Parameters

Parameters can be defined in serverless.yml or in Serverless Dashboard. They can be used for example to:

  • adapt the configuration based on the stage
  • store secrets securely
  • share configuration values between team members

Stage parameters

Parameters can be defined for each stage in serverless.yml under the params key:

params:
  prod:
    domain: myapp.com
  dev:
    domain: preview.myapp.com

Use the default key to define parameters that apply to all stages by default:

params:
  default:
    domain: ${sls:stage}.preview.myapp.com
  prod:
    domain: myapp.com
  dev:
    domain: preview.myapp.com

Parameters can then be used via the ${param:XXX} variables:

provider:
  environment:
    APP_DOMAIN: ${param:domain}

The variable will be resolved based on the current stage.

Serverless Dashboard parameters

Serverless Dashboard lets you create and manage parameters, which is perfect for storing secrets securely or sharing configuration values across team members.

On top of that, Dashboard parameters can be stored on the service (applies to all stages) or on a specific instance (applies to a specific stage).

Dashboard parameters are treated as sensitive values, they are always encrypted at rest, and only decrypted during deployment or to view them in the dashboard.

Just like any other parameter, they can be used in serverless.yml via the ${param:XXX} variables:

provider:
  environment:
    STRIPE_SECRET_KEY: ${param:stripeSecret}

Creating Serverless Dashboard parameters

Parameters can be created in the Dashboard at the service level (applies to all stages) or instance level (stage-specific).

To manage parameters on a service, go to the apps section of the dashboard, and select settings under the ... menu.

To manage parameters on an instance, go to the app section of the dashboard, select the instance, and go to the params tab.

Retrieving parameters from the command line

Dashboard parameters can also be accessed on the CLI. You can use this at development time to look up the parameters without opening the dashboard, or in your CI/CD pipeline to use the parameters in custom scripts.

List parameters

If you are in a directory with a serverless.yml, the parameters will be listed for the org, app, and service specified in the serverless.yml file:

serverless param list [--stage <stage>]

If you are in a directory without a serverless.yml, or if you want to access parameters from another org, app, service, stage, or region, you can pass in the optional flags:

serverless param list
  [--org <org>]
  [--app <app>]
  [--service <service>]
  [--stage <stage>]
  [--region <region>]

Get a parameter

Individual parameters can also be accessed from the CLI using the param get sub-command. This command requires the --name <name> flag to identify the parameter name. Like the sls param list, you can optionally specify a different org, app, service, stage, ore region using flags.

serverless param get --name <name>
  [--org <org>]
  [--app <app>]
  [--service <service>]
  [--stage <stage>]
  [--region <region>]

Inheritance and overriding

Parameters can be defined in serverless.yml per stage, as well as in Serverless Dashboard on the service or the instance (stage). Here is the priority used to resolve a ${param:XXX} variable:

  • First, look in params.<stage> in serverless.yml
  • If not found, then look in the instance's parameters in the Dashboard
  • If not found, then look in params.default in serverless.yml
  • If not found, then look in the service's parameters in the Dashboard
  • If not found, throw an error, or use the fallback value if one was provided: ${param:XXX, 'default value'}

This gives you flexibility to mix serverless.yml parameters as well as secure Serverless Dashboard parameters.

This is especially useful in development when deploying to ephemeral stages (e.g. "feature-x"). The stage might not have any parameter, therefore it will default to the parameters set on the service. However, in other stages, like "prod", or "staging", you may override the service-level parameters with stage-level parameters to use values unique to that stage.

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