready:

lono cfn deploy demo --source $URL --sure

Note, deploying without --sure will prompt you with the preview, so you usually don’t have to remember to run lono cfn preview separately.

Configset: Automatically Configure Instances

Using existing templates with the --source option gives you access to all sorts of lono features. One interesting feature is configsets. Configsets are essentially configuration management. It allows you to configure your EC2 instances automatically. You can do all sorts of customizations. Some examples of things configsets can do: install packages, create files, run commands, ensure services are running.

Let’s add the httpd configset. Add the httpd gem to your Gemfile to make the configset available.

gem "httpd", git: "https://github.com/boltopspro/httpd"

Create a configs file with the following code to use the configset with the demo blueprint:

configs/demo/configsets/base.rb:

configset("httpd", resource: "Instance")

With that one line of configuration alone, you will install, configure, and run the httpd or apache2 web server. Deploy when you are ready.

lono cfn deploy demo --source $URL

You will see that lono adds the configset to the CloudFormation template for you.

Summary

We went through a few lono commands with an existing template. If you have existing templates that you would like to use, the --source option provides an excellent way to get started.

We have hardly scratched the surface of lono. There are many more lono features that make working with CloudFormation easier.

  • The Lono DSL - Generate templates from beautiful code.
  • Variables - Allows you to construct templates at compile-time where runtime Parameters do not suffice.
  • Layering - Allows you to build multiple environments like development and production.
  • Helpers support - Allow you to extend Lono and simplify code further.

Tip

To avoid having to specify --source repeatedly, you can import the template.

lono code import $URL --blueprint demo

Then your commands become simply:

lono cfn deploy demo

Pro tip: Use the <- and -> arrow keys to move back and forward.

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