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https://github.com/gposton/sagan

Blue/Green deployments in AWS using Terraform
https://github.com/gposton/sagan

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Blue/Green deployments in AWS using Terraform

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# sagan

Blue/Green deployments in AWS using Terraform



Carl Sagan originally proposed terraforming Venus to make it habitable

for human life.



This repo contains a set of scripts that can be used to trigger a

blue/green deployment in AWS using auto scaling groups and immutable

AMIs.



The process is as follows:



1. Remove the reference to the ASG and Launch config from terraform

   state file (terraform.tfstate)

1. Run terraform apply which will create a new ASG and launch

   configuration with the new AMI.

1. Verify functionality of the application.

1. Put the instances in the original ASG in 'Standby' mode so that it

   doesn't recieve new traffic.

1. Verify functionality of the application.

1. Delete the ASG (and associated instances) from AWS.



# How to



Given the terraform apply has been ran with the example template...



Set your AWS keys and install gem dependencies:



```

➜  sagan git:(master) ✗ export AWS_ACCESS_KEY_ID=

➜  sagan git:(master) ✗ export AWS_SECRET_ACCESS_KEY=

➜  sagan git:(master) ✗ sudo gem install bundler

➜  sagan git:(master) ✗ bundle

```



Remove the reference to the ASG and Launch config from terraform state

file:



```

➜  sagan git:(master) ✗ ./remove_asg_from_tfstate.rb example_template/terraform.tfstate

Creating tfstate backup at example_template/terraform.tfstate.1430149712

Removed the following asg from example_template/terraform.tfstate:

web_ami-2593a715

```



Note the asg id above... you'll need this later (to take it out of service)



Run terraform apply to create the new ASG and launch config:



```

➜  sagan git:(master) ✗ cd example_template



➜  example_template git:(master) ✗ terraform apply

var.ami

  the AMI to use



  Enter a value: ami-c1a194f1



var.availability_zones

  A comma separated list of availability zones (no spaces)



  Enter a value:



var.count

  the number of instances to run



  Default: 3

  Enter a value:



var.instance_size

  EC2 instance size



  Default: t2.micro

  Enter a value:



var.key_name

  The name of the aws key used to launch instances



  Enter a value:



var.private_subnets

  A comma separated list of subnet ids (no spaces)



  Enter a value:



var.region

  the region we are gong to run in



  Enter a value:



var.vpc_id

  A vpc id



  Enter a value:



aws_security_group.web_server: Refreshing state... (ID: sg-fcccc799)

aws_elb.web_lb: Refreshing state... (ID: web-elb)

aws_launch_configuration.launch_config: Creating...

...

aws_launch_configuration.launch_config: Creation complete

aws_autoscaling_group.asg: Creating...

...

aws_autoscaling_group.asg: Creation complete



Apply complete! Resources: 2 added, 0 changed, 0 destroyed.



The state of your infrastructure has been saved to the path

below. This state is required to modify and destroy your

infrastructure, so keep it safe. To inspect the complete state

use the `terraform show` command.



State path: terraform.tfstate

```



Verify functionality of the application and then put the original ASG

in standby:



```

➜  example_template git:(master) ✗ cd ..



➜  sagan git:(master) ✗ ./put_asg_in_standby.rb -h

Usage: put_asg_in_standby.rb -a ASG [-r REGION] [-x]

    -a, --asg ASG                    Name of the ASG to remove (required)

    -r, --region REGION              Name of the AWS region to use (default: us-west-2)

    -x, --exit-standby               If set, remove the ASG from standby

    -h, --help                       Prints this help



➜  sagan git:(master) ✗ ./put_asg_in_standby.rb -a web_ami-2593a715

Putting the following instances on standby:

i-56e078a0

i-d8fcd211

i-17be76e0

```



Verify the functionality of the application then terminate the original

ASG (You will not be able to roll back after this step):



```

➜  sagan git:(master) ✗ ./terminate_asg.rb -h

Usage: remove_asg_from_elb.rb -a ASG [-r REGION] [-x]

    -a, --asg ASG                    Name of the ASG to remove (required)

    -r, --region REGION              Name of the AWS region to use (default: us-west-2)

    -h, --help                       Prints this help



➜  sagan git:(master) ✗ ./terminate_asg.rb -a web_ami-2593a715

```



# Rollback



To remove an ASG from standby and put it back in service run:



```

➜  sagan git:(master) ✗ ./put_asg_in_standby.rb -a web_ami-c1a194f1 -x

Removing the following instances from standby:

i-ade27a5b

i-e1fad428

i-09bf77fe

```



You can now put the new ASG in standby to debug it (or delete it for

a full rollback).