github.com/hobbeswalsh/terraform@v0.3.7-0.20150619183303-ad17cf55a0fa/website/source/intro/getting-started/change.html.md (about)

     1  ---
     2  layout: "intro"
     3  page_title: "Change Infrastructure"
     4  sidebar_current: "gettingstarted-change"
     5  description: |-
     6    In the previous page, you created your first infrastructure with Terraform: a single EC2 instance. In this page, we're going to modify that resource, and see how Terraform handles change.
     7  ---
     8  
     9  # Change Infrastructure
    10  
    11  In the previous page, you created your first infrastructure with
    12  Terraform: a single EC2 instance. In this page, we're going to
    13  modify that resource, and see how Terraform handles change.
    14  
    15  Infrastructure is continuously evolving, and Terraform was built
    16  to help manage and enact that change. As you change Terraform
    17  configurations, Terraform builds an execution plan that only
    18  modifies what is necessary to reach your desired state.
    19  
    20  By using Terraform to change infrastructure, you can version
    21  control not only your configurations but also your state so you
    22  can see how the infrastructure evolved over time.
    23  
    24  ## Configuration
    25  
    26  Let's modify the `ami` of our instance. Edit the "aws\_instance.example"
    27  resource in your configuration and change it to the following:
    28  
    29  ```
    30  resource "aws_instance" "example" {
    31  	ami = "ami-aa7ab6c2"
    32  	instance_type = "t1.micro"
    33  }
    34  ```
    35  
    36  We've changed the AMI from being an Ubuntu 14.04 AMI to being
    37  an Ubuntu 12.04 AMI. Terraform configurations are meant to be
    38  changed like this. You can also completely remove resources
    39  and Terraform will know to destroy the old one.
    40  
    41  ## Execution Plan
    42  
    43  Let's see what Terraform will do with the change we made.
    44  
    45  ```
    46  $ terraform plan
    47  ...
    48  
    49  -/+ aws_instance.example
    50      ami:               "ami-408c7f28" => "ami-aa7ab6c2" (forces new resource)
    51      availability_zone: "us-east-1c" => "<computed>"
    52      key_name:          "" => "<computed>"
    53      private_dns:       "domU-12-31-39-12-38-AB.compute-1.internal" => "<computed>"
    54      private_ip:        "10.200.59.89" => "<computed>"
    55      public_dns:        "ec2-54-81-21-192.compute-1.amazonaws.com" => "<computed>"
    56      public_ip:         "54.81.21.192" => "<computed>"
    57      security_groups:   "" => "<computed>"
    58      subnet_id:         "" => "<computed>"
    59  ```
    60  
    61  The prefix "-/+" means that Terraform will destroy and recreate
    62  the resource, versus purely updating it in-place. While some attributes
    63  can do in-place updates (which are shown with a "~" prefix), AMI
    64  changing on EC2 instance requires a new resource. Terraform handles
    65  these details for you, and the execution plan makes it clear what
    66  Terraform will do.
    67  
    68  Additionally, the plan output shows that the AMI change is what
    69  necessitated the creation of a new resource. Using this information,
    70  you can tweak your changes to possibly avoid destroy/create updates
    71  if you didn't want to do them at this time.
    72  
    73  ## Apply
    74  
    75  From the plan, we know what will happen. Let's apply and enact
    76  the change.
    77  
    78  ```
    79  $ terraform apply
    80  aws_instance.example: Destroying...
    81  aws_instance.example: Modifying...
    82    ami: "ami-408c7f28" => "ami-aa7ab6c2"
    83  
    84  Apply complete! Resources: 0 added, 1 changed, 1 destroyed.
    85  
    86  ...
    87  ```
    88  
    89  As the plan predicted, Terraform started by destroying our old
    90  instance, then creating the new one. You can use `terraform show`
    91  again to see the new properties associated with this instance.
    92  
    93  ## Next
    94  
    95  You've now seen how easy it is to modify infrastructure with
    96  Terraform. Feel free to play around with this more before continuing.
    97  In the next section we're going to [destroy our infrastructure](/intro/getting-started/destroy.html).