parameters.md

Parameters

Parameters can be defined in serverless.yml or passed via CLI with --param="<key>=<value>" flags. They can be used for example to:

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

CLI parameters

Parameters can be passed directly via CLI --param flag, following the pattern --param="<key>=<value>":

serverless deploy --param="domain=myapp.com" --param="key=value"

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

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

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.

Inheritance and overriding

Here is the priority used to resolve a ${param:XXX} variable:

• First, look in params passed with --param CLI flag
• If not found, then look in params.<stage> in serverless.yml
• If not found, then look in params.default in serverless.yml
• If not found, throw an error, or use the fallback value if one was provided: ${param:XXX, 'default value'}

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.