---
title: Params
---

Additionally, the params that ufo sends to the [ruby aws-sdk](https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/ECS/Client.html#run_task-instance_method) methods to create resources can be customized with a `params.yml` file.  This allows you to customize the tool using the full power of the aws-sdk.

A starter project `.ufo/params.yml` file is generated as part of the `ufo init` command. Let's take a look at an example `params.yml`:

```yaml
<%
  # replace with actual values:
  @subnets = ["subnet-111","subnet-222"]
  @security_groups = ["sg-111"]
%>
# These params are passsed to the corresponding aws-sdk ecs client methods.
# AWS Docs example: https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/ECS/Client.html#run_task-instance_method
#
# Comments left in as examples.
# Uncomment launch_type and network_configuration sections to enable fargate.
#

# ufo ship calls create_service when service doesnt exist
create_service:
  deployment_configuration:
    maximum_percent: 200
    minimum_healthy_percent: 100
  desired_count: 1
  # launch_type: "FARGATE"
  # network_configuration:
  #   awsvpc_configuration:
  #     subnets: <%= @subnets.inspect %> # required
  #     security_groups: <%= @security_groups.inspect %>
  #     assign_public_ip: "ENABLED" # accepts ENABLED, DISABLED


# ufo ship calls update_service when service already exists
# update service is provide as an example below.  Though it is probably better
# to not add any options to update_service if you are using the ECS console
# to update these settings often.
update_service:

# ufo task calls run_tasks
run_task:
  # launch_type: "FARGATE"
  # network_configuration:
  #   awsvpc_configuration:
  #     subnets: <%= @subnets.inspect %> # required
  #     security_groups: <%= @security_groups.inspect %>
  #     assign_public_ip: "ENABLED" # accepts ENABLED, DISABLED
```

Ufo provides 1st class citizen access to adjust the params sent to the aws-sdk calls:

* create_service - `ufo ship` calls this when the ECS service does not yet exist.
* update_service - `ufo ship` calls this when the ECS service already exists.
* run_task - `ufo task` calls this.

The parameters from this `params.yml` file get merged with params ufo generates internally.  Here's an example of where the merging happens in the source code for the run task command [task.rb](https://github.com/tongueroo/ufo/blob/90f12df035843528770122deb328d150249a25e2/lib/ufo/task.rb#L20).  Also, here's the starter [params.yml source code](https://github.com/tongueroo/ufo/blob/master/lib/template/.ufo/params.yml) for reference.

ERB and [shared variables]({% link _docs/variables.md %}) are available in the params file.  Notice how ERB is used at the top of the example file to set some subnets to prevent duplication. You can also define the subnets in your config/variables and use them in them in the params.yml file.

NOTE: The params.yml file does not have access to the `task_definition_name` helper method. That is only available in the `task_definitions.rb` template_definition code blocks.

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