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Links define an association between two components. Linking one component (the link source) to another (the link target) grants the source component access to the configuration of the target.

Links enable a consistent approach to sharing configuration across component types. You can view the structure for a link at the AttributeSets and Reference data page.

One of the primary purposes for links is to assign permissions between two components. Each component may expose a collection of Roles which control permissions to its resources. A Link configuration with a Role will then grant those permissions to the source component.

Provider resources that are created as a result of a link belong to the component it is defined on, regardless of Link direction.

When linking to a component, you must specify the Tier and Component attributes. Links to a SubComponent first link to the parent using the Component attribute and then use the specific attribute type named for that SubComponent. To create a link to a Lambda Function for example, the Component attribute is used to filter to the parent, whilst the Function attribute specifies the exact Function SubComponent.

Link definitions assume both source and target have matching "Instance" and "Version" identifiers. Where this is not the case the difference must be explicitly configured using attributes Instance and/or Version .

The example below shows:

  • example-function linking to example-db example-db has different Instance and Version so they are defined on the link.
  • second-example-function linking to example-db Instance and Version match, so they are not required.
  • example-db linking to example-function example-function has neither Instance or Version , but example-db has both - empty strings define the difference.

Linking to a Component

json { "Tiers" : { "db" : { "Components" : { "example-db" : { "db" : { "Instances" : { "example-instance" : { "Versions" : { "v1" : { "DeploymentUnit" : [ "example-db-v1" ] } } } }, // db configuration ... "Links" : { "lambda-function-link" : { "Tier" : "app", "Component" : "example-lambda", "Function" : "example-function", "Instance" : "", "Version" : "" } } } } } }, "app" : { "Components" : { "example-lambda" : { "lambda" : { // lambda configuration ... "Functions" : { "example-function" : { // function configuration ... "Links" : { "db-link" : { "Tier" : "db", "Component" : "example-db", "Instance" : "example-instance", "Version" : "v1" } } } } } }, "second-lambda-example" : { "lambda" : { // lambda configuration "Instances" : { "example-instance" : { "Versions" : { "v1" : { "DeploymentUnits" : [ "example-lambda-v1" ] } } } }, "Functions" : { "second-example-function" : { // function configuration "Links" : { "db-link" : { "Tier" : "db", "Component" : "example-db" } } } } } } } } } }

Specified with the Role attribute on a link, a Link Role informs the access requirements for the link source on the link target. For example a link created with a role of Consume will create the required provider resources for the link source to read and access anything stored by the link target.

Links are uni-directional and can be created as either Outbound (default) or Inbound. An Outbound link indicates that the link source interacts with the link target whilst Inbound is the inverse. If two components each require configuration from the other then each of them must specify their own link. Inbound links enable a component to nominate itself as the link target. This provides the component access to its own Role definitions.

The Context Model provides components with configuration outside of their own scope (product, account, tenant configuration). By compiling this information with the component, context is determined.

The IncludeInContext optional attribute on a link is used to restrict which links are included in the context. This permits environment space to be conserved where only a few attributes are necessary and prevents undesired overrides. When not specified, the context will contain all attributes regardless of whether they are missing or empty.

Run the following command in the hamlet container to validate your component's link configuration:

hamlet component describe-occurrence \