github.com/bengesoff/terraform@v0.3.1-0.20141018223233-b25a53629922/website/source/intro/getting-started/change.html.md (about)

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