Skip to content

Section parameters

Parameters are used to configure stack and components in both stack manifest (hub.yaml) and component manifest (hub-component.yaml).

Parameters have a tree-like structure where leafs have values and nodes should have nested parameters:

parameters:
- name: cloud.kind
  value: aws                          # set to value provided by user
- name: cloud.regions                 # this parameter is only set for component `foo`
  component: foo
  value: [us-east-1, us-east-2]
- name: kubernetes                    # nested parameters for kubernetes
  parameters:
  - name: worker.size
    fromEnv: KUBERNETES_WORKER_SIZE   # Source value form environment variable
    default: m5.large                 # Use default if value not provided

Native YAML syntax could be used to short-circuit nested declarations. The above is effectively flattened into list of parameters:

cloud.kind
cloud.regions
kubernetes.worker.size

The values are in most cases plain text / scalar type, yet we support arrays and maps - data types native to JSON and YAML.

Resolve parameter value

Here we specify parameter types and their interpretation.

This is the most common type of parameter. It is used to set parameter value to a literal:

parameters:
- name: kubernetes.namespace
  value: kube-system

with interpolation 

parameters:
- name: dns.domain
  value: example.com
- name: ingress.hosts
  value: www.${dns.domain}
  # resolves to: www.example.com

or multiline parameters

parameters:
- name: ingress.hosts
  value: |
    example.com
    www.example.com

Parameter fromEnv

Stack Level only

This parameter only forks for stack manifests (hub.yaml and params-*.yaml). It allows to set parameter value from environment variable:

parameters
- name: kubernetes.namespace
  fromEnv: NAMESPACE
  default: kube-system

Parameter above will set value of parameter kubernetes.namespace to value of environment variable NAMESPACE

During hubctl stack configure user will be prompted to provide value for parameter kubernetes.namespace with default value kube-system.

Parameter env

Component Level only

This parameter only works for component manifests (hub-component.yaml). It allows to set environment variables from parameter value:

parameters:
- name: kubernetes.namespace
  env: NAMESPACE
  value: kube-system

Parameter above will define environment variable NAMESPACE with value kube-system as a default (unless stack will provide different name)

Parameter fromFile

Parameter value could be read from file fromFile: config/stage/password.

CEL expressions

Parameter value support CEL expressions enclosed in #{} such as:

parameters:
- name: cloud.availabilityZones
- name: cloud.availabilityZones.count
  value: "#{len(cloud.availabilityZones)}"

CEL has some unexpected results for corner cases, use hubctl cel to debug.

Parameter kind

All parameters can be derived from primarily from values or other components. These parameters resolved during the deployment. Until you are not care for specific parameter kind then leave it out.

However there are special case parameters. In this case you define a special attribute kind to specify how parameter should be resolved.

Parameter kind: user

There are high-level user-provided parameters - the facts user do care about: which cloud and cloud account to use, what region to deploy to, etc.

In general, preferred approach to resolve parameters provided as outputs from the component is through components.depends attribute. However sometimes you need to change parameter name as they are not match.

To map output to a different name use kind: link parameter. The interpretation of value will be deferred until parameter is used:

parameters:
- name: backend.image
  value: ${ecr:docker.image}
  kind: link

ecr is a component deployed prior to backend. There are several ECRs thus output is fully qualified.

See also

Last update: August 30, 2023