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Topo: Terraform Provisioner

Topo helps with managing multiple provisions of the same Terraform scripts. Topo clones a Terraform project specified in a configuration file, and runs parameterized Terraform commands on it. Topo uses Goroutines to run Terraform commands and perform certain tasks concurrently. This helps Topo achieve acceptable speed.

Topo configuration file format:

tf_repo: <git_repo_url> # git URL where Terraform project is located.
s3_bucket: <s3_bucket> # s3 bucket where Terraform remote state resides.
provisions:
    <name>
        action: apply | destroy
        state: applied | changed | destroyed # optional
        parameters:
            <key>: <value>

Topo currently only works with AWS Terraform provider and S3 remote backend.

Usage

  1. Create a yaml file using the Topo config format (you can refer to topo-sample.yml), and name it whatever you want.

  2. Export the following environment variables:

     $ export AWS_ACCESS_KEY_ID="accesskey" # For tf to access AWS.
 $ export AWS_SECRET_ACCESS_KEY="secretkey"
 $ export AWS_DEFAULT_REGION="us-east-1"
 $ export TF_VAR_access_key=$AWS_ACCESS_KEY # Not necessary if the variable is not defined in your tf project.
 $ export TF_VAR_secret_key=$AWS_SECRET_ACCESS_KEY # Not necessary if the variable is not defined in your tf project.
 $ export TP_GIT_USER=<git_username> # Git credentials if tf project is in a private repository.
 $ export TP_GIT_PASSWORD=<git_password>

  3. Run Topo with config created in step 1:

     $ topo [flags...] topo-sample.yml

    Available flags are:

    • -update: when specified guarantees that the terraform project will be fetched from remote, even if it was previously fetched. Note that flags must appear before the name of the config file, e.g.:

        $ topo -update <config_file>

What does Topo do?

  1. Accepts and parses a YAML configuration file. A configuration file should contain one or more provision blocks, which look like:

     provisions:
   jenkins_2:
     action: apply
     state: changed
     parameters:
       desired_service_count: 1
       desired_instance_capacity: 1
       max_instance_size: 1

  2. Each provision should have an action and/or state. A state may have the value applied, destroyed, or changed. An action may be either apply or destroy. The default action is apply and there is no default state. The provision will be ignored if any one of the following cases are true:

    • changed state with a destroy action.
    • destroyed state with a destroy action.
    • applied state with an apply action.

    The cases above are referred to as the ignore criteria.

  3. Topo runs a parameterized terraform (tf) command on all provisions in the config based on their action and optional state.

  4. A topo run involves the following:

    1. Cloning a git repo that contains tf scripts.
    2. Configuring and syncing the tf remote state.
    3. Running a tf command if none of the ignore criteria is met.

  5. For each successful tf command, the provision's state in the config file is updated to either applied or destroyed. For example, this Topo config:

     tf_repo: https://github.com/shuaibiyy/ecs-jenkins.git
 s3_bucket: flexisaf-topo
 provisions:
   jenkins_1:
     action: destroy
     state: applied
     parameters:
       desired_instance_capacity: "2"
       desired_service_count: "3"
       max_instance_size: "2"
   jenkins_2:
     action: apply
     state: changed
     parameters:
       desired_instance_capacity: "1"
       desired_service_count: "1"
       max_instance_size: "1"

    is turned into (note the change in provision states):

     tf_repo: https://github.com/shuaibiyy/ecs-jenkins.git
 s3_bucket: flexisaf-topo
 provisions:
   jenkins_1:
     action: destroy
     state: destroyed
     parameters:
       desired_instance_capacity: "2"
       desired_service_count: "3"
       max_instance_size: "2"
   jenkins_2:
     action: apply
     state: applied
     parameters:
       desired_instance_capacity: "1"
       desired_service_count: "1"
       max_instance_size: "1"

What doesn't Topo do?

Topo requires you to create a configuration file and add provisions by hand. It also requires you to update the state of a provision to changed when you add, delete or modify its parameters. If you want Topo to skip a provision, you can set its state and action to match one of the ignore criteria.