Configure Log Reaction

The Log Reaction Reaction A component that receives query result changes and takes action on them. Learn more outputs query result changes Result Change Event A notification from a Continuous Query describing changes to its result set. Learn more to stdout. It’s useful for development, debugging, and simple monitoring scenarios.

Basic Configuration

reactions:
  - kind: log
    id: console-output
    queries: [my-query]
    autoStart: true

Configuration Reference

Default Output

Without custom templates, changes are logged as JSON:

[console-output] Query 'my-query' (1 items):
[console-output]   [ADD] {"id":"123","name":"Test","value":42}
[console-output]   [UPDATE] {"id":"123","name":"Test","value":42} -> {"id":"123","name":"Test","value":50}
[console-output]   [DELETE] {"id":"123","name":"Test","value":50}

Custom Templates

Use Handlebars templates for custom output formatting.

Default Template

Apply to all queries:

reactions:
  - kind: log
    id: formatted-log
    queries: [my-query]
    defaultTemplate:
      added:
        template: "[NEW] {{after.id}}: {{after.name}} = {{after.value}}"
      updated:
        template: "[UPDATE] {{after.id}}: {{before.value}} -> {{after.value}}"
      deleted:
        template: "[DELETED] {{before.id}}"

Per-Query Templates

Configure templates for specific queries:

reactions:
  - kind: log
    id: multi-query-log
    queries: [orders, inventory]
    routes:
      orders:
        added:
          template: "New order #{{after.id}} for ${{after.total}}"
        updated:
          template: "Order #{{after.id}} status: {{before.status}} -> {{after.status}}"
        deleted:
          template: "Order #{{before.id}} cancelled"
      inventory:
        added:
          template: "New product: {{after.name}} ({{after.sku}})"
        updated:
          template: "Stock update: {{after.sku}} now has {{after.quantity}} units"

Template Data

Available Variables

JSON Helper

Output entire object as JSON:

defaultTemplate:
  added:
    template: "New item: {{json after}}"

Examples

Simple Debug Logging

reactions:
  - kind: log
    id: debug
    queries: [my-query]

Formatted Alert Logging

reactions:
  - kind: log
    id: alerts
    queries: [high-priority-alerts]
    defaultTemplate:
      added:
        template: |
          ALERT: {{after.type}}
          ID: {{after.id}}
          Message: {{after.message}}
          Severity: {{after.severity}}

Multi-Query Logging

reactions:
  - kind: log
    id: audit-log
    queries: [user-changes, order-changes, inventory-changes]
    routes:
      user-changes:
        added:
          template: "[AUDIT] User created: {{after.email}}"
        updated:
          template: "[AUDIT] User updated: {{after.email}}"
        deleted:
          template: "[AUDIT] User deleted: {{before.email}}"
      order-changes:
        added:
          template: "[AUDIT] Order created: #{{after.id}} (${{after.total}})"
        updated:
          template: "[AUDIT] Order #{{after.id}} status: {{after.status}}"
      inventory-changes:
        updated:
          template: "[AUDIT] Stock change: {{after.sku}} qty={{after.quantity}}"

JSON Output for Processing

reactions:
  - kind: log
    id: json-log
    queries: [events]
    defaultTemplate:
      added:
        template: '{"event":"added","data":{{json after}}}'
      updated:
        template: '{"event":"updated","before":{{json before}},"after":{{json after}}}'
      deleted:
        template: '{"event":"deleted","data":{{json before}}}'

Example with per-query templates

This is a reaction-only excerpt (you would include it under your reactions: list):

reactions:
  - kind: log
    id: sensor-log
    queries: [all-sensors, hot-sensors]
    routes:
      all-sensors:
        added:
          template: "Sensor {{after.id}}: temp={{after.temperature}}°F, humidity={{after.humidity}}%"
        updated:
          template: "Sensor {{after.id}} update: temp={{after.temperature}}°F"
      hot-sensors:
        added:
          template: "HIGH TEMP ALERT: Sensor {{after.id}} at {{after.temperature}}°F"

Viewing Logs

Docker

docker logs -f drasi-server

Direct Execution

Logs appear in stdout when running directly:

./drasi-server --config config/server.yaml

Log Level

Set log level to see more detail:

logLevel: debug

Or via environment:

RUST_LOG=debug ./drasi-server --config config/server.yaml

Documentation resources

Next steps

• Configure HTTP Reaction
• Configure gRPC Reaction
• Configure SSE Reaction