pointer

Toa Pointer

The Pointer is a mechanism to deploy and resolve at runtime a set of URLs. Used by connectors and extensions.

Annotation syntax

The Pointer annotation is an object whose keys are arbitrary dot-separated strings. The meaning of these keys are defined in the corresponding module that unilizes the Poiner.

The values of the annotation object must be a URL or a list of URLs without credentials.

something:
  one: amqp://all-dummies.rmq.example.com
  two:
    - amqp://rmq0.example.com
    - amqp://rmq1.example.com

If the Pointer annotation is a string, then its value is considered as default (.).

mongodb: mongo://default.db.example.com

Shards

Pointer values can contain shards syntax.

something:
  one: redis://redis{0-2}.example.com

default namespace

When the Pointer is used for component-specific URLs and the component is in the default namespace (that is, no namepsace is specified in its manifest), the annotation value must explicitly contain the default namespace.

amqp:
  # value for the `default` namespace
  default: amqp://default-ns.rmq.example.com
  # value for `teapots` component of the `default` namespace
  default.teapots: amqp://default-dummy.rmq.example.com

Resolution

Although the most common use case of the Pointer is component-specific connection strings, where the keys are namespaces or component IDs, it is not mandatory. The Pointer considers keys as nested dot-separated alphanumeric strings.

A module that uses the Pointer, resolves a set of URLs by providing annotation and a set of selectors during deployment. The resolution finds the deepest match for a given dot-separated string within the annotation, falling back to the default URL (. key) if no matches are found.

Example

# context.toa.yaml

amqp:
  .: amqp://default.rmq.example.com # default URL
  dummies: amqp://all-dummies.rmq.example.com # default URL for the `dummies` namespace
  dummies.dummy: amqp://dummies1.rmq.example.com # URL for the `dummies.dummy` component

URL resolution for the example above is as follows:

Selector	Result	Description
dummies.dummy	amqp://d1.rmq.example.com	Exact match
dummies.another	amqp://all-dummies.rmq.example.com	Partial match
what.ever	amqp://default.rmq.example.com	No match (default)

Credentials

For security reasons, URL credentials cannot be specified in the annotation; they must be deployed secretly.

Secret names must match the annotation keys with dots replaced by dashes and prefixed by an identifier provided by the corresponding connector or extension using the Pointer.

Example

Given the AMQP binding providing amqp-context Pointer identifier and the follwing annotation:

# context.toa.yaml
amqp:
  context:
    .: amqp://default.rmq.example.com
    dummies: amqp://dummies.rmq.example.com
    dummies.dummy: amqp://dummy.rmq.example.com

Secret names for the specified keys are as follows:

• amqp-context.default
• amqp-context-dummies
• amqp-context-dummies-dummy

If secrets are not deployed with the toa conceal, then their names must be prefixed with toa-.

Only one secret can be deployed per annotation key. Therefore, when using a URL set, all URLs will utilize the same credentials.

Plain

Secret's value for plain authentication must contain username and password keys.

$ toa conceal amqp-context-dummies-dummy username=developer password=secret

TLS

Not implemented. #367

API

Deployment

import { createVariables } from '@toa.io/pointer'

// ...

const variables = createVariables(id, annotation, requests)

id is a Pointer identifier, annotation the Pointer annotation value, and requests is an array of objects conforming to the following:

# label of the component
label: string
# list of the annotation keys to be deployed for the component
selectors: string[]

Resolution

// runtime
import { resolve } from '@toa.io/pointer'

// resolve a set of URLs with credentials
// for a given pointer identifier and a selector
const urls = resolve(id, locator.id)