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Build Parameters

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A template can prompt the user for additional information when creating workspaces with parameters.

Parameters in Create Workspace screen

The user can set parameters in the dashboard UI and CLI.

You'll likely want to hardcode certain template properties for workspaces, such as security group. But you can let developers specify other properties with parameters like instance size, geographical location, repository URL, etc.

This example lets a developer choose a Docker host for the workspace:

data "coder_parameter" "docker_host" {
  name        = "Region"
  description = "Which region would you like to deploy to?"
  icon        = "/emojis/1f30f.png"
  type        = "string"
  default     = "tcp://100.94.74.63:2375"

  option {
    name = "Pittsburgh, USA"
    value = "tcp://100.94.74.63:2375"
    icon = "/emojis/1f1fa-1f1f8.png"
  }

  option {
    name = "Helsinki, Finland"
    value = "tcp://100.117.102.81:2375"
    icon = "/emojis/1f1eb-1f1ee.png"
  }

  option {
    name = "Sydney, Australia"
    value = "tcp://100.127.2.1:2375"
    icon = "/emojis/1f1e6-1f1f9.png"
  }
}

From there, a template can refer to a parameter's value:

provider "docker" {
  host = data.coder_parameter.docker_host.value
}

Types

A Coder parameter can have one of these types:

string
bool
number
list(string)

To specify a default value for a parameter with the list(string) type, use a JSON array and the Terraform jsonencode function. For example:

data "coder_parameter" "security_groups" {
  name        = "Security groups"
  icon        = "/icon/aws.png"
  type        = "list(string)"
  description = "Select appropriate security groups."
  mutable     = true
  default = jsonencode([
    "Web Server Security Group",
    "Database Security Group",
    "Backend Security Group"
  ])
}

[!NOTE] Overriding a list(string) on the CLI is tricky because:

--parameter "parameter_name=parameter_value" is parsed as CSV.

parameter_value is parsed as JSON.

So, to properly specify a list(string) with the --parameter CLI argument, you will need to take care of both CSV quoting and shell quoting.

For the above example, to override the default values of the security_groups parameter, you will need to pass the following argument to coder create:

--parameter "\"security_groups=[\"\"DevOps Security Group\"\",\"\"Backend Security Group\"\"]\""

Alternatively, you can use --rich-parameter-file to work around the above issues. This allows you to specify parameters as YAML. An equivalent parameter file for the above --parameter is provided below:

security_groups: - DevOps Security Group - Backend Security Group

Options

A string parameter can provide a set of options to limit the user's choices:

data "coder_parameter" "docker_host" {
  name        = "Region"
  description = "Which region would you like to deploy to?"
  type        = "string"
  default     = "tcp://100.94.74.63:2375"

  option {
    name = "Pittsburgh, USA"
    value = "tcp://100.94.74.63:2375"
    icon = "/emojis/1f1fa-1f1f8.png"
  }

  option {
    name = "Helsinki, Finland"
    value = "tcp://100.117.102.81:2375"
    icon = "/emojis/1f1eb-1f1ee.png"
  }

  option {
    name = "Sydney, Australia"
    value = "tcp://100.127.2.1:2375"
    icon = "/emojis/1f1e6-1f1f9.png"
  }
}

Incompatibility in Parameter Options for Workspace Builds

When creating Coder templates, authors have the flexibility to modify parameter options associated with rich parameters. Such modifications can involve adding, substituting, or removing a parameter option. It's important to note that making these changes can lead to discrepancies in parameter values utilized by ongoing workspace builds.

Consequently, workspace users will be prompted to select the new value from a pop-up window or by using the command-line interface. While this additional interactive step might seem like an interruption, it serves a crucial purpose. It prevents workspace users from becoming trapped with outdated template versions, ensuring they can smoothly update their workspace without any hindrances.

Example:

Bob creates a workspace using the python-dev template. This template has a parameter image_tag, and Bob selects 1.12.
Later, the template author Alice is notified of a critical vulnerability in a package installed in the python-dev template, which affects the image tag 1.12.
Alice remediates this vulnerability, and pushes an updated template version that replaces option 1.12 with 1.13 for the image_tag parameter. She then notifies all users of that template to update their workspace immediately.
Bob saves their work, and selects the Update option in the UI. As their workspace uses the now-invalid option 1.12, for the image_tag parameter, they are prompted to select a new value for image_tag.

Required and optional parameters

A parameter is required if it doesn't have the default property. The user must provide a value to this parameter before creating a workspace:

data "coder_parameter" "account_name" {
  name        = "Account name"
  description = "Cloud account name"
  mutable     = true
}

If a parameter contains the default property, Coder will use this value if the user does not specify any:

data "coder_parameter" "base_image" {
  name        = "Base image"
  description = "Base machine image to download"
  default     = "ubuntu:latest"
}

Admins can also set the default property to an empty value so that the parameter field can remain empty:

data "coder_parameter" "dotfiles_url" {
  name        = "dotfiles URL"
  description = "Git repository with dotfiles"
  mutable     = true
  default     = ""
}

Mutability

Immutable parameters can only be set in these situations:

Creating a workspace for the first time.
Updating a workspace to a new template version. This sets the initial value for required parameters.

The idea is to prevent users from modifying fragile or persistent workspace resources like volumes, regions, and so on.

Example:

data "coder_parameter" "region" {
  name        = "Region"
  description = "Region where the workspace is hosted"
  mutable     = false
  default     = "us-east-1"
}

You can modify a parameter's mutable attribute state anytime. In case of emergency, you can temporarily allow for changing immutable parameters to fix an operational issue, but it is not advised to overuse this opportunity.

Ephemeral parameters

Ephemeral parameters are introduced to users in order to model specific behaviors in a Coder workspace, such as reverting to a previous image, restoring from a volume snapshot, or building a project without using cache. These parameters are only settable when starting, updating, or restarting a workspace and do not persist after the workspace is stopped.

Since these parameters are ephemeral in nature, subsequent builds proceed in the standard manner:

data "coder_parameter" "force_rebuild" {
  name         = "force_rebuild"
  type         = "bool"
  description  = "Rebuild the Docker image rather than use the cached one."
  mutable      = true
  default      = false
  ephemeral    = true
}

Validating parameters

Coder supports rich parameters with multiple validation modes: min, max, monotonic numbers, and regular expressions.

Number

You can limit a number parameter to min and max boundaries.

You can also specify its monotonicity as increasing or decreasing to verify the current and new values. Use the monotonic attribute for resources that can't be shrunk or grown without implications, like disk volume size.

data "coder_parameter" "instances" {
  name        = "Instances"
  type        = "number"
  description = "Number of compute instances"
  validation {
    min       = 1
    max       = 8
    monotonic = "increasing"
  }
}

It is possible to override the default error message for a number parameter, along with its associated min and/or max properties. The following message placeholders are available {min}, {max}, and {value}.

data "coder_parameter" "instances" {
  name        = "Instances"
  type        = "number"
  description = "Number of compute instances"
  validation {
    min       = 1
    max       = 4
    error     = "Sorry, we can't provision too many instances - maximum limit: {max}, wanted: {value}."
  }
}

NOTE: as of terraform-provider-coder v0.19.0, options can be specified in number parameters; this also works with validations such as monotonic.

String

You can validate a string parameter to match a regular expression. The regex property requires a corresponding error property.

data "coder_parameter" "project_id" {
  name        = "Project ID"
  description = "Alpha-numeric project ID"
  validation {
    regex = "^[a-z0-9]+$"
    error = "Unfortunately, this isn't a valid project ID"
  }
}

Create Autofill

When the template doesn't specify default values, Coder may still autofill parameters.

Coder will look for URL query parameters with form param.<name>=<value>. This feature enables platform teams to create pre-filled template creation links.
Coder will populate recently used parameter key-value pairs for the user. This feature helps reduce repetition when filling common parameters such as dotfiles_url or region.