Pipeline stages can also be executed conditionally depending on a trigger. There is a syntax that needs to be followed for this to work as expected.

Syntax

The syntax for the expression will be of expr language. This is a simple language that can be thought of as a mix between Python and Golang.

Triggers

Triggers can be passed on a per stage basis in the following way:

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envs:
  - SOME_KEY: false

stages:
  - id: auth
    use: authorization
    trigger:
      expression: "envs.SOME_KEY == true"

In the above example the SOME_KEY value from envs is used to determine whether or not the stage should be executed.

Trigger Expression Context

The trigger expression can access a lot of things related to the pipeline including the request body, the environments values, the inputs etc. Following are the things that are passed in the root of the context for expression resolution:

  • envs: Environments of the pipeline. This includes both global_envs as well as envs. This is directly fetched from context.envs
  • context: The context passed to every stage. Can be useful to access data for a previous stage.
  • inputs: Inputs for the current stage, if any are passed.

Out of the above, the envs object contains the details about the request.

Envs

The envs field maps to an object and this object contains various fields:

  • body: Request body
  • urlValues: Query Params for the URL
  • path: Path of the URL
  • method: Method of the current request
  • origin: Origin of the request
  • ipv4: IPv4 of the request
  • ipv6: IPv6 of the request
  • category: Category of the path.
  • acl: ACL of the path, if any is provided during definition of the pipeline

Using all the above values, stages can be executed conditionally in various ways.

Things to note

ReactiveSearch Pipelines support dependencies for stages. Say there are two stages defined in the following way:

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stages:
  - id: stage 1
    use: authorization
    trigger:
      expression: "2 != 2"
  - id: stage 2
    use: elasticsearchQuery
    needs:
      - stage 1

In the above example, the stage 2 stage requires the stage 1 in order to execute. However, in the above case, the stage 1 will be marked as skipped because it's trigger will resolve to false.

When this happens, the stage 2 stage will also be marked as skipped during execution.

The following line sums up the above behavior in a sentence and should be kept in mind during writing pipelines since it can lead to weird behavior.

If one or more dependent stages of a stage is skipped due to trigger resolution, that stage will be skipped as well