gcloud-func-pubsub-dlt-missing: Configure Dead Lettering for Pub/Sub-Triggered Functions

id: gcloud-func-pubsub-dlt-missing

info:
  name: Configure Dead Lettering for Pub/Sub-Triggered Functions
  author: princechaddha
  severity: low
  description: |
    Ensure that Google Cloud functions triggered by Pub/Sub have a Dead-Letter Topic (DLT) configured to handle undeliverable messages. To achieve this, configure your Pub/Sub subscriptions with a maximum number of delivery attempts. If a message cannot be delivered, it will be sent to the designated Dead-Letter Topic (DLT).
  impact: |
    Not having a Dead-Letter Topic for Pub/Sub-triggered functions can result in lost messages and unhandled failures, affecting the reliability of your application.
  remediation: |
    Configure a Dead-Letter Topic for each Pub/Sub-triggered function by setting up the necessary Pub/Sub subscription settings.
  reference:
    - https://cloud.google.com/functions/docs/calling/pubsub#retry
  tags: cloud,devops,gcp,gcloud,google-cloud-functions,gcp-cloud-config

flow: |
  code(1)
  for(let projectId of iterate(template.projectIds)){
    set("projectId", projectId)
    code(2)
    for(let functionDetail of iterate(template.functions)){
      set("functionName", functionDetail)
      code(3)
    }
  }

self-contained: true

code:
  - engine:
      - sh
      - bash
    source: |
      gcloud projects list --format="json(projectId)"

    extractors:
      - type: json
        name: projectIds
        internal: true
        json:
          - '.[].projectId'

  - engine:
      - sh
      - bash
    source: |
      gcloud functions list --project $projectId --format="json(name, region)"

    extractors:
      - type: json
        name: functions
        internal: true
        json:
          - '.[].name'

  - engine:
      - sh
      - bash
    source: |
      gcloud functions describe $functionName --format="json(eventTrigger.pubsubTopic)"

    matchers:
      - type: word
        words:
          - 'null'

    extractors:
      - type: dsl
        dsl:
          - '"Missing Dead Letter Topic for function: " + functionName + " in Project: " + projectId'
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