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Probes are defined within the variables section of your .preflight.yaml. 
variables:
  VARIABLE_NAME:
    probe:
      type: probe_type
      timeout: 5000 # Optional, in ms
      target: "optional override"

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Database Probes

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PostgreSQL (postgres)

Verifies that the provided connection string is valid and that a SELECT 1 query succeeds. 
DATABASE_URL:
  probe: { type: postgres }

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MongoDB (mongodb)

Verifies that the MongoDB client can connect and perform an admin ping. Supports standard and SRV connection strings. 
MONGODB_URI:
  probe: { type: mongodb }

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Cache Probes

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Redis (redis)

Verifies that the Redis server is reachable and responds to a PING command. 
REDIS_URL:
  probe: { type: redis }

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Cloud & API Probes

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AWS (aws)

Verifies that the AWS credentials in the environment (AWS_ACCESS_KEY_ID, etc.) are valid by calling sts:GetCallerIdentity. 
AWS_REGION:
  probe: { type: aws }

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HTTP/HTTPS (http)

Verifies that a URL is reachable. By default, it checks for a 2xx response. 
STRIPE_API_ENDPOINT:
  probe:
    type: http
    target: "https://api.stripe.com/health"
    expectStatus: 200 # Optional

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Network Probes

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TCP (tcp)

A generic port-level connectivity check. Useful for internal services or protocols not yet natively supported. 
INTERNAL_SERVICE_HOST:
  probe:
    type: tcp
    target: "internal.svc.cluster.local:8080"

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Global Configuration

PropertyDescriptionDefault
typeThe type of probe to run.(Required)
timeoutMax time in milliseconds to wait for a connection.5000
targetOverride the value used for the probe (e.g., if the variable is just a password).(Value of variable)
expectStatusThe expected HTTP status code (for http probes only).2xx